Android-让Activity不销毁，直接进入后台

重写Activity的onKeyUp()方法

@Override
public boolean onKeyUp(int keyCode, KeyEvent event)
{
    if(event.getAction() == KeyEvent.ACTION_UP){
        if(keyCode == KeyEvent.KEYCODE_BACK){
            moveTaskToBack(true);
            return true;
        }
    }
    return super.onKeyUp(keyCode, event);
}