一，蓝牙设备的连接，在广播注册之前连接：

1. 判断耳机的连接状态，我们比较常用的是广播的方式，但是在安卓8.0以后，如果耳机在注册广播之前连接，那么在注册广播，无法监听到耳机的状态，于是我们只能换一种方式去处理，代码如下：

AudioManager   mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
mAudioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
//获取当前使用的麦克风，设置媒体播放麦克风
if (mAudioManager.isWiredHeadsetOn()) {
	//todo 有线耳机已连接，声音内放，从耳机输出
}else{
	//todo 有线耳机未连接，声音外放，
}

2. 那么问题来了，如果连接了蓝牙设备呢，显然从广播的方式处理已经解决不了问题：

if (BluetoothProfile.STATE_CONNECTED == adapter.getProfileConnectionState(BluetoothProfile.HEADSET)) {
	//todo 蓝牙设备已连接，声音内放，从蓝牙设备输出
} else if (BluetoothProfile.STATE_DISCONNECTED == adapter.getProfileConnectionState(BluetoothProfile.HEADSET)) {
	//todo 蓝牙设备未连接，声音外放，
} else {
	//todo 蓝牙设备未连接，声音外放，
}

二，广播注册之后，耳机的连接状态发生改变，通过广播监听即可：

广播代码：

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothHeadset;
import android.bluetooth.BluetoothProfile;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Build;

import tv.buka.roomSdk.util.LogUtil;


/**
 * 耳机状态监听
 * <p>
 * Created by hwk on 2017/11/2.
 */
public class HeadsetPlugReceiver extends BroadcastReceiver {
    private static final String TAG = "HeadsetPlugReceiver";

    private HeadsetPlugListener mHeadsetPlugListener;

    public HeadsetPlugReceiver(HeadsetPlugListener headsetPlugListener) {
        this.mHeadsetPlugListener = headsetPlugListener;
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED.equals(action)) {
            LogUtil.e(TAG, action);
            BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
                int state = adapter.getProfileConnectionState(BluetoothProfile.HEADSET);
                if (BluetoothProfile.STATE_CONNECTED == state) {
                    mHeadsetPlugListener.onHeadsetPlug(true);
                }
                if (BluetoothProfile.STATE_DISCONNECTED== state) {
                    mHeadsetPlugListener.onHeadsetPlug(false);
                }
            }
        } else if (Intent.ACTION_HEADSET_PLUG.equals(action)) {
            if (intent.hasExtra("state")) {
                if (intent.getIntExtra("state", 0) == 0) {
                    //外放
                    mHeadsetPlugListener.onHeadsetPlug(true);
                } else if (intent.getIntExtra("state", 0) == 1) {
                    //耳机
                    mHeadsetPlugListener.onHeadsetPlug(false);
                }
            }
        }
    }

    public interface HeadsetPlugListener {
        void onHeadsetPlug(boolean isPlug);//true说明没有耳机   false说明有耳机
    }
}

实现代码：

//耳机植入监听
mHeadsetPlugReceiver = new HeadsetPlugReceiver(new HeadsetPlugReceiver.HeadsetPlugListener() {
	@Override
	public void onHeadsetPlug(boolean isPlug) {
		if (isPlug) {
			if (BluetoothProfile.STATE_CONNECTED == adapter.getProfileConnectionState(BluetoothProfile.HEADSET)) {
				//蓝牙设备输出
			} else if (BluetoothProfile.STATE_DISCONNECTED == adapter.getProfileConnectionState(BluetoothProfile.HEADSET)) {
				//外放
			} else {
				//外放
			}
		} else {
			//外放
		}
	}
});
IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(Intent.ACTION_HEADSET_PLUG);
intentFilter.addAction(BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED);
registerReceiver(mHeadsetPlugReceiver, intentFilter);

三，声音内放、和外放的处理

//外放
public void loudSpeaker(Activity context) {
	AudioManager audioManager = (AudioManager)context.getSystemService("audio");
	audioManager.setSpeakerphoneOn(true);
	context.setVolumeControlStream(0);
	audioManager.setMode(0);
}

//内放
public void microSpeaker(Activity context) {
	AudioManager audioManager = (AudioManager)context.getSystemService("audio");
	audioManager.setSpeakerphoneOn(false);
	context.setVolumeControlStream(0);
	audioManager.setMode(0);
}

总结：研究微信、qq开启视频通话的时候，有线耳机、蓝牙耳机的连接与断开，发现如果同时连接，声音从最后发生改变的那个设备输出。