我的代码简单就是一个乘法器
moonTest.java 2个edittext输入,点击提交就跳到 ActResult.java显示结果!moonTest.javapublic class moonTest extends Activity {
/** Called when the activity is first created. */

private android.widget.EditText edx1;
private android.widget.EditText edx2;
private android.widget.TextView tv1;
private android.widget.Button btn1;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main); btn1 = (Button)findViewById(R.id.button1);
edx1 = (EditText)findViewById(R.id.edx1);
edx2 = (EditText)findViewById(R.id.edx2);
tv1 = (TextView)findViewById(R.id.txtview1); btn1.setOnClickListener( new btn1Linster());
}

class btn1Linster implements OnClickListener
{
@Override
public void onClick(View v) {
String fact1str = edx1.getText().toString();
String fact2str = edx2.getText().toString();
Intent intent = new Intent();
intent.putExtra("f1", fact1str);
intent.putExtra("f2", fact2str);
intent.setClass(moonTest.this, ActResult.class); //不明白这句话的意思
moonTest.this.startActivity(intent);
}

}
}
ActResult.javapackage com.moontest;
public class ActResult extends Activity{
private android.widget.TextView edx;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

edx = (android.widget.TextView )findViewById(R.id.resultview);

Intent intent = getIntent();
String fct1 = intent.getStringExtra("f1");
String fct2 = intent.getStringExtra("f2");
int fint1 = Integer.parseInt(fct1);
int fint2 = Integer.parseInt(fct2);
int intResult = fint1*fint2;

edx.setText(intResult+"");
}
}这句话去掉就正常,但是 加上 edx.setText(intResult+"");当点击计算的时候就出错了··
error如下,求指正啊大哥们
11-22 04:06:15.096: W/KeyCharacterMap(334): No keyboard for id 0
11-22 04:06:15.096: W/KeyCharacterMap(334): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
11-22 04:12:56.709: D/AndroidRuntime(370): Shutting down VM
11-22 04:12:56.709: W/dalvikvm(370): threadid=1: thread exiting with uncaught exception (group=0x40015560)
11-22 04:12:56.735: E/AndroidRuntime(370): FATAL EXCEPTION: main
11-22 04:12:56.735: E/AndroidRuntime(370): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.moontest/com.moontest.ActResult}: java.lang.NullPointerException
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.os.Looper.loop(Looper.java:123)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread.main(ActivityThread.java:3683)
11-22 04:12:56.735: E/AndroidRuntime(370):  at java.lang.reflect.Method.invokeNative(Native Method)
11-22 04:12:56.735: E/AndroidRuntime(370):  at java.lang.reflect.Method.invoke(Method.java:507)
11-22 04:12:56.735: E/AndroidRuntime(370):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-22 04:12:56.735: E/AndroidRuntime(370):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-22 04:12:56.735: E/AndroidRuntime(370):  at dalvik.system.NativeStart.main(Native Method)
11-22 04:12:56.735: E/AndroidRuntime(370): Caused by: java.lang.NullPointerException
11-22 04:12:56.735: E/AndroidRuntime(370):  at com.moontest.ActResult.onCreate(ActResult.java:23)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-22 04:12:56.735: E/AndroidRuntime(370):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
11-22 04:12:56.735: E/AndroidRuntime(370):  ... 11 more

解决方案 »

  1.   

    日志里面:
    11-22 04:12:56.735: E/AndroidRuntime(370): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.moontest/com.moontest.ActResult}: java.lang.NullPointerExceptionedx 为 null 了
      

  2.   

    因为你的乘法结果是整型,而显示在textview上面是字符串型,你必须把结果转化成字符串型,String。valuesOf(intResult),你试试对不对
      

  3.   

    ActResult.java
    package com.moontest;
    public class ActResult extends Activity{
        private android.widget.TextView edx;
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main); //检查你的main.xml布局文件中是否有resultview的定义
            
            edx = (android.widget.TextView )findViewById(R.id.resultview);
    //检查下这里的edx是否为null,如果是的话,检查上面那句
            
            Intent intent = getIntent();
            String fct1 = intent.getStringExtra("f1");
            String fct2 = intent.getStringExtra("f2");
            int fint1 = Integer.parseInt(fct1);
            int fint2 = Integer.parseInt(fct2);
            int intResult = fint1*fint2;
            
            edx.setText(intResult+"");
        }
    }
      

  4.   


    edx.setText(intResult+"");  所以我才 +""  转换为字符串!谢谢xuehai_sc!