在MianActivity点击两次back退出app

代码如下

 private long exitTime = 0;//双击back退出间隔时间

  @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode == KeyEvent.KEYCODE_BACK){
            exit();
            return false;
        }
        return super.onKeyDown(keyCode, event);
    }

    //记录当前时间，若果两次点击间隔小于2s 退出
    private void exit(){
        if((System.currentTimeMillis() - exitTime)>2000){
            Toast.makeText(MainActivity.this,"再按一次退出拾贝",Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        }else{
            finish();
            //System.exit(0);
        }

    }