如何在Thread中運行Web服務代碼？

Question

我想通過此代碼從服務器獲取一些數據：

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;
    }
}

但是應用程序中存在一些延遲和暫停，因此我想在線程中運行此代碼，但是當我嘗試執行此代碼時，出現了一些錯誤，例如我無法返回結果或...

Answer 1

看看AsyncTask ：

網絡操作可能會涉及不可預測的延遲。 為防止這種情況導致不良的用戶體驗，請始終在與UI分開的線程上執行網絡操作。 AsyncTask類提供了從UI線程觸發新任務的最簡單方法之一。 有關此主題的更多討論，請參見博客文章“性能多線程”。

在以下代碼段中，myClickHandler（）方法調用新的DownloadWebpageTask（）。execute（stringUrl）。 DownloadWebpageTask類是AsyncTask的子類。

 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); } } ... }