AsyncTask在setOnClickListener中執行時無法正常工作

Question

我正在嘗試登錄到Web服務器，並且代碼正常運行，但是當我嘗試在頁面中創建日誌時，事情開始出錯。

我正在使用Eclipse Android工具提供的示例登錄頁面，如果有人想看到任何額外的代碼位。

如果我從OnClickHandler執行，那麼DefaultHttpClient似乎超時。它不返回任何東西，或者它返回「沒有同行證書」，我知道這是錯誤的。

/** 
* Keep track of the login task to ensure we can cancel it if requested. 
*/ 
private UserLoginTask mAuthTask = null; 

...設置的東西

mAuthTask = new UserLoginTask(); 
    findViewById(R.id.sign_in_button).setOnClickListener(
      new View.OnClickListener() { 
       @Override 
       public void onClick(View view) { 
        if(attemptLogin()){ 
         mAuthTask.execute(); 
        } 
       } 
      }); 
    //mAuthTask = new UserLoginTask(); 
    //mAuthTask.execute(); // Works if called from here. 

這裏的培訓相關的AsyncTask代碼：

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

    @Override 
    protected void onPreExecute() { 
     Log.i(TAG,"Thread name (from preexecute) : " + Thread.currentThread().getName()); 
    } 

    protected String doInBackground(String... urls) { 
     DefaultHttpClient client = AppHttpClient.getClient(); 
     HttpPost httppost = new HttpPost("https://euw.leagueoflegends.com/user/login"); 
     String result = ""; 
     try { 
      // Add your data 
      List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(3); 
      nameValuePairs.add(new BasicNameValuePair("name", "exampleusername")); 
      nameValuePairs.add(new BasicNameValuePair("pass", "blahblah")); 
      nameValuePairs.add(new BasicNameValuePair("form_id", "user_login")); 
      httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); 

      // Execute HTTP Post Request 
      Log.i(TAG,"Thread name (passed into doInBackground) : " + urls[0]); 
      Log.i(TAG,"Thread name (from doInBackground) : " + Thread.currentThread().getName()); 
      HttpResponse response2 = client.execute(httppost); 
      InputStream in = response2.getEntity().getContent(); 
      //result = readStream(in); 
     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 
     return result; 
    } 

    @Override 
    protected void onPostExecute(final String success) { 
     mAuthTask = null; 
     showProgress(false); 
    } 

    @Override 
    protected void onCancelled() { 
     mAuthTask = null; 
     showProgress(false); 
    } 
} 

Answer 1

下面是來自谷歌的工程師一個有趣的answer：

AsyncTask's pre and postExecute methods are invoked on the thread on which the task instance was created. Where you call execute() doesn't matter. The thread on which you create the task must be a looper thread and in practice should always be the main thread (or UI thread.)

編輯：

你應該試試這個代碼（未測試）：

private mAuthTask = new UserLoginTask(); 
findViewById(R.id.sign_in_button).setOnClickListener(
     new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       if(attemptLogin()){ 
        Activity.this.runOnUiThread(new Runnable() { 
         @Override 
         public void run() { 
          mAuthTask.execute(); 
         } 
        }); 
       } 
      } 
     });