android点击手机返回键触发事件

点击返回键，触发onKeyDown事件：

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
            checkExit();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }