Android中的“再按一次返回键退出程序”实现

long exitTime=0;

@Override
    public boolean onKeyDown(intkeyCode, 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;   
        }
        return super.onKeyDown(keyCode, event);
    }