android - CountDownTimer 不会让我调用 onDestroy

Question

我已经制作了简单的倒数计时器应用程序，但是当我尝试让 onDestroy 取消倒数计时器时，我得到了错误。我的 onDestroy 代码块:

    @Override
    public void onDestroy()
    {
    super.onDestroy();
    countdowntimer.cancel();
    }

和 LogCat 错误

12-18 19:16:06.383: E/AndroidRuntime(25512): FATAL EXCEPTION: main
12-18 19:16:06.383: E/AndroidRuntime(25512): java.lang.RuntimeException: Unable to destroy        activity {com.android.SquirellMusic/com.android.SquirellMusic.SquirellMusicActivity}: java.lang.NullPointerException
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3106)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3171)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread.access$2100(ActivityThread.java:132)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1071)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.os.Handler.dispatchMessage(Handler.java:99)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at      android.os.Looper.loop(Looper.java:150)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread.main(ActivityThread.java:4293)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at java.lang.reflect.Method.invokeNative(Native Method)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at java.lang.reflect.Method.invoke(Method.java:507)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:849)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:607)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at dalvik.system.NativeStart.main(Native Method)
12-18 19:16:06.383: E/AndroidRuntime(25512): Caused by: java.lang.NullPointerException
12-18 19:16:06.383: E/AndroidRuntime(25512):    at com.android.SquirellMusic.SquirellMusicActivity.onDestroy(SquirellMusicActivity.java:364)
12-18 19:16:06.383: E/AndroidRuntime(25512):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3088)

感谢任何帮助

Answer 1

答案在于 Activity 的 onDestroy() 的以下概念:

• onDestroy() 由 DVM 自动调用。在此之后， Activity 将从堆栈中删除。

现在，您的 countdowntimer.cancel 代码是在 super() 之后编写的，因此 Activity (连同您的 countdowntimer 对象)在您的 countdowntimer.cancel 之前从内存中删除。

因此只需将 super.onDestroy() 移动到 onDestroy() 方法的末尾即可避免应用程序崩溃。