Android 停止 Runnable onBackPressed()

Question

我有一个使用处理程序的可运行间隔，它控制我的 Volley 请求:

final Handler handler = new Handler();

Runnable runnable = new Runnable() {
   @Override
   public void run() {

     //Volley request...
     AppController.getInstance().addToRequestQueue(volleyreq);

     handler.postDelayed(this, 5000);
   }
};

handler.postDelayed(runnable, 5000);

我需要在用户按下后退按钮并确认对话框时停止我的请求。这会停止我的位置更新、“检查”用户并切换到 CheckinActivity。我能否在此时以某种方式插入 removeCallbacks() 方法，或者它究竟会去哪里？

onBackPressed():

//Checking Out With Back Button
public void onBackPressed() {

  AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(this);

  alertDialogBuilder.setTitle("Checking Out!");
  alertDialogBuilder.setMessage("Are you sure you want to check out?");
  alertDialogBuilder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
      @Override
      public void onClick(DialogInterface dialog, int which) {
        //Inserting here crashes app after pressing back button
        handler.removeCallbacks(runnable);

        //Disconnects from location updates...
        mGoogleApiClient.disconnect();

        //Fires a volley POST request...
        checkout();

        Intent intent=new Intent(OrderListActivity.this,CheckinActivity.class);
        startActivity(intent);

        OrderListActivity.this.finish();

      }
  });

  alertDialogBuilder.setNegativeButton("No", new DialogInterface.OnClickListener() {
      @Override
      public void onClick(DialogInterface dialog, int which) {
        dialog.cancel();
      }
  });

  AlertDialog alertDialog = alertDialogBuilder.create();
  alertDialog.show();

}

我试过从不同的地方触发它，但它总是让我的应用程序崩溃并给我一个空指针异常。

崩溃日志:

08-20 19:41:08.540 2815-2815/com.myapp.workingprojectlocal E/AndroidRuntime: FATAL EXCEPTION: main
                                                                               Process: com.myapp.workingprojectlocal, PID: 2815
                                                                               java.lang.NullPointerException: Attempt to invoke virtual method 'void android.os.Handler.removeCallbacks(java.lang.Runnable)' on a null object reference
                                                                                   at com.myapp.workingprojectlocal.OrderListActivity$12.onClick(OrderListActivity.java:394)
                                                                                   at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:161)
                                                                                   at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                   at android.os.Looper.loop(Looper.java:154)
                                                                                   at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                                                   at java.lang.reflect.Method.invoke(Native Method)
                                                                                   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

这意味着您的处理程序是 NULL。这样做:

if (handler !=null && runnable !=null)
   handler.removeCallbacks(runnable);

它应该可以解决您的问题。