Android应用程序崩溃..意图标志？

Question

我的应用最近发生了一些崩溃，我想知道这是否可能是由于意图上的标志造成的。

当崩溃发生时，我相信应用程序会在休息计时器期间关闭。打开一个片段，然后用户可以单击开始，这将启动一个 90 秒的倒计时。计时器结束时，用户会收到通知，单击该通知时应将用户带回打开的片段。该错误不会经常发生，我无法每次都重新创建它。

这是堆栈跟踪：

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ComponentName.<init>(ComponentName.java:77)
at android.content.Intent.<init>(Intent.java:4913)
at com.bestworkouts.sheikoworkout.Workouts.Week1Mon.showNotification(Week1Mon.java:171)
at com.bestworkouts.sheikoworkout.Workouts.Week1Mon$1.onFinish(Week1Mon.java:147)
at android.os.CountDownTimer$1.handleMessage(CountDownTimer.java:127)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6938)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)

这是错误所在的通知（它说错误在 Intent intent = new Intent(getActivity(), MyWorkout.class)：

public void showNotification() {
    NotificationCompat.Builder builder = new NotificationCompat.Builder(getContext());
    builder.setSmallIcon(R.drawable.sheikoicon);
    builder.setContentTitle("Sheiko Rest Timer");
    builder.setContentText("Rest timer is up, start your set!");
    builder.setDefaults(Notification.DEFAULT_SOUND|Notification.DEFAULT_VIBRATE);
    builder.setAutoCancel(true);
    Intent intent = new Intent(getActivity(), MyWorkout.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    TaskStackBuilder stackBuilder = TaskStackBuilder.create(getContext());
    stackBuilder.addParentStack(MyWorkout.class);
    stackBuilder.addNextIntent(intent);
    PendingIntent pendingIntent = stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);
    builder.setContentIntent(pendingIntent);
    NotificationManager NM = (NotificationManager) getActivity().getSystemService(Context.NOTIFICATION_SERVICE);
    NM.notify(0, builder.build());
}

我在哪里启动倒数计时器并调用 showNotification：

private void start() {
    cancel();
    mCountDownTimer = new CountDownTimer(90000, 1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            txtViewRest.setText(millisUntilFinished / 1000 + " Secs");
        }

        @Override
        public void onFinish() {
            txtViewRest.setText("Start!");
            showNotification();
        }
    }.start();
}

我想知道这是否与我的 FLAG_ACTIVITY_CLEAR_TOP 有关？

感谢您的帮助！

Answer 1

由于您的代码在另一个线程上运行，如果在 CountDownTimer 完成时 Fragment 已因任何原因关闭，getActivity() 和 getContext() 都将返回 null。

您应该将上下文保存在Fragment 的onCreate 中：

private Context context;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    context= getContext();

    // Your code here

}

然后在 showNotification() 方法中使用它：

public void showNotification() {
    NotificationCompat.Builder builder = new NotificationCompat.Builder(context);
    builder.setSmallIcon(R.drawable.sheikoicon);
    builder.setContentTitle("Sheiko Rest Timer");
    builder.setContentText("Rest timer is up, start your set!");
    builder.setDefaults(Notification.DEFAULT_SOUND|Notification.DEFAULT_VIBRATE);
    builder.setAutoCancel(true);
    Intent intent = new Intent(context, MyWorkout.class);
    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    TaskStackBuilder stackBuilder = TaskStackBuilder.create(context);
    stackBuilder.addParentStack(MyWorkout.class);
    stackBuilder.addNextIntent(intent);
    PendingIntent pendingIntent = stackBuilder.getPendingIntent(0, PendingIntent.FLAG_UPDATE_CURRENT);
    builder.setContentIntent(pendingIntent);
    NotificationManager NM = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    NM.notify(0, builder.build());
}