如何执行 AsyncTask 以检查 Internet 连接

Question

我有以下代码，我想做的是以编程方式检查是否有互联网连接。
由于我收到 NetworkOnMainThreadException，因此被建议使用 AsyncTask。
我想在 hasActiveInternetConnection(Context context) 上执行网络操作，如果连接到网络则返回 true，否则返回 false。
如何使用 AsyncTask 执行此操作？

 public class NetworkUtil extends AsyncTask<String, Void, String>{
        Context context;

        public NetworkUtil(Context context){
            this.context = context;
         }

    private ProgressDialog dialog;

    @Override
    protected void onPreExecute() {

        super.onPreExecute();
    }

    @Override
    protected String doInBackground(String... arg0) {
        if (new CheckNetwork(context).isNetworkAvailable()) 
        {
             try {
                 HttpURLConnection urlc = (HttpURLConnection) (new URL("http://www.google.com").openConnection());
                 urlc.setRequestProperty("User-Agent", "Test");
                 urlc.setRequestProperty("Connection", "close");
                 urlc.setConnectTimeout(1500); 
                 urlc.connect();
                 boolean url= (urlc.getResponseCode() == 200);
                 String str = String.valueOf(url);
                 return str;
             } catch (IOException e) {

             }
         } 


            // your get/post related code..like HttpPost = new HttpPost(url);
         else {
            Toast.makeText(context, "no internet!", Toast.LENGTH_SHORT).show();
        }


        return null;
    }
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        if (dialog.isShowing()) {
            dialog.dismiss();
        }
    }
    }

Answer 1

使用此类检查互联网连接...

public class CheckNetwork {
private Context context;

public CheckNetwork(Context context) {
    this.context = context;
}

public boolean isNetworkAvailable() {
    ConnectivityManager connectivityManager = (ConnectivityManager) context
            .getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo activeNetworkInfo = connectivityManager
            .getActiveNetworkInfo();
    return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}

}

然后.....

将这个 ASynTask 用于 httppost。

public class NetworkUtil extends AsyncTask<String, Void, String> {

private ProgressDialog dialog;

@Override
protected void onPreExecute() {
    dialog = new ProgressDialog(YourActivity.this);
    dialog.setMessage("Loading...");
    dialog.setCancelable(false);
    dialog.show();
    super.onPreExecute();
}

@Override
protected String doInBackground(String... arg0) {
    if (new CheckNetwork(YourActivity.this).isNetworkAvailable()) {
        // your get/post related code..like HttpPost = new HttpPost(url);
    } else {
        // No Internet 
        // Toast.makeText(YourActivity.this, "no internet!", Toast.LENGTH_SHORT).show();
    }
    return null;
}
@Override
protected void onPostExecute(String result) {
    super.onPostExecute(result);
    if (dialog.isShowing()) {
        dialog.dismiss();
    }
}

Answer 2

There is no way to get an Internet connexion state, you will always have the network connection state.

但我找到了一个很好的答案here：您向 google.com 发送请求！ :) 如果你愿意，你也可以尝试通过 unix 命令 ping 到谷歌！！

这里的家伙正在使用一个线程，并稍等片刻等待答案，然后返回一个布尔值。你在处理程序中做你的员工。这是他的代码：

public static void isNetworkAvailable(final Handler handler, final int timeout) {
    // ask fo message '0' (not connected) or '1' (connected) on 'handler'
    // the answer must be send before before within the 'timeout' (in milliseconds)

    new Thread() {
        private boolean responded = false;   
        @Override
        public void run() { 
            // set 'responded' to TRUE if is able to connect with google mobile (responds fast) 
            new Thread() {      
                @Override
                public void run() {
                    HttpGet requestForTest = new HttpGet("http://m.google.com");
                    try {
                        new DefaultHttpClient().execute(requestForTest); // can last...
                        responded = true;
                    } 
                    catch (Exception e) {
                    }
                } 
            }.start();

            try {
                int waited = 0;
                while(!responded && (waited < timeout)) {
                    sleep(100);
                    if(!responded ) { 
                        waited += 100;
                    }
                }
            } 
            catch(InterruptedException e) {} // do nothing 
            finally { 
                if (!responded) { handler.sendEmptyMessage(0); } 
                else { handler.sendEmptyMessage(1); }
            }
        }
    }.start();
}

然后，我定义处理程序：

Handler h = new Handler() {
    @Override
    public void handleMessage(Message msg) {

        if (msg.what != 1) { // code if not connected

        } else { // code if connected

        }   
    }
};

...并启动测试：

isNetworkAvailable(h,2000); // get the answser within 2000 ms

Answer 3

您的AsyncTask 应如下所示：

 private class NetworkUtilTask extends AsyncTask<Void, Void, Boolean>{
    Context context;

    public NetworkUtilTask(Context context){
        this.context = context;
     }

     protected Boolean doInBackground(Void... params) {
         return hasActiveInternetConnection(this.context);
     }
     protected void onPostExecute(Boolean hasActiveConnection) {
         Log.d(LOG_TAG,"Success=" + hasActiveConnection);
     }
 }

然后你会像下面这样执行它：

NetworkUtilTask netTask = new NetworkUtilTask(context);
netTask.execute();