用Android studio 编程然后在夜神上显示MyApplication已停止运行


activity：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center_horizontal"
    android:orientation="vertical">
    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="打开普通对话框"
        android:textSize="20sp"/>    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="打开计算器对话框"
        android:textSize="20sp"/></LinearLayout>login：
<?xml version="1.0" encoding="utf-8"?>
    <GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:rowCount="6"
        android:columnCount="4">        <TextView        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_columnSpan="4"
        android:layout_marginLeft="4px"
       android:gravity="left"
       android:text="0"
       android:textSize="50dip"/>        <Button
            android:layout_columnSpan="4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="清除"/>    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="2"/>    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="3" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="4" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="5" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="6" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="7" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="8" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="9" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="*" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="." />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="=" />    <Button        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="/" />  </GridLayout>Java：
package com.example.pc.myapplication;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;public class MainActivity extends AppCompatActivity {    Button btn1,btn2;
    LinearLayout login;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn1=(Button)findViewById(R.id.button1);
        btn2=(Button)findViewById(R.id.button2);
        btn1.setOnClickListener(new mClick());
        btn2.setOnClickListener(new mClick());
    }
    class mClick implements OnClickListener{
        Builder dialog=new AlertDialog.Builder(MainActivity.this);
        @Override
        public void onClick(View arg0){
            if (arg0==btn1){
                dialog.setTitle("警告");
                dialog.setIcon(R.drawable.icon1);
                dialog.setMessage("本项操作可能导致信息泄露！");
                dialog.setPositiveButton("确定",new okClick());
                dialog.create();
                dialog.show();
            }
            else if(arg0==btn2){
                login=(LinearLayout)getLayoutInflater().inflate(R.layout.login,null);
                dialog.setTitle("计算器页面");
                dialog.setIcon(R.drawable.icon2);
                dialog.setNegativeButton("退出",new exitClick());
            }
        }
    }
    class okClick implements DialogInterface.OnClickListener{
        @Override
        public void onClick(DialogInterface dialog,int which){
            dialog.cancel();
        }
    }    class exitClick implements DialogInterface.OnClickListener{
        @Override
        public void onClick(DialogInterface dialog,int which){
            MainActivity.this.finish();
        }
    }能运行。但是打不开计算器界面