当您单击返回时，应用程序会继续在后台运行.如果您想在退出某个活动时随时停止播放音乐，请覆盖 onStop 或 onPause 以停止您的声音.类似的东西

When you click back, the app keeps on running in the background. If you want to stop the music any time you get out of a certain activity override onStop or onPause to stop your sound. Something like that

@Override
protected void onStop(){
    super.onStop();
    //your code for stopping the sound
}