Android 设备监听网络状态变化

Android 网络状态的变化监听目前主要有两种方式，一种是通过 ConnectivityManager 网络连接管理类来注册监听网络状态回调，另一种则是通过广播来实现。

1、通过 ConnectivityManager 来实现

1. 创建 ConnectivityManager 对象

ConnectivityManager connectivityManager = (ConnectivityManager) application.getSystemService(Context.CONNECTIVITY_SERVICE);

2. 添加注册回调方法
   在 Android SDK 版本 21- 26 之间，调用 ConnectivityManager 的 registerNetworkCallback 方法

/**
     * Registers to receive notifications about all networks which satisfy the given
     * {@link NetworkRequest}.  The callbacks will continue to be called until
     * either the application exits or {@link #unregisterNetworkCallback(NetworkCallback)} is
     * called.
     *
     * @param request {@link NetworkRequest} describing this request.
     * @param networkCallback The {@link NetworkCallback} that the system will call as suitable
     *                        networks change state.
     *                        The callback is invoked on the default internal Handler.
     */
    @RequiresPermission(android.Manifest.permission.ACCESS_NETWORK_STATE)
    public void registerNetworkCallback(@NonNull NetworkRequest request,
            @NonNull NetworkCallback networkCallback) {
        registerNetworkCallback(request, networkCallback, getDefaultHandler());
    }

其中包含2个参数
NetworkRequest：主要是用来定义一个网络请求，用于请求一个网络或者侦听请求改变

NetworkRequest.Builder builder = new NetworkRequest.Builder();
NetworkRequest request = builder.build();

NetworkCallback：用来回调网络变化信息

//定义一个类去继承 NetworkCallback，里面有很多方法可以实现，这里主要实现 onAvailable 当网络可以、onLost 当网络不可用
public class FTNetWorkCallback extends ConnectivityManager.NetworkCallback {

        @Override
        public void onAvailable(@NonNull Network network) {
            super.onAvailable(network);
            judgeNetState();
        }

        @Override
        public void onLost(@NonNull Network network) {
            super.onLost(network);
        }
    } 

最后传入参数即可

NetworkRequest.Builder builder = new NetworkRequest.Builder();
NetworkRequest request = builder.build();
connectivityManager.registerNetworkCallback(request, networkCallback);

在 Android 系统版本大于 26 时，直接传入回调类即可

connectivityManager.registerDefaultNetworkCallback(networkCallback);

2、通过广播来实现

因为在 Android 8.0 之后取消了很多静态广播，所以使用该方法要注意系统的版本。

IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
registerReceiver(networkReceiver, intentFilter); 

public class FTNetworkReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
            //添加判断网络状态的方法
        }
}

判断网络状态的方法见此链接