Question

我想通过Web服务器接收和发送数据，但代码不起作用我该怎么做才能使这个代码工作？

请注意onCreate

中的此代码

try {

    URL url = new URL("http://myweb.com/");
    HttpURLConnection   connection = (HttpURLConnection) url.openConnection();
    InputStream Stream = connection.getInputStream();
    InputStreamReader reader = new InputStreamReader(Stream);
    BufferedReader b = new BufferedReader(reader);
    StringBuilder s = new StringBuilder();
    String str ="";

    while ((str = b.readLine())!=null)  {
        s.append(str);

    }
    String data = s.toString();
    TextView myText = (TextView) findViewById(R.id.Text);
    myText.setText(data);
} catch (MalformedURLException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

Answer 1

确保您在Android中的单独线程上执行与网络相关的任务。另外，请检查您是否设置了INTERNET权限。

如果您想从其他线程更新UI，则必须使用

runOnUiThread (new Runnable () {
    public void run() {
        //update ui in here
    }
}

Answer 2

所有代码都在主线程中运行，主线程应该始终用于设置UI和侦听UI事件，例如点击侦听器。

此线程不允许网络呼叫，因为它们可能需要很长时间。使用android的AsyncTask API，用于在单独的线程中运行代码。

为所有GET请求任务创建一个类如下所示的类。

public class DownloadTask extends AsyncTask<String, Void, Integer> {

    private String TAG = "InDownloadTask";
    private DownloadCallback callback;
    private String data;

    public DownloadTask(DownloadCallback cb){
        callback = cb;
    }

    @Override
    protected Integer doInBackground(String... params) {
        Integer result = 0;
        HttpURLConnection urlConnection;
        try {
            URL url = new URL(params[0]);
            urlConnection = (HttpURLConnection) url.openConnection();
            int statusCode = urlConnection.getResponseCode();

            if (statusCode == 200) {
                BufferedReader r = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
                StringBuilder response = new StringBuilder();
                String line;
                while ((line = r.readLine()) != null) {
                    response.append(line);
                }
                data = response.toString();
                result = 1;
            } else {
                result = 0;
            }
        } catch (Exception e) {
            Log.d(TAG, e.getLocalizedMessage());
        }
        return result;
    }

    @Override
    protected void onPostExecute(Integer integer) {
        super.onPostExecute(integer);
        callback.onFinishDownload(data, integer);
    }

}

创建一个我们用于上述类的回调接口。

public interface DownloadCallback {
    public void onFinishDownload(String data, Integer result);
}

现在来自你的活动onCreate

String url = "http://myweb.com/";
new DownloadTask(new DownloadCallback() {
    public void onFinishDownload(String data, Integer result) {
        if(result == 1)
            myText.setText(data);
        else 
            myText.setText("Error");
    }
}).execute(url);

如果您有许多与网络相关的操作，请使用Volley等网络库来处理此问题。

HttpURLConnection崩溃了应用程序

2 个答案: