第一次点击给了我一个错误的输出

Question

我已经修改了我之前的代码——这段代码运行正常。唯一的问题是，启动它后，第一次点击它总是显示输出为：

“互联网不可用”

但在第二次单击时，它会显示正确的输出。

public class MainActivity extends Activity {  

    boolean pingCheck;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button b1=(Button)findViewById(R.id.button1);

        b1.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {                   
                Thread t = new Thread(new Runnable() {
                    public void run() {
                        pingCheck = isURLReachable(getApplicationContext());
                    }
                });

                t.start();

                if(pingCheck)
                {
                    Toast.makeText(MainActivity.this,"Network is available",Toast.LENGTH_LONG).show();
                }
                else
                {
                    Toast.makeText(MainActivity.this,"Network not available",Toast.LENGTH_LONG).show();
                }                   
            }
        });
    }


    static public boolean isURLReachable(Context context) {
        ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo netInfo = cm.getActiveNetworkInfo();

        if (netInfo != null && netInfo.isConnected()) {
            try {
                URL url = new URL("http://google.com");   // Change to "http://google.com" for www  test.
                HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
                urlc.setConnectTimeout( 1000);          // 10 s.
                urlc.connect();

                if (urlc.getResponseCode() == 200) {        // 200 = "OK" code (http connection is fine).
                    Log.wtf("Connection", "Success !");
                    return true;
                } else {
                    return false;
                }
            } catch (MalformedURLException e1) {
                return false;
            } catch (IOException e) {
                return false;
            }
        }

        return false;
    }
}

Answer 1

您不能在线程中运行异步任务并在此之后立即检查结果。您需要等待任务完成。我建议您将回调传递给您的 ping 检查，一旦回调返回，请按照 if(pingCheck) 运行您的代码。

这应该可以完成工作：

public static interface OnInternetCheckCallback {
    void onInternetCheckResult(boolean available);
}

public static void hasInternetAccess(OnInternetCheckCallback callback) {
    new AsyncTask<OnInternetCheckCallback, Void, Boolean>() {
        private OnInternetCheckCallback mCallback;

        @Override
        protected Boolean doInBackground(OnInternetCheckCallback... params) {
            mCallback = params[0];
            try {
                URL checkUrl = new URL(HEALTHCHECK_URL);
                HttpURLConnection connection = (HttpURLConnection) checkUrl.openConnection();
                connection.setRequestProperty("User-Agent", "Android");
                connection.setRequestProperty("Connection", "close");
                connection.setConnectTimeout(1500);
                connection.connect();
                return (connection.getResponseCode() == 200 && connection.getContentLength() <= 0);
            } catch (IOException e) {
                Log.e(TAG, ".doInBackground() - Error checking internet connection", e);
            }
            return false;
        }

        @Override
        protected void onPostExecute(Boolean result) {
            mCallback.onInternetCheckResult(result);
        }
    }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, callback);
}

另外，可能更好的办法是检查您自己的服务器而不是 google.com，因为 Google 服务器在某些国家/地区被阻止。