从父活动调用autoFocus()返回NPE

Question

我已经实例化了一个扩展CameraFragment (并实现TabListener)的片段类型，并且我正在尝试从父活动调用autoFocus()。从扩展CameraFragment的片段调用autoFocus()可以很好地工作，但从父活动调用它会导致NPE。我正在监听main活动中的onKeyDown()事件，它按照logcat的预期工作。这是我的NPE跟踪：

09-10 10:00:16.410: D/app(5283): onKeyDown: 80

09-10 10:00:16.415: D/AndroidRuntime(5283): Shutting down VM

09-10 10:00:16.415: W/dalvikvm(5283): threadid=1: thread exiting with uncaught exception (group=0x40f7b2a0)

09-10 10:00:16.425: E/AndroidRuntime(5283): FATAL EXCEPTION: main

09-10 10:00:16.425: E/AndroidRuntime(5283): java.lang.NullPointerException

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.commonsware.cwac.camera.CameraFragment.autoFocus(CameraFragment.java:96)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.me.app.appCameraFragment.callAutoFocus(cameraFragment.java:232)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.me.app.MainTabActivity.onKeyDown(MainTabActivity.java:264)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.view.KeyEvent.dispatch(KeyEvent.java:2705)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.app.Activity.dispatchKeyEvent(Activity.java:2423)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:2019)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.view.ViewRootImpl.deliverKeyEventPostIme(ViewRootImpl.java:3851)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.view.ViewRootImpl.handleImeFinishedEvent(ViewRootImpl.java:3799)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.view.ViewRootImpl$ViewRootHandler.handleMessage(ViewRootImpl.java:2934)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.os.Handler.dispatchMessage(Handler.java:99)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.os.Looper.loop(Looper.java:137)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at android.app.ActivityThread.main(ActivityThread.java:4921)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at java.lang.reflect.Method.invokeNative(Native Method)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at java.lang.reflect.Method.invoke(Method.java:511)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1036)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:803)

09-10 10:00:16.425: E/AndroidRuntime(5283):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

我不确定您正在处理的代码的版本是什么，但是第96行是当前CameraFragment中的右大括号。

对于NullPointerException，autoFocus()崩溃的唯一原因是如果cameraView为null，而cameraView应该为null的唯一原因是onCreateView()尚未被调用。在请求自动对焦之前，您需要片段可见并完全创建。