请各路大神帮忙看看哪里有问题

Question

源代码运行不报错，但是不会显示最终结果！一直是下面那个界面package com.example.a37061.myapplication;import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.ListView;
import android.widget.Switch;import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import java.util.UUID;public class MainActivity extends AppCompatActivity {
    private Switch mBluetooh;
    private ListView listView;
    private Button aBluetooh;
    private Button search;
    private List<String> data;
    // 用来保存搜索到的设备信息
    private List<String> bluetoothDevices = new ArrayList<String>();
    // ListView的字符串数组适配器
    private ArrayAdapter<String> arrayAdapter;
    private BroadcastReceiver mReceiver;    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取蓝牙适配器
        final BluetoothAdapter adpter = BluetoothAdapter.getDefaultAdapter();
        if (adpter == null) {
            //不支持蓝牙
            Log.i("bluetooh", "该手机不支持蓝牙");
            return;
        }
        //获取界面组件
        mBluetooh = findViewById(R.id.switch1);        //为开关绑定监听器
        final BluetoothAdapter finalAdpter = adpter;
        mBluetooh.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
                if (compoundButton.isChecked()) {
                    // 开启switch
                    finalAdpter.enable();
                } else {
                    //关闭switch
                    finalAdpter.disable();
                }
            }
        });        //获取界面组件
        aBluetooh = findViewById(R.id.button2);
        //为开关绑定监视器
        final BluetoothAdapter finalAdpter1 = adpter;
        aBluetooh.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //使本机蓝牙处于可见状态
                Intent enabler = new Intent(finalAdpter1.ACTION_REQUEST_DISCOVERABLE);
                //设置可见时间最多300秒
                enabler.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
                startActivity(enabler);
            }
        });        //获取界面组件
        search = findViewById(R.id.button);
        listView = (ListView) findViewById(R.id.listView);
        IntentFilter filter=new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(mReceiver,filter);
        IntentFilter filter2=new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
        registerReceiver(mReceiver,filter2);        search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                setTitle("正在扫描...");
                // 点击搜索周边设备，如果正在搜索，则暂停搜索
                if (adpter.isDiscovering()) {
                    adpter.cancelDiscovery();
                }
                adpter.startDiscovery();
            }
            public void onDestroy() {
                //解除注册
                unregisterReceiver(mReceiver);
                Log.e("destory","解除注册");
            }
            // 注册广播接收者
            private BroadcastReceiver receiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context arg0, Intent intent) {
                    // 获取到广播的action
                    String action = intent.getAction();
                    // 判断广播是搜索到设备还是搜索完成
                    if (action.equals(BluetoothDevice.ACTION_FOUND)) {
                        // 找到设备后获取其设备
                        BluetoothDevice device = intent
                                .getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                        // 判断这个设备是否是之前已经绑定过了，如果是则不需要添加，在程序初始化的时候已经添加了
                        if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                            // 设备没有绑定过，则将其保持到arrayList集合中
                            bluetoothDevices.add(device.getName() + ":"
                                    + device.getAddress() + "\n");
                            // 更新字符串数组适配器，将内容显示在listView中
                            arrayAdapter.notifyDataSetChanged();
                        }
                    } else if (action.equals(BluetoothAdapter.ACTION_DISCOVERY_FINISHED)) {
                        setTitle("搜索完成");
                    }
                }
            };
        });
    }
}<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">    <Button
        android:id="@+id/button"
        android:layout_width="334dp"
        android:layout_height="44dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="48dp"
        android:text="搜索蓝牙"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/switch1" />    <Switch
        android:id="@+id/switch1"
        android:layout_width="333dp"
        android:layout_height="34dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:text="蓝牙"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />    <Button
        android:id="@+id/button2"
        android:layout_width="334dp"
        android:layout_height="43dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="允许搜索"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/switch1" />    <TextView
        android:id="@+id/textView"
        android:layout_width="335dp"
        android:layout_height="25dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="可连接设备"
        android:textSize="18sp"
        app:layout_constraintBottom_toTopOf="@+id/listView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.515"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button"
        app:layout_constraintVertical_bias="0.009" />    <ListView
        android:id="@+id/listView"
        android:layout_width="334dp"
        android:layout_height="315dp"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" /></android.support.constraint.ConstraintLayout>

Answer 1

问题一：我没看到你的arrayAdapter在哪儿初始化的
问题二：初始化arrayAdapter后需要设置给listView
listView.setAdapter(arrayAdapter);

Answer 2

加行代码，获取到设备信息的时候给adapter添加数据                        if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                            // 设备没有绑定过，则将其保持到arrayList集合中
                            bluetoothDevices.add(device.getName() + ":"
                                    + device.getAddress() + "\n");
                            arrayAdapter.add(device.getName() + ":"
                                    + device.getAddress());
                            // 更新字符串数组适配器，将内容显示在listView中
                            arrayAdapter.notifyDataSetChanged();
                        }

Answer 3

另外我还发现你的mReceiver这个广播也没初始化
要不你先参考https://blog.csdn.net/qq_34536167/article/details/79432223这个看看

Answer 4

1楼，我加了还是不行啊@Jing丶无双 
        search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                setTitle("正在扫描...");
                adpter.startDiscovery();
                // 注册广播接收者
                BroadcastReceiver receiver = new BroadcastReceiver() {
                    @Override
                    public void onReceive(Context arg0, Intent intent) {
                        // 获取到广播的action
                        String action = intent.getAction();
                        // 判断广播是搜索到设备还是搜索完成
                        if (action.equals(BluetoothDevice.ACTION_FOUND)) {
                            // 找到设备后获取其设备
                            BluetoothDevice device = intent
                                    .getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                            setTitle("+1");
                            // 判断这个设备是否是之前已经绑定过了，如果是则不需要添加，在程序初始化的时候已经添加了
                            if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                                // 设备没有绑定过，则将其保持到arrayList集合中
                                setTitle("+2");
                                ArrayAdapter<String> qdapter=new ArrayAdapter<String>(MainActivity.this, simple_expandable_list_item_1,getData());
                                listView.setAdapter(qdapter);
                                // 更新字符串数组适配器，将内容显示在listView中
                                setContentView(listView);
                            }
                        } else if (action.equals(BluetoothAdapter.ACTION_DISCOVERY_FINISHED)) {
                            setTitle("搜索完成");
                        }
                    }
                };
            }
            public void onDestroy() {
                //解除注册
                unregisterReceiver(mReceiver);
                Log.e("destory","解除注册");
            }
        });
    }    public List<String> getData() {
        List<String> data = new ArrayList<String>();
        Intent intent = null;
        BluetoothDevice device = intent
                .getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
        bluetoothDevices.add(device.getName() + ":"
                + device.getAddress() + "\n");
        data.add(device.getName() + ":"
                + device.getAddress());
        return data;
    }
}

Answer 5

4楼也是我回答的啊，我发现你代码问题挺多的，给你提供了这个参考链接https://blog.csdn.net/qq_34536167/article/details/79432223

Answer 6

我参考了一下，但是设置了列表适配器以后，程序在手机上运行会闪退，是为什么？@Jing丶无双 

Answer 7

这是手机调试时报的错误
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.a37061.myapplication, PID: 21030
                  java.lang.RuntimeException: Error receiving broadcast Intent { act=android.bluetooth.device.action.FOUND flg=0x10 (has extras) } in com.example.a37061.myapplication.MainActivity$4@6cfee8
                      at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:965)
                      at android.os.Handler.handleCallback(Handler.java:815)
                      at android.os.Handler.dispatchMessage(Handler.java:104)
                      at android.os.Looper.loop(Looper.java:194)
                      at android.app.ActivityThread.main(ActivityThread.java:5898)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814)
                   Caused by: java.lang.ClassCastException: com.example.a37061.myapplication.MyAdapter cannot be cast to android.widget.ListAdapter
                      at com.example.a37061.myapplication.MainActivity$4.onReceive(MainActivity.java:136)
                      at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:953)
                      at android.os.Handler.handleCallback(Handler.java:815) 
                      at android.os.Handler.dispatchMessage(Handler.java:104) 
                      at android.os.Looper.loop(Looper.java:194) 
                      at android.app.ActivityThread.main(ActivityThread.java:5898) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:372) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814) 

Answer 8

Caused by: java.lang.ClassCastException: com.example.a37061.myapplication.MyAdapter cannot be 
cast to android.widget.ListAdapter
at com.example.a37061.myapplication.MainActivity$4.onReceive(MainActivity.java:136)错误是在你的MainActivity的第136行，MyAdapter不能强转换为ListAdapter，看看你自己怎么赋值的

Answer 9

而且搜不到HC-06这个设备！@Jing丶无双

Answer 10

package com.example.a37061.myapplication;import android.bluetooth.BluetoothDevice;
import android.content.Context;
import android.database.DataSetObserver;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListAdapter;
import android.widget.TextView;import java.util.List;public class MyAdapter implements ListAdapter {    private List<BluetoothDevice> mBluelist;
    private LayoutInflater layoutInflater;    public MyAdapter(MainActivity context, List<BluetoothDevice> list) {
        this.mBluelist = list;
        this.layoutInflater = LayoutInflater.from(context);
    }    @Override
    public boolean areAllItemsEnabled() {
        return false;
    }    @Override
    public boolean isEnabled(int position) {
        return false;
    }    @Override
    public void registerDataSetObserver(DataSetObserver observer) {    }    @Override
    public void unregisterDataSetObserver(DataSetObserver observer) {    }    @Override
    public int getCount() {
        return mBluelist.size();
    }    @Override
    public Object getItem(int position) {
        return mBluelist.get(position);
    }    @Override
    public long getItemId(int position) {
        return position;
    }    @Override
    public boolean hasStableIds() {
        return false;
    }    @Override
    public View getView(int position, View view, ViewGroup viewGroup) {
        ViewHolder viewHolder;
        if (view == null) {
            viewHolder = new ViewHolder();
            view = layoutInflater.inflate(R.layout.list_device_item, null);
            viewHolder.deviceName = view.findViewById(R.id.device_name);
            viewHolder.deviceAddress = view.findViewById(R.id.device_address);
            viewHolder.deviceType = view.findViewById(R.id.device_type);
            viewHolder.deviceState = view.findViewById(R.id.device_state);
            view.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) view.getTag();
        }
        //详细参考：http://blog.csdn.net/mirkowu/article/details/53862842
        BluetoothDevice blueDevice = mBluelist.get(position);
        //设备名称
        String deviceName = blueDevice.getName();
        viewHolder.deviceName.setText(TextUtils.isEmpty(deviceName) ? "未知设备" : deviceName);
        //设备的蓝牙地（地址为17位，都为大写字母-该项貌似不可能为空）
        String deviceAddress = blueDevice.getAddress();
        viewHolder.deviceAddress.setText(deviceAddress);
        //设备的蓝牙设备类型（DEVICE_TYPE_CLASSIC 传统蓝牙 常量值：1, DEVICE_TYPE_LE  低功耗蓝牙 常量值：2
        //DEVICE_TYPE_DUAL 双模蓝牙 常量值：3. DEVICE_TYPE_UNKNOWN：未知 常量值：0）
        int deviceType = blueDevice.getType();
        if (deviceType == 0) {
            viewHolder.deviceType.setText("未知类型");
        } else if (deviceType == 1) {
            viewHolder.deviceType.setText("传统蓝牙");
        } else if (deviceType == 2) {
            viewHolder.deviceType.setText("低功耗蓝牙");
        } else if (deviceType == 3) {
            viewHolder.deviceType.setText("双模蓝牙");
        }
        //设备的状态（BOND_BONDED：已绑定 常量值：12, BOND_BONDING：绑定中 常量值：11, BOND_NONE：未匹配 常量值：10）
        int deviceState = blueDevice.getBondState();
        if (deviceState == 10) {
            viewHolder.deviceState.setText("未匹配");
        } else if (deviceState == 11) {
            viewHolder.deviceState.setText("绑定中");
        } else if (deviceState == 12) {
            viewHolder.deviceState.setText("已绑定");
        }
        //返回远程设备支持的UUID。此方法从远程设备检索UUID不启动服务。 而是返回服务UUID的本地缓存。
        //如果需要刷新UUID，使用fetchUuidsWithSdp（）方法
        //ParcelUuid[] deviceUuid = blueDevice.getUuids();
        //blueDevice.fetchUuidsWithSdp(); boolean类型
        return view;
    }    private class ViewHolder {
        TextView deviceName;
        TextView deviceAddress;
        TextView deviceType;
        TextView deviceState;
    }    @Override
    public int getItemViewType(int position) {
        return 0;
    }    @Override
    public int getViewTypeCount() {
        return 0;
    }    @Override
    public boolean isEmpty() {
        return false;
    }
}手机调试时提示java.lang.IllegalArgumentException: Can't have a viewTypeCount 
但是我如果删掉它就提示未覆盖

Answer 11

那你先完全用这个链接https://blog.csdn.net/qq_34536167/article/details/79432223里面的代码看能不能搜索到你的蓝牙设备呢，如果可以的话，你再在上面进行修改，改成你想实现的效果

Answer 12

已经解决了 viewTypeCount ，把返回值改成0就没问题了，我现在要做点击链接的内容，我找了一些别人写的有点看不懂，你有什么可以推荐博客吗，注释清楚一点最好，我现在按照到的好像做不出来。@Jing丶无双 

Answer 13

已经解决了 viewTypeCount ，把返回值改成1就没问题了，我现在要做点击链接的内容，我找了一些别人写的有点看不懂，你有什么可以推荐博客吗，注释清楚一点最好，我现在按照到的好像做不出来。@Jing丶无双 

Answer 14

https://blog.csdn.net/a1533588867/article/details/52442349
这个博客分了三篇写，还是相对清晰，你先看看，试着做做

Answer 15

我现在的程序是：
package com.example.a37061.myapplication;import android.annotation.SuppressLint;
import android.app.ProgressDialog;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.ListView;
import android.widget.Switch;
import android.widget.TextView;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
public class MainActivity extends AppCompatActivity {
    private Switch mBluetooh = findViewById(R.id.switch1);
    private Button aBluetooh = findViewById(R.id.button2);
    private Button search = findViewById(R.id.button);
    private TextView humidity = findViewById(R.id.textView5);
    private Button button = findViewById(R.id.button3);
    private ListView listView = findViewById(R.id.listView);;
    private TextView textView1 = findViewById(R.id.textView1);;    private BluetoothAdapter adpter = BluetoothAdapter.getDefaultAdapter();
    private static final String TAG = "MainActivity";
    private List<BluetoothDevice> mBlueList = new ArrayList<>();
    private final static int SEARCH_CODE = 0x123;
    private static final UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取蓝牙适配器
        if (adpter == null) {
            //不支持蓝牙
            Log.i("bluetooh", "该手机不支持蓝牙");
            setTitle("该手机不支持蓝牙");
            return;
        }        //为开关绑定监听器
        final BluetoothAdapter finalAdpter = adpter;
        mBluetooh.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
                if (compoundButton.isChecked()) {
                    // 开启switch
                    finalAdpter.enable();
                    setTitle("蓝牙已经打开");
                } else {
                    //关闭switch
                    finalAdpter.disable();
                    setTitle("蓝牙已经关闭");
                }
            }
        });        //为开关绑定监视器
        aBluetooh.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //使本机蓝牙处于可见状态
                Intent enabler = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
                //设置可见时间最多300秒
                enabler.putExtra(BluetoothAdapter.EXTRA_DISCOVERABLE_DURATION, 300);
                startActivity(enabler);
            }
        });        search.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startDiscovery();
            }
        });
    }    private void startDiscovery() {
        // 找到设备的广播
        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        // 注册广播
        registerReceiver(receiver, filter);
        // 搜索完成的广播
        IntentFilter filter1 = new IntentFilter(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);
        // 注册广播
        registerReceiver(receiver, filter1);
        Log.e(TAG, "startDiscovery: 注册广播");
        startScanBluth();
    }    private final BroadcastReceiver receiver = new BroadcastReceiver() {
        @SuppressLint("SetTextI18n")
        @Override
        public void onReceive(Context context, Intent intent) {
            // 收到的广播类型
            String action = intent.getAction();
            // 发现设备的广播
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                // 从intent中获取设备
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                // 没否配对
                if (device.getBondState() != BluetoothDevice.BOND_BONDED) {
                    if (!mBlueList.contains(device)) {
                        mBlueList.add(device);
                    }
                    textView1.setText("附近设备：" + mBlueList.size() + "个\u3000\u3000本机蓝牙地址：" + getBluetoothAddress());
                    MyAdapter adapter = new MyAdapter(MainActivity.this, mBlueList);
                    listView.setAdapter(adapter);                    Log.e(TAG, "onReceive: " + mBlueList.size());
                    Log.e(TAG, "onReceive: " + (device.getName() + ":" + device.getAddress() + " ：" + "m" + "\n"));
                }
                // 搜索完成
            } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
                // 关闭进度条
                progressDialog.dismiss();
                Log.e(TAG, "onReceive: 搜索完成");
            }
            listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    if (adpter.isDiscovering()) {
                        adpter.cancelDiscovery();
                    }
                    MyAdapter adapter = new MyAdapter(MainActivity.this, mBlueList);
                    BluetoothDevice device = (BluetoothDevice) adapter.getItem(position);
                    connectDevice(device);
                }
            });
        }
    };    private void connectDevice(BluetoothDevice device) {
        try {
            //创建Socket
            BluetoothSocket socket = device.createRfcommSocketToServiceRecord(uuid);
            //启动连接线程
            socket.connect();
            InputStream inputStream = socket.getInputStream();
            final OutputStream outputStream = socket.getOutputStream();
            byte[] buffer = new byte[256];
            int bytes;
            while (true) {
                //读取数据
                bytes = inputStream.read(buffer);
                if (bytes > 0) {
                    final byte[] data = new byte[bytes];
                    System.arraycopy(buffer, 0, data, 0, bytes);
                    humidity.post(new Runnable() {
                        @Override
                        public void run() {
                            humidity.setText(new String(data));
                        }
                    });
                }
                button.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        int bytes = 1;
                        try {
                            outputStream.write(bytes);
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                });
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }    private ProgressDialog progressDialog;    private void startScanBluth() {
        // 判断是否在搜索,如果在搜索，就取消搜索
        if (adpter.isDiscovering()) {
            adpter.cancelDiscovery();
        }
        // 开始搜索
        adpter.startDiscovery();
        if (progressDialog == null) {
            progressDialog = new ProgressDialog(this);
        }
        progressDialog.setMessage("正在搜索，请稍后！");
        progressDialog.show();
    }    @Override
    protected void onDestroy() {
        super.onDestroy();
        //取消注册,防止内存泄露（onDestroy被回调代不代表Activity被回收？：具体回收看系统，由GC回收，同时广播会注册到系统
        //管理的ams中，即使activity被回收，reciver也不会被回收，所以一定要取消注册），
        unregisterReceiver(receiver);
    }    private String getBluetoothAddress() {
        try {
            BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
            Field field = bluetoothAdapter.getClass().getDeclaredField("mService");
            // 参数值为true，禁用访问控制检查
            field.setAccessible(true);
            Object bluetoothManagerService = field.get(bluetoothAdapter);
            if (bluetoothManagerService == null) {
                return null;
            }
            Method method = bluetoothManagerService.getClass().getMethod("getAddress");
            Object address = method.invoke(bluetoothManagerService);
            if (address != null && address instanceof String) {
                return (String) address;
            } else {
                return null;
            }
            //抛一个总异常省的一堆代码...
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode==SEARCH_CODE){
            startDiscovery();
        }
        Log.e(TAG, "onActivityResult: "+requestCode );
        Log.e(TAG, "onActivityResult: "+resultCode );
        Log.e(TAG, "onActivityResult: "+requestCode );
    }
}

Answer 16

他会报下面的错误，是怎么回事？@Jing丶无双 
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.a37061.myapplication, PID: 32502
                  java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.a37061.myapplication/com.example.a37061.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2596)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2754)
                      at android.app.ActivityThread.access$900(ActivityThread.java:187)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1584)
                      at android.os.Handler.dispatchMessage(Handler.java:111)
                      at android.os.Looper.loop(Looper.java:194)
                      at android.app.ActivityThread.main(ActivityThread.java:5898)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                      at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
                      at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
                      at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:56)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:202)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
                      at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                      at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                      at com.example.a37061.myapplication.MainActivity.<init>(MainActivity.java:35)
                      at java.lang.reflect.Constructor.newInstance(Native Method)
                      at java.lang.Class.newInstance(Class.java:1650)
                      at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2586)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2754) 
                      at android.app.ActivityThread.access$900(ActivityThread.java:187) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1584) 
                      at android.os.Handler.dispatchMessage(Handler.java:111) 
                      at android.os.Looper.loop(Looper.java:194) 
                      at android.app.ActivityThread.main(ActivityThread.java:5898) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:372) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814)

Answer 17

首先你得自己学会看报错，一般报错主要看两个位置：
1.报错最顶部的信息：
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.a37061.myapplication/com.example.a37061.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
这里的报错是说RuntimeException运行错误在com.example.a37061.myapplication包里的MainActivity中产生了NullPointerException空指针异常2.报错包含Caused by以下的信息：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
                      at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:117)
                      at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:149)
                      at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:56)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:202)
                      at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:183)
                      at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
                      at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
                      at com.example.a37061.myapplication.MainActivity.<init>(MainActivity.java:35)
Caused by以下的信息这最后一句就提示的很明显了MainActivity.java:35MainActivity第35行报错综上所述：
看看你的代码35行到41行
private Switch mBluetooh = findViewById(R.id.switch1);
    private Button aBluetooh = findViewById(R.id.button2);
    private Button search = findViewById(R.id.button);
    private TextView humidity = findViewById(R.id.textView5);
    private Button button = findViewById(R.id.button3);
    private ListView listView = findViewById(R.id.listView);;
    private TextView textView1 = findViewById(R.id.textView1);布局都没有加载，你就开始findViewById能不报空指针异常么，我们都是从布局里面找相应控件的。所以给这些控件初始化话的时候一定要在布局加载之后，那么这里应该这么写，而且你得确保你的activity_main布局中是存在这些相应控件的    private Switch mBluetooh ;
    private Button aBluetooh ;
    private Button search ;
    private TextView humidity ;
    private Button button ;
    private ListView listView ;
    private TextView textView1;


protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    mBluetooh = findViewById(R.id.switch1);
        aBluetooh = findViewById(R.id.button2);
search = findViewById(R.id.button);
humidity = findViewById(R.id.textView5);
button = findViewById(R.id.button3);
listView = findViewById(R.id.listView);;
textView1 = findViewById(R.id.textView1);

}

Answer 18

肯定不是这里报错了...再贴日志.....然后你findviewbyid都不强制类型转换都不报错么....

Answer 19

05/17 10:32:45: Launching app
$ adb install-multiple -r -t -p com.example.a37061.myapplication D:\file\SKS\app\build\intermediates\split-apk\debug\slices\slice_9.apk D:\file\SKS\app\build\intermediates\instant-run-apk\debug\app-debug.apk 
Split APKs installed
$ adb shell am start -n "com.example.a37061.myapplication/com.example.a37061.myapplication.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 17621 on device meizu-mx5-85GABM8FAX62
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
W/Zygote: mz_is_rooted false
I/art: Late-enabling -Xcheck:jni
E/System: stat file error, path is /data/app/com.example.a37061.myapplication-2/lib/arm64, exception is android.system.ErrnoException: stat failed: ENOENT (No such file or directory)
W/linker: /system/lib64/libfilterUtils.so: unused DT entry: type 0x6ffffffe arg 0x808
          /system/lib64/libfilterUtils.so: unused DT entry: type 0x6fffffff arg 0x2
I/InstantRun: starting instant run server: is main process
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.example.a37061.myapplication, PID: 17621
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.a37061.myapplication/com.example.a37061.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Switch.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2685)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2754)
                      at android.app.ActivityThread.access$900(ActivityThread.java:187)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1584)
                      at android.os.Handler.dispatchMessage(Handler.java:111)
                      at android.os.Looper.loop(Looper.java:194)
                      at android.app.ActivityThread.main(ActivityThread.java:5898)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at java.lang.reflect.Method.invoke(Method.java:372)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Switch.setOnCheckedChangeListener(android.widget.CompoundButton$OnCheckedChangeListener)' on a null object reference
                      at com.example.a37061.myapplication.MainActivity.onCreate(MainActivity.java:65)
                      at android.app.Activity.performCreate(Activity.java:6127)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1125)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2638)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2754) 
                      at android.app.ActivityThread.access$900(ActivityThread.java:187) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1584) 
                      at android.os.Handler.dispatchMessage(Handler.java:111) 
                      at android.os.Looper.loop(Looper.java:194) 
                      at android.app.ActivityThread.main(ActivityThread.java:5898) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at java.lang.reflect.Method.invoke(Method.java:372) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1019) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:814) 
I/Process: Sending signal. PID: 17621 SIG: 9
Application terminated.
这是所有的了
public class MainActivity extends AppCompatActivity {
    private TextView humidity;
    private Button button;
    private ListView listView;
    private TextView textView1;    private BluetoothAdapter adpter = BluetoothAdapter.getDefaultAdapter();
    private static final String TAG = "MainActivity";
    private List<BluetoothDevice> mBlueList = new ArrayList<>();
    private final static int SEARCH_CODE = 0x123;
    private static final UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Switch bswitch = findViewById(R.id.switch1);
        Button Bbutton = findViewById(R.id.button2);
        Button search = findViewById(R.id.button);
        humidity = findViewById(R.id.textView5);
        button = findViewById(R.id.button3);
        listView = findViewById(R.id.listView);
        textView1 = findViewById(R.id.textView1);
        setContentView(R.layout.activity_main);

Answer 20

package com.example.a37061.myapplication;
import android.annotation.SuppressLint;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.app.ProgressDialog;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothSocket;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.CompoundButton;
import android.widget.ListView;
import android.widget.Switch;
import android.widget.TextView;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
public class MainActivity extends AppCompatActivity {
    private TextView humidity;
    private Button button;
    private ListView listView;
    private TextView textView1;    private BluetoothAdapter adpter = BluetoothAdapter.getDefaultAdapter();
    private static final String TAG = "MainActivity";
    private List<BluetoothDevice> mBlueList = new ArrayList<>();
    private final static int SEARCH_CODE = 0x123;
    private static final UUID uuid = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Switch bswitch = findViewById(R.id.switch1);
        Button Bbutton = findViewById(R.id.button2);
        Button search = findViewById(R.id.button);
        humidity = findViewById(R.id.textView5);
        button = findViewById(R.id.button3);
        listView = findViewById(R.id.listView);
        textView1 = findViewById(R.id.textView1);
        setContentView(R.layout.activity_main);        if (adpter == null) {
            //不支持蓝牙
            Log.i("bluetooh", "该手机不支持蓝牙");
            setTitle("该手机不支持蓝牙");
            return;
        }        //为开关绑定监听器
        bswitch.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean b) {
                if (b) {
                    // 开启switch
                    adpter.enable();
                    setTitle("蓝牙已经打开");
                } else {
                    //关闭switch
                    adpter.disable();
                    setTitle("蓝牙已经关闭");
                }
            }
        });

Answer 21

在我写连接和数据交互的这段程序前都能用，但是写完以后，switch就开始报空指针了

Answer 22

你switch对象为空啊,查查看你的XML是否有这个ID的swich控件,提示你无法setOnCheckedChangeListener在一个空对象上

Answer 23

找到错误了，findByID要放在set后面

Answer 24

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    MyAdapter adapter = new MyAdapter(MainActivity.this, mBlueList);
                    BluetoothDevice device = (BluetoothDevice) adapter.getItem(position);
                    connectDevice(device);
                }
            });
点击列表项以后怎么没用

Answer 25

@Jing丶无双