Android的HTTP请求的AsyncTask

Question

我想实现一个类，它将处理我的申请，所有的HTTP请求，这将是基本上是：

• 获取业务（GET）的列表;
• 执行登录（POST）;
• 更新位置（POST）。

所以，我将不得不从服务器（JSON）得到结果字符串，并将其传递给另一个方法来处理响应。

我现在有这样的方法：

public class Get extends AsyncTask<Void, Void, String> { 
    @Override 
    protected String doInBackground(Void... arg) { 
     String linha = ""; 
     String retorno = ""; 

     mDialog = ProgressDialog.show(mContext, "Aguarde", "Carregando...", true); 

     // Cria o cliente de conexão 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(mUrl); 

     try { 
      // Faz a solicitação HTTP 
      HttpResponse response = client.execute(get); 

      // Pega o status da solicitação 
      StatusLine statusLine = response.getStatusLine(); 
      int statusCode = statusLine.getStatusCode(); 

      if (statusCode == 200) { // Ok 
       // Pega o retorno 
       BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent())); 

       // Lê o buffer e coloca na variável 
       while ((linha = rd.readLine()) != null) { 
        retorno += linha; 
       } 
      } 
     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 

     return retorno; 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     mDialog.dismiss(); 
    } 
} 

    public JSONObject getJSON(String url) throws InterruptedException, ExecutionException { 
     // Determina a URL 
     setUrl(url); 

     // Executa o GET 
     Get g = new Get(); 

     // Retorna o jSON 
     return createJSONObj(g.get()); 
    } 

但g.get()返回一个空的响应。我该如何解决这个问题？

Answer 1

我想你没有完全理解的AsyncTask的工作方式。但我相信你希望重用代码来完成不同的任务;如果是这样，你可以创建一个抽象类，然后扩展它实现你创建的抽象方法。它应该做的事是这样的：

public abstract class JSONTask extends AsyncTask<String, Void, String> { 
    @Override 
    protected String doInBackground(String... arg) { 
     String linha = ""; 
     String retorno = ""; 
     String url = arg[0]; // Added this line 

     mDialog = ProgressDialog.show(mContext, "Aguarde", "Carregando...", true); 

     // Cria o cliente de conexão 
     HttpClient client = new DefaultHttpClient(); 
     HttpGet get = new HttpGet(mUrl); 

     try { 
      // Faz a solicitação HTTP 
      HttpResponse response = client.execute(get); 

      // Pega o status da solicitação 
      StatusLine statusLine = response.getStatusLine(); 
      int statusCode = statusLine.getStatusCode(); 

      if (statusCode == 200) { // Ok 
       // Pega o retorno 
       BufferedReader rd = new BufferedReader(new InputStreamReader(response.getEntity().getContent())); 

       // Lê o buffer e coloca na variável 
       while ((linha = rd.readLine()) != null) { 
        retorno += linha; 
       } 
      } 
     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } 

     return retorno; // This value will be returned to your onPostExecute(result) method 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     // Create here your JSONObject... 
     JSONObject json = createJSONObj(result); 
     customMethod(json); // And then use the json object inside this method 
     mDialog.dismiss(); 
    } 

    // You'll have to override this method on your other tasks that extend from this one and use your JSONObject as needed 
    public abstract customMethod(JSONObject json); 
} 

，然后在你的活动代码应该是这样的：

YourClassExtendingJSONTask task = new YourClassExtendingJSONTask(); 
task.execute(url); 

Answer 2

您没有执行任务。你只是在创造它。我认为你需要：

Get g = new Get(); 
g.execute(); 

但是你正在以错误的方式使用任务的生命周期。 OnPostExecute在主线程上运行，您应该根据需要执行所有更新。例如，您可以将任务传递给View。

Answer 3

看起来您从来没有真正通过调用Get对象的execute（）函数来启动AsyncTask。

试试这个代码：

Get g = new Get(); 
g.execute();