Android：不幸的是应用已停止

Question

I am trying make an app that uses the accelerometer but when I run my app it says unfortunately app has stopped. I had other code but i deleted it because i thought it was messing up the code but it wasn't.

Here is the code

`

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Intent one = new Intent(getApplicationContext(), act.class);
    startActivity(one);


}


        }
          class act extends Activity implements SensorEventListener {
              Intent one = getIntent();
              private SensorManager sensorManager;
                private Sensor accelerometer;
             float x,y,z;   
             @Override
             public void onCreate(Bundle savedInstanceState) {
                    super.onCreate(savedInstanceState);

                    setContentView(R.layout.activity2);
                    sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
                    accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
             }

             protected void onResume() {
                    super.onResume();
                    sensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_NORMAL);
                }
                protected void onPause() {
                    super.onPause();
                    sensorManager.unregisterListener(this);
                }


           @Override
           public void onAccuracyChanged(Sensor accelerometer, int accuracy) {
           }
             public void onSensorChanged(SensorEvent event) {

                    if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {

                        x = event.values[0];
                        y = event.values[1];
                        z = event.values[2];

                    }
                        }

             }`

Both of the classes are in the same file

LogCat:

02-19 14:32:24.490: E/AndroidRuntime(7916): FATAL EXCEPTION: main
02-19 14:32:24.490: E/AndroidRuntime(7916): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.a3/com.example.a3.MainActivity}: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.a3/com.example.a3.act}; have you declared this activity in your AndroidManifest.xml?
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.os.Handler.dispatchMessage(Handler.java:99)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.os.Looper.loop(Looper.java:137)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread.main(ActivityThread.java:5039)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at java.lang.reflect.Method.invokeNative(Native Method)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at java.lang.reflect.Method.invoke(Method.java:511)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at dalvik.system.NativeStart.main(Native Method)
02-19 14:32:24.490: E/AndroidRuntime(7916): Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.a3/com.example.a3.act}; have you declared this activity in your AndroidManifest.xml?
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1618)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Instrumentation.execStartActivity(Instrumentation.java:1417)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Activity.startActivityForResult(Activity.java:3370)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Activity.startActivityForResult(Activity.java:3331)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Activity.startActivity(Activity.java:3566)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Activity.startActivity(Activity.java:3534)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at com.example.a3.MainActivity.onCreate(MainActivity.java:32)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Activity.performCreate(Activity.java:5104)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
02-19 14:32:24.490: E/AndroidRuntime(7916):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
02-19 14:32:24.490: E/AndroidRuntime(7916):     ... 11 more

Answer 1

Chances are you did not declare the act activity correctly in the manifest. Run android lint on your project, and see if it tells you what's happening. Or in Eclipse look at your manifest file in all the manifest viewer tabs (not just code) and see if it gives you red warnings.