Java 从另一个线程和类中取消进度对话框

我有一个单独的AsyncTask类，它执行一些耗时的任务。从活动调用AsyncTask时，将启动进度对话框。如果用户取消对话框或在执行后台任务时发生错误，则会取消该对话框。如果后台进程成功，它应该运行verifyingUser方法，因为这是主要活动。这就是我的问题所在。这是我的密码：

 public class CreateAccountTask extends AsyncTask<String, Void, String>{

 private ProgressDialog mpDialog;
 private CreateAccountTask task; 
 private Context context;
 private Activity activity;
 private CreateAccount createAccount;
 private AsyncTaskListener asyncTaskListener;


 public CreateAccountTask(Activity activity, AsyncTaskListener asyncTaskListener){

this.activity = activity;
this.asyncTaskListener = asyncTaskListener;
}


@Override
protected void onPreExecute() {
    // TODO Auto-generated method stub
    super.onPreExecute();

    mpDialog = new ProgressDialog(activity);

    //mpDialog.setTitle("Creating Account");
    mpDialog.setMessage("Please wait.");
    mpDialog.setCancelable(false);
    mpDialog.setIndeterminate(false);
    mpDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "CANCEL", new      DialogInterface.OnClickListener() {

        @Override
        public void onClick(DialogInterface arg0, int arg1) {
            // TODO Auto-generated method stub
            //task.cancel(true);
            mpDialog.dismiss();

        }
    });

    mpDialog.show();

}


@Override
protected String doInBackground(String... arg0) {
// TODO Auto-generated method stub

String fphoneNo = arg0[1];
String fpassword = arg0[0];

// create instance of the parseUser Class
ParseUser newUser = new ParseUser();
newUser.setUsername(fphoneNo);
newUser.setPassword(fpassword);

// here Check if progress dialog has been cancelled

if (!isCancelled()){

// if dialog has not been cancelled create the new user here
newUser.signUpInBackground(new SignUpCallback() {

    @Override
    public void done(ParseException e) {

              // Something went wrong Sorry!

        if(e != null ){


            if(!isCancelled()){
            mpDialog.dismiss();

            String errorMessage = e.getMessage().toString();

            ErrorHappened(errorMessage);

            }

            else{

                String errorMessage = "Registration Cancelled!";
                ErrorHappened(errorMessage);

            }

        }

        // No Problems 
        else {
            if (!isCancelled()) {

                // Wait for five seconds before starting the activity
                //verifyingUser();

            }
            else {
                String errorMessage = "Registration Cancelled2!";
                ErrorHappened(errorMessage);

                //Delete user in background
                ParseUser currentUser = ParseUser.getCurrentUser();
                if (currentUser != null) {
                    currentUser.deleteInBackground();
                }

            }
        }   

        }

                });

}

return null;
}

@Override
protected void onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
asyncTaskListener.onTaskComplete(result);
}

private void ErrorHappened(String errorMessage) {

Crouton CreateMagic = Crouton.makeText(createAccount, errorMessage, CroutonClass.ALERT);
CreateMagic.setConfiguration(CroutonClass.configure);
CreateMagic.show();


}

}

当它试图关闭对话框时，我会遇到此异常：

 03-05 13:43:32.839: E/AndroidRuntime(21782): FATAL EXCEPTION: main
 03-05 13:43:32.839: E/AndroidRuntime(21782): java.lang.NullPointerException
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.content.ComponentName.<init>  (ComponentName.java:75)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.content.Intent.<init>(Intent.java:3655)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount.ok(CreateAccount.java:527)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount$3.done(CreateAccount.java:480)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount$3.done(CreateAccount.java:1)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.parse.FunctionCallback.internalDone(FunctionCallback.java:44)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.parse.Parse$6$1.run(Parse.java:834)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Handler.handleCallback(Handler.java:615)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Handler.dispatchMessage(Handler.java:92)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Looper.loop(Looper.java:155)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.app.ActivityThread.main(ActivityThread.java:5454)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at java.lang.reflect.Method.invokeNative(Native Method)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at java.lang.reflect.Method.invoke(Method.java:511)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at dalvik.system.NativeStart.main(Native Method)

---

如何从verifyingUser方法中取消对话框

您正试图修改工作线程中的UI组件。您必须在onPostExecute中或在主线程中执行此操作。您可以做的是取消任务或返回null或某些标志值，然后取消onPostExecute

---

第527行@CreateAccount是什么？它是一个包含CreateAccountTask.mpDialog.Disclose的ok方法；我要取消对话框的地方。你也发布了代码吗？如果没有，请发布该方法。您有ComponentName类吗？如果没有，您确定要取消初始化对话框吗？没有，我没有ComponentName类。在其他类中创建对话框时，如何在活动中初始化对话框。

 03-05 13:43:32.839: E/AndroidRuntime(21782): FATAL EXCEPTION: main
 03-05 13:43:32.839: E/AndroidRuntime(21782): java.lang.NullPointerException
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.content.ComponentName.<init>  (ComponentName.java:75)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.content.Intent.<init>(Intent.java:3655)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount.ok(CreateAccount.java:527)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount$3.done(CreateAccount.java:480)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.example.razcat.CreateAccount$3.done(CreateAccount.java:1)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.parse.FunctionCallback.internalDone(FunctionCallback.java:44)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.parse.Parse$6$1.run(Parse.java:834)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Handler.handleCallback(Handler.java:615)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Handler.dispatchMessage(Handler.java:92)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.os.Looper.loop(Looper.java:155)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at android.app.ActivityThread.main(ActivityThread.java:5454)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at java.lang.reflect.Method.invokeNative(Native Method)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at java.lang.reflect.Method.invoke(Method.java:511)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1029)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:796)
 03-05 13:43:32.839: E/AndroidRuntime(21782):   at dalvik.system.NativeStart.main(Native Method)