当我改变我的api级别时，我的http请求不起作用

Question

当我的api级别设置为8时，一切都很好。但是当我尝试将minSdkVersion设置为11时，我获取xml的http请求不起作用。 if上有一个例外。 这是代码：

URL url;
    String ciao="";
    try {
      url = new URL("myurl");

      URLConnection connection = url.openConnection(); 

      HttpURLConnection httpConnection = (HttpURLConnection)connection; 
      int responseCode = httpConnection.getResponseCode(); 

      if (responseCode == HttpURLConnection.HTTP_OK) { 
        InputStream in = httpConnection.getInputStream(); 
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document dom = db.parse(in);
        DOMSource domSource = new DOMSource(dom);
        StringWriter writer = new StringWriter();
        StreamResult result = new StreamResult(writer);
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer = tf.newTransformer();
        transformer.transform(domSource, result);
        ciao=writer.toString();
      }
        }
    catch(Exception e)
    {

    }
    return ciao;

Answer 1

原因是，从API 11开始，您必须在后台线程上进行所有网络访问。如果不这样做，您将收到NetworkOnMainThreadException。这是为了防止用户界面在访问网络时无响应。

有关详细信息，请参阅here

Answer 2

确保您的清单有以下声明：

<uses-sdk android:minSdkVersion="number-of-version-you-want" />

然后

1. 清理项目
2. 重建项目。
3. 右键单击项目并选择运行，以便生成APK的更新版本。使用此APK。
4. 尝试在手机中卸载并重新安装该应用程序。

注意： 使用AsyncTask以避免主线程上出现ANR和NetworkOnMainThreadException异常。

修改 请找到你的asynctask代码：我还使用了progressDialog来显示＆＃34; loading请等待＆＃34;如果是一种消息，URL调用需要更长的时间。

public class MainActivity extends Activity
{   
@Override
protected void onCreate(Bundle savedInstanceState) 
{
    .... // Some code here
    // Async task can also be called from within an onclick code.
    new AsyncTaskOperation().execute("");
}


/* Async Task called to avoid Android Network On Main Thread Exception. Web services need to be consumed only in background.     */
private class AsyncTaskOperation extends AsyncTask <String, Void, Void>
{

    private ProgressDialog Dialog = new ProgressDialog(LoginActivity.this);
     String ciao="";
    protected void onPreExecute() {
        // Display the loading spinner
        Dialog.setMessage("Loading... Please wait.. ");
        Dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        Dialog.setInverseBackgroundForced(false);
        Dialog.setCancelable(false);
        Dialog.setIndeterminateDrawable(getResources().getDrawable(R.drawable.progressbar_new));

        Dialog.show();
    }

    @Override
    protected Void doInBackground(String... paramsObj) {
         try {
              url = new URL("myurl");

              URLConnection connection = url.openConnection(); 

              HttpURLConnection httpConnection = (HttpURLConnection)connection; 
              int responseCode = httpConnection.getResponseCode(); 

              if (responseCode == HttpURLConnection.HTTP_OK) { 
            InputStream in = httpConnection.getInputStream(); 
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            DocumentBuilder db = dbf.newDocumentBuilder();
            Document dom = db.parse(in);
            DOMSource domSource = new DOMSource(dom);
            StringWriter writer = new StringWriter();
            StreamResult result = new StreamResult(writer);
            TransformerFactory tf = TransformerFactory.newInstance();
            Transformer transformer = tf.newTransformer();
            transformer.transform(domSource, result);
            ciao=writer.toString();
              }
            }
            catch(Exception e)
            {

            }
        return null;
    }

    protected void onPostExecute(Void unused) 
    {
        // Close progress dialog
        Dialog.dismiss();
        // Do actions with ciao string

    } // End of method onPostExecute

} // End of class AsyncTaskOperation

} // MainActivity结束

Answer 3

API级别8允许从UI线程发出http请求。但是在更高版本中，在UI线程上发出http请求会抛出一个名为NetworkonMainThread异常的异常。要确认问题，请发布您的错误日志