Question

我想用这段代码从服务器获取一些数据：

public class Webservice {

    public static String readUrl(String url, ArrayList<NameValuePair> params) {
        try {
            HttpClient client = new DefaultHttpClient();
            HttpPost method = new HttpPost(url);

            if (params != null) {
                method.setEntity(new UrlEncodedFormEntity(params));
            }

            HttpResponse response = client.execute(method);

            InputStream inputStream = response.getEntity().getContent();
            String result = convertInputStreamToString(inputStream);

            return result;
        }
        catch (ClientProtocolException e) {
            e.printStackTrace();
        }
        catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }


    private static String convertInputStreamToString(InputStream inputStream) {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            StringBuilder builder = new StringBuilder();

            String line = "";

            while ((line = reader.readLine()) != null) {
                builder.append(line);
            }

            return builder.toString();
        }
        catch (IOException e) {
            e.printStackTrace();
        }

        return null;
    }
}

但是在应用程序中有一些延迟和暂停，所以我想在线程中运行此代码，但是当我尝试这样做时，我遇到了一些错误，例如我无法返回结果或。 ..

Answer 1

看看AsyncTask：

网络运营可能涉及不可预测的延迟。为了防止这种情况从导致糟糕的用户体验，始终执行网络操作在与UI的单独线程上。 AsyncTask类提供了一个从UI线程启动新任务的最简单方法。更多讨论这个主题，请参阅博客文章Multithreading For 性能

在以下代码段中，myClickHandler（）方法调用new DownloadWebpageTask（）。执行（stringUrl）。 DownloadWebpageTask class是AsyncTask的子类。

public class HttpExampleActivity extends Activity {
private static final String DEBUG_TAG = "HttpExample";
private EditText urlText;
private TextView textView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);   
    urlText = (EditText) findViewById(R.id.myUrl);
    textView = (TextView) findViewById(R.id.myText);
}

// When user clicks button, calls AsyncTask.
// Before attempting to fetch the URL, makes sure that there is a network connection.
public void myClickHandler(View view) {
    // Gets the URL from the UI's text field.
    String stringUrl = urlText.getText().toString();
    ConnectivityManager connMgr = (ConnectivityManager) 
        getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
    if (networkInfo != null && networkInfo.isConnected()) {
        new DownloadWebpageTask().execute(stringUrl);
    } else {
        textView.setText("No network connection available.");
    }
}

 // Uses AsyncTask to create a task away from the main UI thread. This task takes a 
 // URL string and uses it to create an HttpUrlConnection. Once the connection
 // has been established, the AsyncTask downloads the contents of the webpage as
 // an InputStream. Finally, the InputStream is converted into a string, which is
 // displayed in the UI by the AsyncTask's onPostExecute method.
 private class DownloadWebpageTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {

        // params comes from the execute() call: params[0] is the url.
        try {
            return downloadUrl(urls[0]);
        } catch (IOException e) {
            return "Unable to retrieve web page. URL may be invalid.";
        }
    }
    // onPostExecute displays the results of the AsyncTask.
    @Override
    protected void onPostExecute(String result) {
        textView.setText(result);
   }
}
... }

如何在Thread中运行Webservice代码？

1 个答案: