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我正在开发一个应用程序，它包含一个实现ViewPager和3个片段的MainActivity。我定义了MainActivity中的所有逻辑方法，这些片段只是实现了UI引用的方法。当触摸屏停止mediaplayer
所以在MainActivity我有一个方法，其中一些hapens并开始在MediaPlayer这样：
mp = MediaPlayer.create(MainActivity.this, R.raw.alarm);
try {
mp.setLooping(true);
} catch (IllegalStateException e) {
e.printStackTrace();
}
mp.start();
这得到播放的声音进入一个循环。现在，我需要能够阻止它只是触摸屏，我已经实现了的onTouchEvent（）方法是这样的：
@Override
public boolean onTouchEvent (MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
/*If sound is playing, stops*/
if (mp.isPlaying()) {
mp.stop();
}
return true;
}
return super.onTouchEvent(event);
}
这里是问题。我无法让声音停止，所以我想上面的方法不起作用。 SO成员已经要求我使用dispatchTouchEvent()而不是onTouchEvent()，但这样做会强制关闭应用程序，而不会在LogCat中引发任何错误消息。
@Override
public boolean dispatchTouchEvent (MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
/*If sound is playing, stops*/
if (mp.isPlaying()) {
mp.stop();
}
return true;
}
return super.dispatchTouchEvent(event);
}
所以我不知道那个方法有什么问题。或者，也许问题可能是这必须在每个片段而不是MainAcitivity中实现？
更新
我与日食的问题，它dind't显示logcat的信息，但现在就解决了，这就是它抛出：
09-01 16:43:15.591: E/InputEventReceiver(30873): Exception dispatching input event.
09-01 16:43:15.591: E/MessageQueue-JNI(30873): Exception in MessageQueue callback: handleReceiveCallback
09-01 16:43:15.591: E/MessageQueue-JNI(30873): java.lang.NullPointerException
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at com.itest.MainActivity.dispatchTouchEvent(MainActivity.java:818)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.support.v7.app.ActionBarActivityDelegateICS$WindowCallbackWrapper.dispatchTouchEvent(ActionBarActivityDelegateICS.java:260)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2228)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.View.dispatchPointerEvent(View.java:8315)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4596)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4464)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4076)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4045)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4156)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4053)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4213)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4076)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4045)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4053)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6403)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6307)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6278)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6243)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6483)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.os.MessageQueue.nativePollOnce(Native Method)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.os.MessageQueue.next(MessageQueue.java:138)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.os.Looper.loop(Looper.java:123)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at android.app.ActivityThread.main(ActivityThread.java:5356)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at java.lang.reflect.Method.invokeNative(Native Method)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at java.lang.reflect.Method.invoke(Method.java:515)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
09-01 16:43:15.591: E/MessageQueue-JNI(30873): at dalvik.system.NativeStart.main(Native Method)
09-01 16:43:15.591: D/AndroidRuntime(30873): Shutting down VM
09-01 16:43:15.601: W/dalvikvm(30873): threadid=1: thread exiting with uncaught exception (group=0x4180bda0)
09-01 16:43:15.601: E/AndroidRuntime(30873): FATAL EXCEPTION: main
09-01 16:43:15.601: E/AndroidRuntime(30873): Process: com.itest, PID: 30873
09-01 16:43:15.601: E/AndroidRuntime(30873): java.lang.NullPointerException
09-01 16:43:15.601: E/AndroidRuntime(30873): at com.itest.MainActivity.dispatchTouchEvent(MainActivity.java:818)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.support.v7.app.ActionBarActivityDelegateICS$WindowCallbackWrapper.dispatchTouchEvent(ActionBarActivityDelegateICS.java:260)
09-01 16:43:15.601: E/AndroidRuntime(30873): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2228)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.View.dispatchPointerEvent(View.java:8315)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4596)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4464)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4076)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4045)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4156)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4053)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4213)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4076)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4045)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4053)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4022)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6403)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6307)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6278)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6243)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6483)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.os.MessageQueue.nativePollOnce(Native Method)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.os.MessageQueue.next(MessageQueue.java:138)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.os.Looper.loop(Looper.java:123)
09-01 16:43:15.601: E/AndroidRuntime(30873): at android.app.ActivityThread.main(ActivityThread.java:5356)
09-01 16:43:15.601: E/AndroidRuntime(30873): at java.lang.reflect.Method.invokeNative(Native Method)
09-01 16:43:15.601: E/AndroidRuntime(30873): at java.lang.reflect.Method.invoke(Method.java:515)
09-01 16:43:15.601: E/AndroidRuntime(30873): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
09-01 16:43:15.601: E/AndroidRuntime(30873): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
09-01 16:43:15.601: E/AndroidRuntime(30873): at dalvik.system.NativeStart.main(Native Method)
凡在MainActivity线818指的onTouchEvent（）或dispatchTouchEvent（）方法，正是这条线：
if (mp.isPlaying()) {
What's line MainActivity.java:818？它引发NPE – 2014-09-02 11:48:12
@Dhruti，问题更新 – masmic 2014-09-02 11:48:49
查看答案。 “mp”最初可能为空。把条件处理。你已经完成:) – 2014-09-02 11:52:54