Android：不幸的是，该应用已停止

Question

I am a beginner with Android, trying to run my first application. But there's an error in the log file and application get terminated by this message "Unfortunately, app has stopped"!

Here is my java file:

public class MainActivity extends ActionBarActivity {

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

    Button mClick=(Button)findViewById(R.id.button1);

    mClick.setOnClickListener(new View.OnClickListener() {


    //@Override
    @SuppressLint("ShowToast")
    public void onClick(View v) {
        // TODO Auto-generated method stub
        Toast t = Toast.makeText(MainActivity.this, R.string.hi, 3000).show();          

    }
            });
}
}

And the log has these errors:

04-19 18:50:02.200: E/AndroidRuntime(792): FATAL EXCEPTION: main
04-19 18:50:02.200: E/AndroidRuntime(792): Process: com.example.test, PID: 792
04-19 18:50:02.200: E/AndroidRuntime(792): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.MainActivity}: java.lang.NullPointerException
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.os.Handler.dispatchMessage(Handler.java:102)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.os.Looper.loop(Looper.java:136)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread.main(ActivityThread.java:5017)
04-19 18:50:02.200: E/AndroidRuntime(792):  at java.lang.reflect.Method.invokeNative(Native Method)
04-19 18:50:02.200: E/AndroidRuntime(792):  at java.lang.reflect.Method.invoke(Method.java:515)
04-19 18:50:02.200: E/AndroidRuntime(792):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-19 18:50:02.200: E/AndroidRuntime(792):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-19 18:50:02.200: E/AndroidRuntime(792):  at dalvik.system.NativeStart.main(Native Method)
04-19 18:50:02.200: E/AndroidRuntime(792): Caused by: java.lang.NullPointerException
04-19 18:50:02.200: E/AndroidRuntime(792):  at com.example.test.MainActivity.onCreate(MainActivity.java:29)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.Activity.performCreate(Activity.java:5231)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-19 18:50:02.200: E/AndroidRuntime(792):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
04-19 18:50:02.200: E/AndroidRuntime(792):  ... 11 more

Can you spot the problem?

Answer 1

Your mClick button is not being created, probably because findViewById(R.id.button1) is failing.

Then, because the button is null, when you call a function on it you get a NPE.

Answer 2

mClick is probably null. Check if R.id.button1 exists in the layout you set on setContentView.