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[Android 開發] This message is already in use 解法

Oct 31st 2014, 11:16, by 張海芋

Handler 和 Message 是 Android 用來更新畫面的重要方法，有在開發 Android 的朋友都應該要知道這兩個的用法。而海芋最近使用這個方法來開發程式時，碰到了「android.util.AndroidRuntimeException: This message is already in use」這個問題，這是原本的寫法。

private int MSG_INCREASE_PROGRESSBAR = 9527;
private int MSG_Done = 5566;
private ProgressDialog m_progressDialog = null;
private Runnable m_runnable = new Runnable(){
 @Override
 public void run() 
 {
   try 
   {
      Message msg = new Message();
      for (int i = 0; i < 100; i++)
      {
        msg.what = MSG_INCREASE_PROGRESSBAR;
        m_Handler.sendMessage(msg);
      }
 
      msg.what = MSG_Done;
      m_Handler.sendMessage(msg);
    }catch (Exception e) {
      e.printStackTrace();
    }
 } 
};
 
private Handler m_Handler = new Handler()
{
 @Override
 public void handleMessage(Message msg) 
 {
     super.handleMessage(msg);
     switch (msg.what)
     {
       case MSG_INCREASE_PROGRESSBAR:
         if (m_progressDialog != null)
           m_progressDialog.incrementProgressBy(1);
         break;
       case MSG_DelteDone:
         if (m_progressDialog != null)
         {
           m_progressDialog.dismiss(); 
           m_progressDialog = null; 
         }
        break;
     } 
 } 
};

出現這個問題，海芋就去追查一下 Handler 這個 Class，原來在 Handler SendMessage 後，Handler 會將 Message 加入 MessageQueue 中，造成原本要處理的對象，已經不是原來的對象所致，所以要解決這個問題，必須在每次傳送 Message 給 Handler 前，先 New 一個 Message 元件，所以改成以下的寫法就可以囉！

private int MSG_INCREASE_PROGRESSBAR = 9527;
private int MSG_Done = 5566;
private ProgressDialog m_progressDialog = null;
private Runnable m_runnable = new Runnable(){
 @Override
 public void run() 
 {
     try 
     {
       for (int i = 0; i < 100; i++)
       {
         Message msg = new Message();
         msg.what = MSG_INCREASE_PROGRESSBAR;
         m_Handler.sendMessage(msg);
       }
      Message msg = new Message();
      msg.what = MSG_Done;
      m_Handler.sendMessage(msg);
    }catch (Exception e) {
      e.printStackTrace();
    }
 } 
};
 
private Handler m_Handler = new Handler()
{
 @Override
 public void handleMessage(Message msg) 
 {
    super.handleMessage(msg);
    switch (msg.what)
    {
      case MSG_INCREASE_PROGRESSBAR:
        if (m_progressDialog != null)
          m_progressDialog.incrementProgressBy(1);
        break;
      case MSG_DelteDone:
        if (m_progressDialog != null)
        {
           m_progressDialog.dismiss(); 
           m_progressDialog = null; 
         }
         break;
      }
 } 
};

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