AysncTask - 從主UI調用線程

Question

我在AsyncTask期間嘗試顯示和隱藏對話框時遇到了問題我已將放在一起的活動放在我的Android應用程序中。

這是目前我在做什麼：

public void syncCard(final Tag tag) { 
    syncTask = new SyncTask(); 
    syncTask.execute(tag); 
} 

private class SyncTask extends AsyncTask<Tag, Void, Void> { 
    private final Dialog dialog; 
    private boolean mException; 

    public SyncTask() { 
     // Prepare dialog 
     dialog = buildSyncingDialog(); 
    } 

    @Override 
    protected void onPreExecute() { 
     dialog.show(); 
    } 

    @Override 
    protected Void doInBackground(Tag... params) { 
     mTagcomm = IsoDep.get(params[0]); 
     if (mTagcomm == null) { 
      //TODO - Handle communication error with the present card 
     } 
     mException = false; 

     try { 
      // Open connection 
      mTagcomm.connect(); 
      lastAts = getAts(mTagcomm); 

      mProvider.setmTagCom(mTagcomm); 

      EmvParser parser = new EmvParser(mProvider, true); 
      mCard = parser.readEmvCard(); 
      if (mCard != null) { 
       mCard.setAtrDescription(extractAtsDescription(lastAts)); 
      } 

     } catch (IOException e) { 
      mException = true; 
     } finally { 
      // close tagcomm 
      IOUtils.closeQuietly(mTagcomm); 
     } 

     return null; 
    } 

    @Override 
    protected void onPostExecute(Void result) { 
     if (dialog.isShowing()) { 
      dialog.dismiss(); 
     } 

     if (!mException) { 
      if (mCard != null) { 
       showPaymentCardDetails(); 
      } else if (mCard.isNfcLocked()) { 
       //TODO - Show error message informing user the card is locked 
      } 
     } else { 

     } 
    } 

    private Dialog buildSyncingDialog() { 
     String syncingText = String.format("%s\n%s", 
       getString(R.string.syncing), getString(R.string.do_not_remove_card)); 
     Dialog dialog = new CustomDialog(PaymentCardRegisterActivity.this, 
       syncingText, R.layout.layout_syncing); 
     dialog.setCancelable(false); 

     return dialog; 
    } 

    @Override 
    public void onCancelled() { 
     dialog.dismiss(); 
    } 
} 

我看到了以下錯誤：

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

我碰到這個老答案出來 - Can't create handler inside thread which has not called Looper.prepare()

但我對於我需要做什麼，m仍然有點困惑，對這篇文章的最後一個迴應是說從UI線程運行任務，我將如何使用上面的代碼去做這件事？

編輯

我的活動課，因爲我使用這個類來讀取非接觸式卡的詳細信息延伸NfcActivity。

我syncCard正在從另一個後臺線程（我相信）被稱爲像這樣

@Override 
public void onNewIntent(final Intent intent) { 
    super.onNewIntent(intent); 
    processIntent(intent); 
} 

private void processIntent(final Intent intent) { 
    String action = intent.getAction(); 

    if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) { 
     Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG); 
     onTagDiscovered(tagFromIntent); 
    } 
} 

@Override 
public void onTagDiscovered(final Tag tag) { 
    super.onTagDiscovered(tag); 
    try { 
     PaymentCardRegisterActivity.this.syncCard(tag); 
    } catch (Exception e) { 
     Log.e(PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e); 
     // Return to start activity 
     finish(); 
    } 
} 

Answer 1

如果onTagDiscovered是在一個線程，是不是UI線程中運行，那麼你應該派遣您的來電syncCard到主線程。如果您參考了Activity，則可以使用runOnUiThread併發布Runnable。這將確保Runnable在主線程上執行。 在你的代碼，我想你需要改變這種

@Override 
public void onTagDiscovered(final Tag tag) { 
    super.onTagDiscovered(tag); 
    try 
    { 
      PaymentCardRegisterActivity.this.syncCard(tag); 
    } 
    catch (Exception e) 
    { 
      Log.e(PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e); 
      // Return to start activity 
      finish(); 
    } 
} 

這個

@Override 
public void onTagDiscovered(final Tag tag) { 
    super.onTagDiscovered(tag); 
    runOnUiThread(new Runnable() { 

     public void run() { 
      try { 
       PaymentCardRegisterActivity.this.syncCard(tag); 
      } catch (Exception e) { 
       Log.e(PaymentCardRegisterActivity.class.getName(), "Failed to sync card", e); 
      } 
     } 
    }); 
}