// 模拟推送，在退出APP后的一段时间发送消息

    /**
     * 模仿推送，发消息
     */
    private void sendMessage() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(5000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                Intent intent = new Intent();
                intent.setAction("com.zx.lockscreenmsgdemo.LockScreenMsgReceiver");
                sendBroadcast(intent); //发送广播
            }
        }).start();
    }
}

/**
 * 监听锁屏消息的广播接收器
 */
public class LockScreenMsgReceiver extends BroadcastReceiver {
    private static final String TAG = "LockScreenMsgReceiver";

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.i(TAG, "onReceive:收到了锁屏消息 ");
        String action = intent.getAction();
        if (action.equals("com.zx.lockscreenmsgdemo.LockScreenMsgReceiver")) {
            //管理锁屏的一个服务
            KeyguardManager km = (KeyguardManager) context.getSystemService(Context.KEYGUARD_SERVICE);
            String text = km.inKeyguardRestrictedInputMode() ? "锁屏了" : "屏幕亮着的";
            Log.i(TAG, "text: " + text);
            if (km.inKeyguardRestrictedInputMode()) {
                Log.i(TAG, "onReceive:锁屏了 ");
                //判断是否锁屏
                Intent alarmIntent = new Intent(context, MessageActivity.class);
                //在广播中启动Activity的context可能不是Activity对象，所以需要添加NEW_TASK的标志，否则启动时可能会报错。
                alarmIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                context.startActivity(alarmIntent); //启动显示锁屏消息的activity
            }
        }
    }
}

public class MessageActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.i("tag", "onCreate:启动了消息内容的activity ");
        //四个标志位顾名思义，分别是锁屏状态下显示，解锁，保持屏幕长亮，打开屏幕。这样当Activity启动的时候，它会解锁并亮屏显示。
        Window win = getWindow();
        win.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED //锁屏状态下显示
                | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD //解锁
                | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON //保持屏幕长亮
                | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON); //打开屏幕
//        Drawable wallPaper = WallpaperManager.getInstance( this).getDrawable();
//        win.setBackgroundDrawable(wallPaper);
        setContentView(R.layout.activity_message);
    }
}

//先解锁系统自带锁屏服务，放在锁屏界面里面
KeyguardManager keyguardManager = (KeyguardManager) mContext.getSystemService(Context.KEYGUARD_SERVICE);
keyguardManager.newKeyguardLock("").disableKeyguard(); //解锁
//点击进入消息对应的页面
mContext.startActivity(new Intent(mContext, DetailsActivity.class));
finish();

<activity
            android:name=".activity.MessageActivity"
            android:excludeFromRecents="true"
            android:launchMode="singleInstance"
            android:taskAffinity="" />

  <!-- 解锁屏幕需要的权限 -->
    <uses-permission android:name="android.permission.DISABLE_KEYGUARD" />
    <!-- 申请电源锁需要的权限 -->
    <uses-permission android:name="android.permission.WAKE_LOCK" />