网络状态改变、用户信息改变（帐户的钱），第一时间就要想到用观察者模式来实现

广播接收者，简单地把网络的变化通过接口抛出去

package com.qkt.face.et.receiver;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.util.Log;

import com.qkt.face.et.MyApplication;
import com.qkt.face.et.enums.NetworkType;
import com.qkt.face.et.utils.NetworkUtil;

import java.util.ArrayList;
import java.util.List;

public class NetStateChangeReceiver extends BroadcastReceiver {

    private static class InstanceHolder {
        private static final NetStateChangeReceiver INSTANCE = new NetStateChangeReceiver();
    }

    private List<NetStateChangeObserver> mObservers = new ArrayList<>();

    @Override
    public void onReceive(Context context, Intent intent) {

        if (ConnectivityManager.CONNECTIVITY_ACTION.equals(intent.getAction())) {
            NetworkType networkType = NetworkUtil.getNetworkType(context);
            Log.i("NetStateChangeReceiver", networkType.toString());
            notifyObservers(networkType);
        }
    }

    public static void registerReceiver(Context context) {
        IntentFilter intentFilter = new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
        context.registerReceiver(InstanceHolder.INSTANCE, intentFilter);
    }

    public static void unRegisterReceiver(Context context) {
        context.unregisterReceiver(InstanceHolder.INSTANCE);
    }

    public static void registerObserver(NetStateChangeObserver observer) {
        if (observer == null) {
            return;
        }
        if (!InstanceHolder.INSTANCE.mObservers.contains(observer)) {
            InstanceHolder.INSTANCE.mObservers.add(observer);
        }
    }

    public static void unRegisterObserver(NetStateChangeObserver observer) {
        if (observer == null) {
            return;
        }
        if (InstanceHolder.INSTANCE.mObservers == null) {
            return;
        }
        InstanceHolder.INSTANCE.mObservers.remove(observer);
    }

    private void notifyObservers(NetworkType networkType) {
        if (networkType == NetworkType.NETWORK_NO) {
            for (NetStateChangeObserver observer : mObservers) {
                observer.onNetDisconnected();
            }
        } else {
            for (NetStateChangeObserver observer : mObservers) {
                observer.onNetConnected(networkType);
            }
        }
    }
}

public enum  NetworkType {
    NETWORK_WIFI("WiFi"),
    NETWORK_4G("4G"),
    NETWORK_2G("2G"),
    NETWORK_3G("3G"),
    NETWORK_UNKNOWN("Unknown"),
    NETWORK_NO("No network");

    private String desc;
    NetworkType(String desc) {
        this.desc = desc;
    }

    @Override
    public String toString() {
        return desc;
    }
}

在需要的地方监听网络状态变化(记得销毁时删除监听器)，一般在BaseActivity

public class BaseActivity extends AppCompatActivity implements NetStateChangeObserver {
   
    @Override
    protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       NetStateChangeReceiver.registerObserver(this);
       registerReceiver();
    }
 
    @Override
    protected void onDestroy() {
        super.onDestroy();
        NetStateChangeReceiver.unRegisterObserver(this);
        unregisterReceiver();
    }
 
    @Override
    public void onNetDisconnected() {
        ivNet.setImageResource(R.drawable.netError);
    }

    //设置网络图标
    @Override
    public void onNetConnected(NetworkType networkType) {
        if (networkType.equals(NetworkType.NETWORK_WIFI) ) {
            getWifi();
        } else {
            ivNet.setImageResource(R.drawable.net_eth);
        }
    }
 
    //获取wifi信号强度
    private void getWifi() {
        //x心跳包请求成功，获取真实网速，请求失败，网络错误
        WifiManager wifi_service = (WifiManager) getContext().getApplicationContext().getSystemService(WIFI_SERVICE);
        WifiInfo wifiInfo = wifi_service.getConnectionInfo();

        int wStrength = Math.abs(wifiInfo.getRssi());
        if (wStrength < 50) {
            ivNet.setImageResource(R.drawable.net4);
        } else if (49 < wStrength && wStrength < 100) {
            ivNet.setImageResource(R.drawable.net3);
        } else if (100 < wStrength) {
            ivNet.setImageResource(R.drawable.net2);
        }

    }
 }

public class NetworkUtil {
    private NetworkUtil() {
        throw new UnsupportedOperationException("u can't instantiate me...");
    }

    @RequiresPermission("android.permission.ACCESS_NETWORK_STATE")
    private static NetworkInfo getActiveNetworkInfo(Context context) {
        ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        return cm.getActiveNetworkInfo();
    }

    /**
     * 获取当前网络类型
     * 需添加权限 {@code <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>}
     */
    @RequiresPermission("android.permission.ACCESS_NETWORK_STATE")
    public static NetworkType getNetworkType(Context context) {
        NetworkType netType = NetworkType.NETWORK_NO;
        NetworkInfo info = getActiveNetworkInfo(context);
        if (info != null && info.isAvailable()) {

            if (info.getType() == ConnectivityManager.TYPE_WIFI) {
                netType = NetworkType.NETWORK_WIFI;
            } else if (info.getType() == ConnectivityManager.TYPE_MOBILE) {
                switch (info.getSubtype()) {

                    case TelephonyManager.NETWORK_TYPE_TD_SCDMA:
                    case TelephonyManager.NETWORK_TYPE_EVDO_A:
                    case TelephonyManager.NETWORK_TYPE_UMTS:
                    case TelephonyManager.NETWORK_TYPE_EVDO_0:
                    case TelephonyManager.NETWORK_TYPE_HSDPA:
                    case TelephonyManager.NETWORK_TYPE_HSUPA:
                    case TelephonyManager.NETWORK_TYPE_HSPA:
                    case TelephonyManager.NETWORK_TYPE_EVDO_B:
                    case TelephonyManager.NETWORK_TYPE_EHRPD:
                    case TelephonyManager.NETWORK_TYPE_HSPAP:
                        netType = NetworkType.NETWORK_3G;
                        break;

                    case TelephonyManager.NETWORK_TYPE_LTE:
                    case TelephonyManager.NETWORK_TYPE_IWLAN:
                        netType = NetworkType.NETWORK_4G;
                        break;

                    case TelephonyManager.NETWORK_TYPE_GSM:
                    case TelephonyManager.NETWORK_TYPE_GPRS:
                    case TelephonyManager.NETWORK_TYPE_CDMA:
                    case TelephonyManager.NETWORK_TYPE_EDGE:
                    case TelephonyManager.NETWORK_TYPE_1xRTT:
                    case TelephonyManager.NETWORK_TYPE_IDEN:
                        netType = NetworkType.NETWORK_2G;
                        break;
                    default:
                        String subtypeName = info.getSubtypeName();
                        if (subtypeName.equalsIgnoreCase("TD-SCDMA")
                                || subtypeName.equalsIgnoreCase("WCDMA")
                                || subtypeName.equalsIgnoreCase("CDMA2000")) {
                            netType = NetworkType.NETWORK_3G;
                        } else {
                            netType = NetworkType.NETWORK_UNKNOWN;
                        }
                        break;
                }
            } else {
                netType = NetworkType.NETWORK_UNKNOWN;
            }
        }
        return netType;
    }
}