在AsyncTask中顯示Toast

Question

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

     public void onPreExecute(){ 


     } 
     @Override 
     protected String doInBackground(String... params) { 
      HttpClient client = new DefaultHttpClient(); 
      HttpGet get = new HttpGet(URL HERE); 
      try{ 
       HttpResponse responseGiven = client.execute(get); 
       StatusLine statusLine = responseGiven.getStatusLine(); 
       int statusCode = statusLine.getStatusCode(); 
       if(statusCode == 404){ 
        Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show(); 

       } 
      } catch(Exception e){ 

      } 
      return null; 
     } 

     public void onPostExecute(...){ 
      super.onPostExecute(s); 

     } 

    } 

但是，當我調試並運行應用程序時，它會得到Toast顯示。在AsyncTask工作的時候，有沒有辦法做到這一點？

謝謝！

Answer 1

你不能在doInBackground函數中顯示吐司，因爲在UI線程上doInBackground函數不起作用。您可以將進度發佈到onProgressUpdate函數。它將在UI線程上工作。

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

    private final Context context; 

    public ayncClass(Context context) { 
     this.context = context; 
    } 

    public void onPreExecute(){ 


    } 
    @Override 
    protected String doInBackground(String... params) { 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(URL HERE); 
     try{ 
      HttpResponse responseGiven = client.execute(get); 
      StatusLine statusLine = responseGiven.getStatusLine(); 
      int statusCode = statusLine.getStatusCode(); 
      if(stat-usCode == 404){ 
      // you can not use toast in doInBackground function. you need to pass to progress 
      publishProgress(0); 
      } 
     } catch(Exception e){ 

     } 
     return null; 
    } 

    @Override 
     protected void onProgressUpdate(Void... values) { 
     super.onProgressUpdate(values); 
     Toast.makeText(context, "ERROR", Toast.LENGTH_SHORT).show(); 
     } 

    public void onPostExecute(...){ 
     super.onPostExecute(s); 

    } 

} 

Answer 2

試試下面

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

    public void onPreExecute(){ 


    } 
    @Override 
    protected String doInBackground(String... params) { 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(URL HERE); 
     try{ 
      HttpResponse responseGiven = client.execute(get); 
      StatusLine statusLine = responseGiven.getStatusLine(); 
      int statusCode = statusLine.getStatusCode(); 
      if(statusCode == 404){ 
       // Toast.makeText(getApplicationContext(), "ERROR", //Toast.LENGTH_SHORT).show(); 

      } 
     } catch(Exception e){ 

     } 
     return String.valueOf(statusCode); // make this change 
    } 

    public void onPostExecute(String result){ 
     super.onPostExecute(s); 
Toast.makeText(getApplicationContext(), result, 
Toast.LENGTH_SHORT).show(); 
    } 

} 

Answer 3

你應該用我的代碼here：

public enum Toaster { 
    INSTANCE; 

    private final Handler handler = new Handler(Looper.getMainLooper()); 

    public void showToast(final Context context, final String message, final int length) { 
     handler.post(
      new Runnable() { 
       @Override 
       public void run() { 
        Toast.makeText(context, message, length).show(); 
       } 
      } 
     ); 
    } 

    public static Toaster get() { 
     return INSTANCE; 
    } 
} 

然後，你可以做

Toaster.get().showToast(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT); 

這將在用戶界面上運行代碼線程，它會工作。

Answer 4

Toast屬於UI。

我們只能在主線程（UI線程）中更新UI。

AsyncTask.doInBackground()將永遠不會在主線程中調用，這就是原因。

Answer 5

在PostExecute方法中始終放置Toast消息。

public void onPostExecute（...） { super.onPostExecute（s）;

Toast.makeText(context, "Hellooo I am at Post Execute method", Toast.LENGTH_SHORT).show(); 
    } 

Answer 6

Toast只能從UI線程顯示。在UI線程中調用onPostExecute，因此您可以將statusCode存儲在成員變量中，並在onPostExecute方法中檢查404，並在那裏顯示Toast。事情是這樣的：

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

    private int mStatusCode; 

    @Override 
    protected String doInBackground(String... params) { 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(URL HERE); 
     try{ 
      HttpResponse responseGiven = client.execute(get); 
      StatusLine statusLine = responseGiven.getStatusLine(); 
      mStatusCode = statusLine.getStatusCode(); 
     } catch(Exception e){ 
      // do NOT let catch blocks without log 
      // if something bad happens you will never know 
     } 
     return null; 
    } 

    public void onPostExecute(...){ 
     super.onPostExecute(s); 
     if(mStatusCode == 404){ 
      Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show(); 
     } 
    } 
} 

或者只是通過狀態代碼作爲參數傳遞給onPostExecute：

public class ayncClass extends AsyncTask<String, Void, Integer> { 

    @Override 
    protected Integer doInBackground(String... params) { 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(URL HERE); 
     try{ 
      HttpResponse responseGiven = client.execute(get); 
      StatusLine statusLine = responseGiven.getStatusLine(); 
      return statusLine.getStatusCode(); 
     } catch(Exception e){ 
      // do NOT let catch blocks without log 
      // if something bad happens you will never know 
     } 
     return -1; 
    } 

    public void onPostExecute(Integer statusCode){ 
     super.onPostExecute(s); 
     if(statusCode == 404){ 
      Toast.makeText(getApplicationContext(), "ERROR", Toast.LENGTH_SHORT).show(); 
     } 
    } 
} 

Answer 7

這可能有助於

onPreExecute（）{// 一些代碼＃1 }

doInBackground() { 
    runOnUiThread(new Runnable() { 
       public void run() { 
        // some code #3 (Write your code here to run in UI thread) 

       } 
      }); 
} 

onPostExecute() { 
    // some code #3 
} 

Answer 8

簡單，當你必須顯示的東西進入你的UI線程（例如吐司消息）然後寫：

runOnUiThread(new Runnable(){ 
    public void run() { 
     //Interaction with UI (Toast message) 
    } 
}); 

Answer 9

Toast是UI元素，它不來了，因爲你的應用程序的UI在UI線程上運行，而doInBackground方法的AsyncTask運行在不同的線程中。因此，無論您想要執行的與UI相關的操作應該在onPostExecute或onPreExecute之內。如果出現這種情況，您必須更新doInBackground中的用戶界面，您可以使用處理程序線程或最佳方式，您可以使用runOnUiThread方法，並在其中添加您的敬酒。