Android中的“再按一次返回键退出程序”代码实现

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用户在退出应用前给出一个提示是很有必要的,因为可能是用户并不真的想退出,而只是一不小心按下了返回键,大部分应用也是这么做的,但也有些应用的做法是在应用退出去前给出一个Dialog,我觉得这样不太友好,用户还得移动手指去按dialog中的“确定”按钮。我觉得再按一次“返回”键退出程序是佳的用户体验,实现也很简单,代码如下:
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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;  
    }
    return super.onKeyDown(keyCode, event);
}
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<span style="white-space:pre">  </span>private long exitTime = 0;
<span style="white-space:pre">  </span>@Override
<span style="white-space:pre">  </span>public boolean onKeyDown(int keyCode, KeyEvent event) {
<span style="white-space:pre">      </span>// TODO Auto-generated method stub
<span style="white-space:pre">      </span>switch (keyCode) {
<span style="white-space:pre">      </span>case KeyEvent.KEYCODE_BACK:
<span style="white-space:pre">          </span>if((System.currentTimeMillis() - exitTime) > 2000){
<span style="white-space:pre">              </span>toast("再按一次返回键退出程序!");
<span style="white-space:pre">              </span>exitTime = System.currentTimeMillis();
<span style="white-space:pre">              </span>return false;
<span style="white-space:pre">          </span>}else{
<span style="white-space:pre">              </span>finish();
<span style="white-space:pre">              </span>System.exit(0);
<span style="white-space:pre">          </span>}
<span style="white-space:pre">          </span>break;
 
 
<span style="white-space:pre">      </span>default:
<span style="white-space:pre">          </span>break;
<span style="white-space:pre">      </span>}
<span style="white-space:pre">      </span>return super.onKeyDown(keyCode, event);
<span style="white-space:pre">  </span>}

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