1. 获取wifi信号强度

可以直接监听广播

MyReceiver receiver = new RssiReceiver();
IntentFilter intentFilter = new IntentFilter(WifiManager.RSSI_CHANGED_ACTION);
registerReceiver(receiver,intentFilter);

class MyReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        int rssi = intent.getIntExtra(WifiManager.EXTRA_NEW_RSSI,-1);
		//这函数可以计算出信号的等级
		int strength = WifiManager.calculateSignalLevel(rssi, 5);
    }
}

也可以从NetworkCallback中获取

@RequiresApi(api = Build.VERSION_CODES.N)
private void registerNetwork(){
    ConnectivityManager connMgr = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        connMgr.registerDefaultNetworkCallback(new ConnectivityManager.NetworkCallback(){
            @Override
            public void onAvailable(@NonNull Network network) {
                super.onAvailable(network);
                Log.d("NetworkCallback", "onAvailable: "+network);
            }

            @Override
            public void onLinkPropertiesChanged(@NonNull Network network, @NonNull LinkProperties linkProperties) {
                super.onLinkPropertiesChanged(network, linkProperties);
                Log.d("NetworkCallback", "onLinkPropertiesChanged: "+network);
            }

            @Override
            public void onCapabilitiesChanged(@NonNull Network network, @NonNull NetworkCapabilities networkCapabilities) {
                super.onCapabilitiesChanged(network, networkCapabilities);
                Log.d("NetworkCallback", "onCapabilitiesChanged: "+networkCapabilities.toString());
                if(networkCapabilities.hasCapability(NetworkCapabilities.NET_CAPABILITY_VALIDATED)){
					//判断是wifi还是移动网络
                    if(networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_WIFI)){
                        int strength = WifiManager.calculateSignalLevel(networkCapabilities.getSignalStrength(), 5);
                    }else {
                       
                    }
                }
            }

            @Override
            public void onLosing(@NonNull Network network, int maxMsToLive) {
                super.onLosing(network, maxMsToLive);
                Log.d("NetworkCallback", "onLosing: "+network);
            }

            @Override
            public void onLost(@NonNull Network network) {
                super.onLost(network);
                Log.d("NetworkCallback", "onLost: "+network);
            }

            @Override
            public void onUnavailable() {
                super.onUnavailable();
                Log.d("NetworkCallback", "onUnavailable: ");
            }
        });
    }
}

注意 networkCapabilities.getSignalStrength()在API29的时候才可以调用，低于29的时候为隐藏方法.可用反射调用。onCapabilitiesChanged这个函数在wifi强度变化时会调用，但是移动网络强度变化时确不会调用，而且在移动网络时getSignalStrength方法获取到的也不是信号强度。

2. 获取移动网络强度

可以直接监听PhoneStateListener，这里只是单卡的情况

private void phoneStateListener(){
    TelephonyManager mTelephonyManager = (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE);
    mTelephonyManager.listen(new PhoneStateListener(){

        @RequiresApi(api = Build.VERSION_CODES.M)
        @Override
        public void onSignalStrengthsChanged(SignalStrength signalStrength) {
            super.onSignalStrengthsChanged(signalStrength);
            int level = signalStrength.getLevel();
            Log.d("phoneStateListener", "onSignalStrengthsChanged: level "+level);
        }
        @Override
        public void onServiceStateChanged(ServiceState state) {
            Log.d("phoneStateListener", "onServiceStateChanged: "+state.toString());
        }

        @Override
        public void onDataConnectionStateChanged(int state, int networkType) {
            Log.d("phoneStateListener", "onDataConnectionStateChanged: state "+state+" networkType "+networkType);
        }
    }, PhoneStateListener.LISTEN_SIGNAL_STRENGTHS | PhoneStateListener.LISTEN_DATA_CONNECTION_STATE | PhoneStateListener.LISTEN_SERVICE_STATE);
}

如果是双卡的情况可以通过反射调用。但是我发现一个非常奇怪的现象，当打开相机时这里面的所有方法都会停止调用，原因不知道。没办法，只能取修改系统源码了，修改SystemUI的MobileSignalController.java

 @Override
 public void onSignalStrengthsChanged(SignalStrength signalStrength) {
     if (DEBUG) {
         Log.d(mTag, "onSignalStrengthsChanged signalStrength=" + signalStrength +
                 ((signalStrength == null) ? "" : (" level=" + signalStrength.getLevel())));
     }
     mSignalStrength = signalStrength;
     updateTelephony();
	//信号有强度有变化时发送广播	
	Intent intent = new Intent("android.net.mobile.RSSI_CHANGED");
	intent.putExtra("EXTRA_NEW_RSSI", signalStrength.getLevel());
	mContext.sendBroadcast(intent);
 }