Android 两次按Back键退出应用(转)

    private long exitTime = 0; 
     
    @Override 
    public boolean onKeyDown(int keyCode, KeyEvent event) { 
        if(keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN){ 
                     
        if((System.currentTimeMillis()-exitTime) > 2000){ 
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();                              
            exitTime = System.currentTimeMillis(); 
        } 
        else{ 
            finish(); 
            System.exit(0); 
        } 
                     
            return true; //返回true表示执行结束不需继续执行父类按键响应
        } 
        return super.onKeyDown(keyCode, event); 
    }