Java 应用程序因消息“而崩溃”；不幸的是，该项目已经停止。”；关于；OnClick"；听众

当我在Eclipse中的AVD中运行应用程序时，它工作正常，直到我单击Add按钮：应用程序被一条消息停止。不幸的是，项目已经停止。我对安卓系统很陌生，所以，我可能犯了一些愚蠢的错误。请检查一下这个密码，把我从这场危机中解救出来

MainActivity.java

MyOnClickListener.java

activity_main.xml

---

您需要一个

上下文

引用。创建

类时，可以显式传递为参数。所以你的代码应该是

公共类MyOnClickListener扩展了MainActivity实现OnClickListener{

MainActivity caller;
public MyOnClickListener(MainActivity activity) {
this.caller = activity;
}
public void onClick(View view) {
    num1 = Double.parseDouble(val1.getText().toString());
    num2 = Double.parseDouble(val2.getText().toString());
    res = num1 + num2;
    Toast.makeText(caller, String.valueOf(res), Toast.LENGTH_SHORT).show();
}

}

当从
val1
变量
EditText
获取
num1
值时，您得到了EditText的
null对象引用。因此，请使用
调用者访问此变量

public void onClick(View view) {
        num1 = Double.parseDouble(caller.val1.getText().toString());
        num2 = Double.parseDouble(caller.val2.getText().toString());
        res = num1 + num2;
        Toast.makeText(caller, String.valueOf(res), Toast.LENGTH_SHORT).show();
}

您可以获得
val1
和
val2
值，并可以实现
按钮
侦听器是这样的同一类

  public class MainActivity extends Activity {

     Button button,btnAdd,btnSub;
     EditText val1,val2;

    double num1,num2,res;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        val1 = (EditText) findViewById(R.id.txtVal1);
        val2 = (EditText) findViewById(R.id.txtVal2);
        btnAdd = (Button) findViewById(R.id.btnSum);
        btnSub = (Button) findViewById(R.id.btnDiff);

        btnAdd.setOnClickListener(new OnClickListener(){

          public void onClick(View view) {
              num1 = Double.parseDouble(val1.getText().toString());
              num2 = Double.parseDouble(val2.getText().toString());
              res = num1 + num2;
              Toast.makeText(MainActivity.this, String.valueOf(res), Toast.LENGTH_SHORT).show();
              }
          });
       }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

崩溃日志是什么toast中MyOclicListener类的Just use上下文..如果我也需要调用btnSub.setOnCliCkListner（新OnClickListener），我如何调用它case@SarojShrestha首先，您必须添加
btnSub
单击
main活动中的listner
like
btnSub.setOnClickListener（新的MyOnClickListener（此））
。然后在
MyOnClickListener
类中，您必须使用switch case，在这种情况下，您可以通过Id访问：
btnSub.setOnClickListener（新的MyOnClickListener（this））；
和`switch（view.getId（））{case R.id.btnSum://old code break；case R.id.btnDiff:Toast.makeText（调用方，“Diff called”，Toast.LENGTH_SHORT）.show（）；break；}`
07-13 01:02:24.800: D/(972): HostConnection::get() New Host Connection established 0xb8b52560, tid 972
07-13 01:02:24.930: W/EGL_emulation(972): eglSurfaceAttrib not implemented
07-13 01:02:24.960: D/OpenGLRenderer(972): Enabling debug mode 0
07-13 01:02:42.092: D/AndroidRuntime(972): Shutting down VM
07-13 01:02:42.092: W/dalvikvm(972): threadid=1: thread exiting with uncaught exception (group=0xb3aa3b90)
07-13 01:02:42.152: E/AndroidRuntime(972): FATAL EXCEPTION: main
07-13 01:02:42.152: E/AndroidRuntime(972): Process: com.example.firstproject, PID: 972
07-13 01:02:42.152: E/AndroidRuntime(972): java.lang.NullPointerException
07-13 01:02:42.152: E/AndroidRuntime(972):  at com.example.firstproject.MyOnClickListener.onClick(MyOnClickListener.java:14)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.view.View.performClick(View.java:4424)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.view.View$PerformClick.run(View.java:18383)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.os.Handler.handleCallback(Handler.java:733)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.os.Handler.dispatchMessage(Handler.java:95)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.os.Looper.loop(Looper.java:137)
07-13 01:02:42.152: E/AndroidRuntime(972):  at android.app.ActivityThread.main(ActivityThread.java:4998)
07-13 01:02:42.152: E/AndroidRuntime(972):  at java.lang.reflect.Method.invokeNative(Native Method)
07-13 01:02:42.152: E/AndroidRuntime(972):  at java.lang.reflect.Method.invoke(Method.java:515)
07-13 01:02:42.152: E/AndroidRuntime(972):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
07-13 01:02:42.152: E/AndroidRuntime(972):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
07-13 01:02:42.152: E/AndroidRuntime(972):  at dalvik.system.NativeStart.main(Native Method)

MainActivity caller;
public MyOnClickListener(MainActivity activity) {
this.caller = activity;
}
public void onClick(View view) {
    num1 = Double.parseDouble(val1.getText().toString());
    num2 = Double.parseDouble(val2.getText().toString());
    res = num1 + num2;
    Toast.makeText(caller, String.valueOf(res), Toast.LENGTH_SHORT).show();
}

}

public void onClick(View view) {
        num1 = Double.parseDouble(caller.val1.getText().toString());
        num2 = Double.parseDouble(caller.val2.getText().toString());
        res = num1 + num2;
        Toast.makeText(caller, String.valueOf(res), Toast.LENGTH_SHORT).show();
}

  public class MainActivity extends Activity {

     Button button,btnAdd,btnSub;
     EditText val1,val2;

    double num1,num2,res;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        val1 = (EditText) findViewById(R.id.txtVal1);
        val2 = (EditText) findViewById(R.id.txtVal2);
        btnAdd = (Button) findViewById(R.id.btnSum);
        btnSub = (Button) findViewById(R.id.btnDiff);

        btnAdd.setOnClickListener(new OnClickListener(){

          public void onClick(View view) {
              num1 = Double.parseDouble(val1.getText().toString());
              num2 = Double.parseDouble(val2.getText().toString());
              res = num1 + num2;
              Toast.makeText(MainActivity.this, String.valueOf(res), Toast.LENGTH_SHORT).show();
              }
          });
       }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}