双击退出

  @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
    
    

        // 定义一个 long 类型变量用来存储 点击时长
        long time= 0;
        
        if(keyCode==KeyEvent.KEYCODE_BACK){
    
    

            if(System.currentTimeMillis()-time>2000){
    
    
                Toast.makeText(this, "双击退出", Toast.LENGTH_SHORT).show();
                time = System.currentTimeMillis();
                return  true;
            }else{
    
    
                finish();
            }

        }
        return super.onKeyDown(keyCode, event);
    }