Question

我知道网络任务应该在异步线程中完成，我认为我的代码在一个内部，但我仍然得到错误

.MainActivity}：android.os.NetworkOnMainThreadException

让我感到困惑，因为几乎所有内容都在异步任务中：

    public void onStart() {
        super.onStart();
        new GetRssFeedTask().execute();
    }

其余代码在Async任务中：

  private class GetRssFeedTask extends AsyncTask<Void, Void, List<String>> {
        private String getRssFeed() throws IOException {
            InputStream in = null;
            String rssFeed = null;
            try {
                URL url = new URL("http://stuffilikenet.wordpress.com/feed/main.xml");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                in = conn.getInputStream();
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                byte[] buffer = new byte[1024];
                for (int count; (count = in.read(buffer)) != -1; ) {
                    out.write(buffer, 0, count);
                }
                byte[] response = out.toByteArray();
                rssFeed = new String(response, "UTF-8");
            } finally {
                if (in != null) {
                    in.close();
                }
            }
            return rssFeed;
        }      

  ...rest of code (seriously)...
  }

我应该在哪里查找错误？

Answer 1

网络任务应该在doInBackground（）中完成。

doInBackground（）回调方法在后台池中运行线程。要更新UI，您应该实现onPostExecute（），它从doInBackground（）传递结果并在UI中运行线程，这样您就可以安全地更新UI。

在onPreExecute（）方法中执行启动
在doInBackground（）方法中执行后台任务

更新onPostExecute（）方法中的UI

public class MyAyncTask extends AsyncTask<Void, Void, Void> {

@Override
protected void onPreExecute() {
    //Here you can show progress bar or something on the similar lines.
    //Since you are in a UI thread here.
    super.onPreExecute();
}

@Override
protected Void doInBackground(Void... params) {
    // Here you are in the worker thread and you are not allowed to access UI thread from here
    //Here you can perform network operations or any heavy operations you want.
    return null;
}

@Override
protected void onPostExecute(Void aVoid) {
    super.onPostExecute(aVoid);
    //After completing execution of given task , control will return here.
    //Hence if you want to populate UI elements with fetched data, do it here
}

@Override
protected void onProgressUpdate(Void... values) {
    super.onProgressUpdate(values);
    // You can track you progress update here
}

}

Answer 2

仅在AsyncTask课程中定义网络操作以在后台Thread上运行它们是不够的。

您必须在doInBackgrund()内执行它们。

您需要覆盖doInBackground()课程中的AsyncTask并在那里执行网络操作。

@Override
protected Void doInBackground(Void... params) {
    // here
    return null;
}

使用Async进行网络活动

2 个答案: