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2023-06-02 07:00:05

如何检查Android上的互联网接入?InetAddress从不超时

我得到了一个AsyncTask，应该检查对主机名的网络访问。但是doInBackground()永远不会超时。有人知道吗?

public class HostAvailabilityTask extends AsyncTask<String, Void, Boolean> {

    private Main main;

    public HostAvailabilityTask(Main main) {
        this.main = main;
    }

    protected Boolean doInBackground(String... params) {
        Main.Log("doInBackground() isHostAvailable():"+params[0]);

        try {
            return InetAddress.getByName(params[0]).isReachable(30); 
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;       
    }

    protected void onPostExecute(Boolean... result) {
        Main.Log("onPostExecute()");

        if(result[0] == false) {
            main.setContentView(R.layout.splash);
            return;
        }

        main.continueAfterHostCheck();
    }   
}

当前回答

这是最简单和简单的方法来检查互联网连接的wifi和移动数据。

public static boolean isConnected(Activity _context) {
        if (_context != null) {
            ConnectivityManager connMgr = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo activeInfo = connMgr.getActiveNetworkInfo();
            if (activeInfo != null && activeInfo.isConnected()) {
                boolean wifiConnected = activeInfo.getType() == ConnectivityManager.TYPE_WIFI;
                boolean mobileConnected = activeInfo.getType() == ConnectivityManager.TYPE_MOBILE;

                if (wifiConnected || mobileConnected) {
                    Log.d(TAG, "Wifi Connected ");
                    return true;
                } else {
                    showAlert(_context,_context.getString(R.string.err_no_internet));
                    return false;
                }
            } else {
                showAlert(_context,_context.getString(R.string.err_no_internet));
                return false;
            }
        } else {
            Log.e(TAG, "networkConnectivity: Context NULL");

        }
        return false;
    }
2018-03-26 12:14:02

其他回答

我在这里看到了很多过时的答案，所以我决定加入我的答案。

由于Android 10 (API级别29)getActiveNetworkInfo()已弃用，谷歌建议我们使用NetworkCallbacks而不是针对Android 10及更高版本的应用程序。

关于阅读网络状态的文档提供了一些关于如何使用NetworkCallback的信息，但我没有设法找到一个很好的代码示例，整个事情的工作，所以这里是我提出的代码，我们在我们的应用程序中使用:

import android.content.Context
import android.net.ConnectivityManager
import android.net.LinkProperties
import android.net.Network
import android.net.NetworkCapabilities
import com.fieldontrack.kmm.common.network.ConnectivityMonitor
import com.fieldontrack.kmm.entities.connectivity.NetworkType
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow

class ConnectivityMonitorImpl(appContext: Context) : ConnectivityMonitor {
    private val connectivityManager = appContext.getSystemService(ConnectivityManager::class.java)
    private val networkCallback = object : ConnectivityManager.NetworkCallback() {
        override fun onAvailable(network: Network) =
            connectivityManager.getNetworkCapabilities(network)?.let { networkCapabilities ->
                updateConnectionStatus(networkCapabilities = networkCapabilities)
                updateNetworkType(networkCapabilities = networkCapabilities)
            } ?: run {
                _isConnectedState.value = true
            }

        override fun onLost(network: Network) {
            // Do not check for NetworkCapabilities here, as they might be wrong.
            // If we get this callback, we're certain that we've lost connection.
            _isConnectedState.value = false
            _networkTypeState.value = NetworkType.Unknown
        }

        override fun onCapabilitiesChanged(
            network: Network,
            networkCapabilities: NetworkCapabilities
        ) {
            updateConnectionStatus(networkCapabilities = networkCapabilities)
            updateNetworkType(networkCapabilities = networkCapabilities)
        }

        override fun onLinkPropertiesChanged(
            network: Network,
            linkProperties: LinkProperties
        ) = Unit
    }
    private val _isConnectedState = MutableStateFlow(false)
    private val _networkTypeState = MutableStateFlow(NetworkType.Unknown)

    override val isConnectedState: StateFlow<Boolean> = _isConnectedState
    override val networkTypeState: StateFlow<NetworkType> = _networkTypeState

    override val isConnected: Boolean
        get() = _isConnectedState.value

    override val networkType: NetworkType
        get() = _networkTypeState.value

    init {
        startMonitoring()
    }

    override fun startMonitoring() =
        connectivityManager.registerDefaultNetworkCallback(networkCallback)

    override fun stopMonitoring() =
        connectivityManager.unregisterNetworkCallback(networkCallback)

    private fun updateConnectionStatus(networkCapabilities: NetworkCapabilities) {
        val isConnected =
            networkCapabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)

        _isConnectedState.value = isConnected
    }

    private fun updateNetworkType(networkCapabilities: NetworkCapabilities) {
        val networkType = when {
            networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI) -> NetworkType.WiFi
            networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_CELLULAR) -> NetworkType.Cellular
            else -> NetworkType.Unknown
        }

        _networkTypeState.value = networkType
    }
}

ConnectivityMonitor界面非常简单:

interface ConnectivityMonitor {
    val isConnected: Boolean
    val networkType: NetworkType

    val isConnectedState: StateFlow<Boolean>
    val networkTypeState: StateFlow<NetworkType>
    
    fun startMonitoring()
    fun stopMonitoring()
}

NetworkType只是一个简单的枚举:

enum class NetworkType { Unknown, Cellular, WiFi }

据我测试，无论应用程序是在后台还是前台，这都是可行的。

2022-12-19 16:24:02

如果您想在连接丢失时显示警报。你可以使用下面的方法。

此方法用于一次检查连接。首先，你必须在你的类中创建这个。

private boolean isNetworkConnected() {
        ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        if(!(cm.getActiveNetworkInfo() != null && cm.getActiveNetworkInfo().isConnected())){
            showNetworkDialog();
            return false;
        }
        return true;
    }

在类中创建此方法作为连接侦听器。

private void ConnectionCheck(){
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkRequest networkRequest = new NetworkRequest.Builder().build();
            connectivityManager.registerNetworkCallback(networkRequest, new ConnectivityManager.NetworkCallback() {
                @Override
                public void onAvailable(Network network) {
                    super.onAvailable(network);
                    Log.i("Tag", "active connection");
                }

                @Override
                public void onLost(Network network) {
                    super.onLost(network);
                    Log.i("Tag", "losing active connection");
                    isNetworkConnected();
                }
            });
        }
    }

为了显示对话框，你可以创建showDialog()方法。

private void showNetworkDialog(){
    new AlertDialog.Builder(MainActivity.this)
            .setIcon(android.R.drawable.ic_dialog_alert)
            .setTitle("Connection lost?")
            .setMessage("Please check your internet connection!")
            .setCancelable(false)
            .setPositiveButton("Exit", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    finish();
                }
            })
            .setNegativeButton("Retry", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    isNetworkConnected();
                }
            })
            .show();
}

最后你可以在onCreate()方法中调用这个方法。

if(isNetworkConnected()){
            ConnectionCheck();
        }

在清单文件中，你必须提到许可。

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
2021-03-07 13:45:17

如果设备处于飞行模式(或者假设在没有可用网络的其他情况下)，cm.getActiveNetworkInfo()将为空，因此您需要添加一个空检查。

修改(Eddie的解决方案)如下:

public boolean isOnline() {
    ConnectivityManager cm =
        (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    return netInfo != null && netInfo.isConnectedOrConnecting();
}

在AndroidManifest.xml中添加以下权限:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

还有一点，如果你在给定的时间点绝对需要一个网络连接，那么使用netInfo.isConnected()而不是netInfo.isConnectedOrConnecting可能会更好。不过，我想这取决于个人用例。

2010-10-24 16:28:54

这个线程中的大多数答案只检查是否有可用的连接，但不检查该连接是否工作，其他答案不是设备范围，我的解决方案应该在每个设备上工作。

你可以在启动应用程序之前在你的主要活动中删除我的代码，它会快速确定是否有实际的互联网连接，如果有对话框将立即删除，应用程序将被启动，如果没有警报会弹出说应用程序需要互联网连接才能工作。

final AlertDialog alertDialog = new AlertDialog.Builder(this).create();
        alertDialog.setTitle("Checking Connection");
        alertDialog.setMessage("Checking...");
        alertDialog.show();
        new CountDownTimer(5000, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {

                new Thread(new Runnable() {
                    public void run() {
                        try {
                            URL url = new URL("http://web.mit.edu/");
                            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                            connection.setRequestMethod("GET");
                            connection.setConnectTimeout(5000);
                            isConnected = connection.getResponseCode() == HttpURLConnection.HTTP_OK;
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                }).start();

                if (isConnected == false){
                    alertDialog.setMessage("Try " +  (5 - millisUntilFinished/1000) + " of 5.");
                } else {
                    alertDialog.dismiss();
                }
            }
            @Override
            public void onFinish() {
                if (isConnected == false) {
                    alertDialog.dismiss();
                    new AlertDialog.Builder(activity)
                            .setTitle("No Internet")
                            .setMessage("Please connect to Internet first.")
                            .setPositiveButton(android.R.string.yes, new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int which) {
                                    // kill the app?
                                }
                            })
                            .setIcon(android.R.drawable.ic_dialog_alert)
                            .show();
                } else {
                    // Launch the app
                }
            }
        }.start();
2016-08-02 09:14:28

The other answers that use ConnectivityManager are wrong because having a network connection doesn't mean you have internet access. For example, the user might be connected to a coffee shop's WiFi portal but can't get to the internet. To check that the internet is accessible you have to try to connect to an actual server. Normally when you want to do this you have a specific server in mind that you want to connect to, so go ahead and check if you can connect to that server. Here's a simple method for checking connectivity to a server.

private boolean isOnTheInternet() {
    try {
        URLConnection urlConnection = new URL("http://yourserver").openConnection();
        urlConnection.setConnectTimeout(400);
        urlConnection.connect();
        return true;
    } catch (Exception e) {
        return false;
    }
}

设置ConnectTimeout的原因是，否则它默认为TCP超时，可以有很多秒长。

还要注意的是，Android不允许你在主线程上运行这个程序。

2014-01-31 02:55:27

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