AsyncTask的 - 都需要扩大和doInBackground什么参数？ [英] AsyncTask - what parameters are needed for extending and doInBackground?

问题描述

什么是不对的，它使用的AsyncTask code？尤其是： - 我需要把fetchSchools什么参数 - 我需要什么参数放在doInBackground？

What is wrong with this code that uses AsyncTask? In particular: - what parameters do I need to put in fetchSchools - what parameters do I need to put in doInBackground?

我发现很多有用的例子，但它们都使用伪code。在这些参数却没有解释什么，我确实需要放在那里。

I've found lots of "helpful" examples but they all use pseudocode in these parameters and don't explain what I actually need to put there.

我得到了Eclipse错误的方法fetchSchools必须实现继承的抽象方法AsynchTask ......

"I get the Eclipse error the method fetchSchools must implement the inherited abstract method AsynchTask..."

我并不需要通过这样的东西，我希望它返回一个字符串。

I don't need to pass this anything, I expect it to return a string.

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

public String doInBackground(String retval) {
       StringBuilder builder = new StringBuilder();
        HttpClient client = new DefaultHttpClient();

        HttpGet httpGet = new HttpGet("http://www.domain/schools.php");
        try 
     {
          HttpResponse response = client.execute(httpGet);
          StatusLine statusLine = response.getStatusLine();
          int statusCode = statusLine.getStatusCode();
          if (statusCode == 200) {
            HttpEntity entity = response.getEntity();
            InputStream content = entity.getContent();
            BufferedReader reader = new BufferedReader(new InputStreamReader(content));
            String
     line;

            int a=0;
            while ((line = reader.readLine()) != null) {
              builder.append(line);
            Log.i(MainActivity.class.getName(), "Reading in: " + a +" : "+ line);
            a++;
            }
          } else {
            Log.e(MainActivity.class.toString(), "Failed to download file");
          }
        } catch (ClientProtocolException e) {
          e.printStackTrace();
        } catch (IOException e)
     {
          e.printStackTrace();
        }

        return builder.toString(); 
}

protected void onPostExecute() {
}

}

推荐答案

你给doInBackground字符串参数，以便异步任务的第一个参数必须是字符串不为空。

you gave doInBackground a string parameter so async task first parameter must be string not void.

AsyncTask<String , Void, String> {

如果你不希望传递一个参数，不以doInBackground函数给出的参数。

If you don't want to pass a parameter, don't give parameter to doInBackground function.

浏览此网页AsyncTask的参考： <一href="http://developer.android.com/reference/android/os/AsyncTask.html">http://developer.android.com/reference/android/os/AsyncTask.html

check this page for asynctask reference: http://developer.android.com/reference/android/os/AsyncTask.html

的AsyncTask的第一个参数去doInBackground功能，第二个去onprogressUpdate功能，第三个参数尽皆onpostexecute功能。

First parameter of asynctask goes to doInBackground function, second one goes to onprogressUpdate function, third parameter foes to onpostexecute function.

我觉得要做到这一点：

 public class fetchSchools extends AsyncTask<Void, Void, String> {
    @Override
    protected String doInBackground(Void... arg0) {
      StringBuilder builder = new StringBuilder();
      HttpClient client = new DefaultHttpClient();
      // ...

     return builder.toString();
    }
    protected void onPostExecute(String retval) 
    {

    }
  }

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