如何從回調方法執行AsyncTask？

Question

我有一個代碼：

private void submitExec() { 

    if (SQLiteDbWrapper.getInstance().getBookCount()==0) { 

     Toast.makeText(this, "A list of books is empty", Toast.LENGTH_LONG).show(); 
     return; 
    } 

    SQLiteDbWrapper.getInstance().makeFacebook(this, this.getApplicationContext()); 
    if (SQLiteDbWrapper.getInstance().getConnector().getFacebook().isSessionValid()) { 
     new SubmitClass().execute(); 
    } 
    else { 

     SessionEvents.AuthListener listener = new SessionEvents.AuthListener() { 

      @Override 
      public void onAuthSucceed() { 
       MyBookDroidActivity.this.executeSubmitClass(); 
      } 

      @Override 
      public void onAuthFail(String error) { 

      } 
     }; 
     SessionEvents.addAuthListener(listener); 
     SQLiteDbWrapper.getInstance().getConnector().login(); 
    } 
} 

private void executeSubmitClass() { 

    new SubmitClass().execute(); 
} 

此代碼授權通過Facebook和執行的AsyncTask。但我得到運行時錯誤總是：

12-13 21:58:41.513: E/AndroidRuntime(31961): Uncaught handler: thread Thread-25 exiting due to uncaught exception 
12-13 21:58:41.523: E/AndroidRuntime(31961): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.os.Handler.<init>(Handler.java:121) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.app.Dialog.<init>(Dialog.java:105) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.app.AlertDialog.<init>(AlertDialog.java:63) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.app.ProgressDialog.<init>(ProgressDialog.java:80) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.app.ProgressDialog.<init>(ProgressDialog.java:76) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.mybookdroid.MyBookDroidActivity$SubmitClass.onPreExecute(MyBookDroidActivity.java:115) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at android.os.AsyncTask.execute(AsyncTask.java:391) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.mybookdroid.MyBookDroidActivity.executeSubmitClass(MyBookDroidActivity.java:101) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.mybookdroid.MyBookDroidActivity.access$0(MyBookDroidActivity.java:99) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.mybookdroid.MyBookDroidActivity$1.onAuthSucceed(MyBookDroidActivity.java:86) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.facebook.SessionEvents.onLoginSuccess(SessionEvents.java:78) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.nda.facebook.FacebookConnector$IDRequestListener.onComplete(FacebookConnector.java:141) 
12-13 21:58:41.523: E/AndroidRuntime(31961): at com.facebook.android.AsyncFacebookRunner$2.run(AsyncFacebookRunner.java:254) 
12-13 22:01:47.193: E/AndroidRuntime(32216): Uncaught handler: thread Thread-32 exiting due to uncaught exception 
12-13 22:01:47.203: E/AndroidRuntime(32216): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.os.Handler.<init>(Handler.java:121) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.app.Dialog.<init>(Dialog.java:105) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.app.AlertDialog.<init>(AlertDialog.java:63) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.app.ProgressDialog.<init>(ProgressDialog.java:80) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.app.ProgressDialog.<init>(ProgressDialog.java:76) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.mybookdroid.MyBookDroidActivity$SubmitClass.onPreExecute(MyBookDroidActivity.java:115) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at android.os.AsyncTask.execute(AsyncTask.java:391) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.mybookdroid.MyBookDroidActivity.executeSubmitClass(MyBookDroidActivity.java:101) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.mybookdroid.MyBookDroidActivity.access$0(MyBookDroidActivity.java:99) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.mybookdroid.MyBookDroidActivity$1.onAuthSucceed(MyBookDroidActivity.java:86) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.facebook.SessionEvents.onLoginSuccess(SessionEvents.java:78) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.nda.facebook.FacebookConnector$IDRequestListener.onComplete(FacebookConnector.java:141) 
12-13 22:01:47.203: E/AndroidRuntime(32216): at com.facebook.android.AsyncFacebookRunner$2.run(AsyncFacebookRunner.java:254) 

我嘗試執行Looper.prepare（），但在這種情況下應用程序凍結總是。我應該如何執行AsyncTask？謝謝。

Answer 1

您需要從UI線程執行AsyncTask。你可以這樣做：

private void executeSubmitClass() { 
    runOnUiThread(new Runnable() { 
     @Override 
     public void run() { 
      new SubmitClass().execute(); 
     } 
    }); 
} 

Answer 2

您必須在主（UI）線程上調用asyncTask.execute()。