如何实时观察网络变化

Answer 1

要实时观察连接变化，您可以使用 LiveData。在此之前我们使用了 BroadcastReceiver，但正如您所见 Declaring a broadcastreceiver for android.net.conn.CONNECTIVITY_CHANGE is deprecated for apps targeting N and higher.

我将发布完整的代码并解释它的每一部分。

public class ConnectionLiveData extends LiveData<Boolean> {
    private ConnectivityManager.NetworkCallback networkCallback;
    private final ConnectivityManager cm;
    private final HashSet<Network> validNetworks = new HashSet<>();
    private final ExecutorService executor = Executors.newSingleThreadExecutor();

    public static final int NETWORK_STATUS_POST_DELAY = 1000;

 public ConnectionLiveData(Context context) {
        cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    }

private void checkValidNetworks() {
    new Handler(Looper.getMainLooper()).postDelayed(() ->
                    postValue(validNetworks.size() > 0),
            NETWORK_STATUS_POST_DELAY);
}

@Override
protected void onActive() {
    networkCallback = createNetworkCallback();
    NetworkRequest networkRequest = new NetworkRequest.Builder()
            .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
            .build();
    cm.registerNetworkCallback(networkRequest, networkCallback);
}

@Override
protected void onInactive() {
    cm.unregisterNetworkCallback(networkCallback);
}

private ConnectivityManager.NetworkCallback createNetworkCallback() {
    return new ConnectivityManager.NetworkCallback() {
        /*
        Called when a network is detected. If that network has internet, save it in the Set.
        Source: https://developer.android.com/reference/android/net/ConnectivityManager.NetworkCallback#onAvailable(android.net.Network)
        */
        @Override
        public void onAvailable(@NonNull Network network) {
            NetworkCapabilities capabilities = cm.getNetworkCapabilities(network);
            boolean hasInternetCapability = capabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET);
            if (hasInternetCapability) {
                // check if this network actually has internet
                executor.execute(() -> {
                    boolean hasInternet = DoesNetworkHaveInternet.execute(network.getSocketFactory());
                    if (hasInternet) {
                        validNetworks.add(network);
                        checkValidNetworks();
                    }
                });
            }
        }

        /*
        If the callback was registered with registerNetworkCallback() it will be called for each network which no longer satisfies the criteria of the callback.
        Source: https://developer.android.com/reference/android/net/ConnectivityManager.NetworkCallback#onLost(android.net.Network)
        */
        @Override
        public void onLost(@NonNull Network network) {
            validNetworks.remove(network);
            checkValidNetworks();
        }
    };
}

}

我们在这里扩展LiveData 并实现两个功能：onActive() 和onInactive()。如您所知，LiveData 是生命周期感知的，当有一个观察者时，onActive 将被调用。我用它们来注册/注销ConnectivityManager。 当我们注册 ConnectivityManager 时，我们将 networkCallback 作为参数传递。它有几种方法，但正如您在 createNetworkCallback() 函数中看到的那样，我们仅覆盖 onAvailable() 和 onLost() 函数。如果您要打开/关闭网络，将调用 onAvailable() 和 onLost()。

可能存在连接打开但与服务器没有连接的情况。在这种情况下，我找到了一个简单的类，我们可以使用它来 ping 和验证我们的连接。 使用ExecutorService 我通过ping 验证互联网连接。

boolean hasInternet = DoesNetworkHaveInternet.execute(network.getSocketFactory());

DoesNetworkHaveInternet 代码：

public class DoesNetworkHaveInternet {

private static final String HOST_NAME = "8.8.8.8";
private static final int PORT = 53;
private static final int CONNECT_TIMEOUT = 1500;

@WorkerThread
static Boolean execute(SocketFactory socketFactory) {
    try {
        Socket socket = socketFactory.createSocket();
        socket.connect(new InetSocketAddress(HOST_NAME, PORT), CONNECT_TIMEOUT);
        socket.close();
        return true;
    } catch (IOException e) {
        e.printStackTrace();
        return false;
    }
}
}

它正在 ping 并验证我们有稳定的连接。 最后，在验证我们有连接之后，我们调用checkValidNetworks() 函数。有延迟，因为在某些情况下，您的连接可能会暂时关闭和打开，为此我发现没有必要显示网络错误。 checkValidNetworks() 检查validNetworks 是否不为空。这是一个列表，因为存在某些类型的连接，例如 wifi 和移动网络。如果至少有一个稳定的连接，validNetworks 不会为空。 而已。您可以在您的片段或这样的活动中观察它：

ConnectionLiveDataJava connectionLiveData = new ConnectionLiveDataJava(this);
connectionLiveData.observe(this, isConnected -> {
            
});