Unity3d中制作Loading场景进度条所遇到的问题

背景

通常游戏的主场景包含的资源较多，这会导致加载场景的时间较长。为了避免这个问题，可以首先加载Loading场景，然后再通过Loading场景来加载主场景。因为Loading场景包含的资源较少，所以加载速度快。在加载主场景的时候一般会在Loading界面中显示一个进度条来告知玩家当前加载的进度。在Unity中可以通过调用

Application.LoadLevelAsync

函数来异步加载游戏场景，通过查询

AsyncOperation.progress

的值来得到场景加载的进度。

尝试——遇到问题

第一步当加载完Loading场景后，调用如下的

LoadGame

函数开始加载游戏场景，使用异步加载的方式加载场景1(Loading场景为0，主场景为1)，通过Unity提供的Coroutine机制，我们可以方便的在每一帧结束后调用

SetLoadingPercentage

函数来更新界面中显示的进度条的数值。

<code class="csharp" style="word-wrap: break-word;"><span class="k" style="word-wrap: break-word;">public</span> <span class="k" style="word-wrap: break-word;">void</span> <span class="nf" style="word-wrap: break-word;">LoadGame</span><span class="p" style="word-wrap: break-word;">()</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">StartCoroutine</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">StartLoading_1</span><span class="p" style="word-wrap: break-word;">(</span><span class="m" style="word-wrap: break-word;">1</span><span class="p" style="word-wrap: break-word;">));</span>
<span class="p" style="word-wrap: break-word;">}</span>

<span class="k" style="word-wrap: break-word;">private</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">IEnumerator</span> <span class="nf" style="word-wrap: break-word;">StartLoading_1</span><span class="p" style="word-wrap: break-word;">(</span><span class="kt" style="word-wrap: break-word;">int</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">scene</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">AsyncOperation</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">Application</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">LoadLevelAsync</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">scene</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(!</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">isDone</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;">*</span> <span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="p" style="word-wrap: break-word;">}</span>
<span class="p" style="word-wrap: break-word;">}</span>
</code>

最后进度条的效果显示如下:



进度条并没有连续的显示加载的进度，而是停顿一下切换一个数字，再停顿一下切换一个数子，最后在没有显示100%就情况下就切换到主场景了。究其原因在于

Application.LoadLevelAsync

并不是真正的后台加载，它在每一帧加载一些游戏资源，并给出一个progress值，所以在加载的时候还是会造成游戏卡顿，

AsyncOperation.progress

的值也不够精确。当主场景加载完毕后Unity就自动切换场景，所以上述代码中的while循环体内的代码是不会被调用的，导致进度条不会显示100%。

修补——100%完成

为了让进度条能显示100%，取巧一点的办法是将

AsyncOperation.progress

的值乘上2，这样当加载到50%的时候界面上就显示100%了。缺点是当界面上显示100%的时候，用户还要等待一段时间才会进入游戏。其实Unity提供了手动切换场景的方法，把

AsyncOperation.allowSceneActivation

设为

false

就可以禁止Unity加载完毕后自动切换场景，修改后的

StartLoading_2

代码如下:

<code class="csharp" style="word-wrap: break-word;"><span class="c1" style="word-wrap: break-word;">// this function is not work</span>
<span class="k" style="word-wrap: break-word;">private</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">IEnumerator</span> <span class="nf" style="word-wrap: break-word;">StartLoading_2</span><span class="p" style="word-wrap: break-word;">(int scene)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">AsyncOperation</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">Application</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">LoadLevelAsync</span><span class="p" style="word-wrap: break-word;">(scene</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">false</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(!</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">isDone</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;">*</span> <span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="p" style="word-wrap: break-word;">}</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">true</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="p" style="word-wrap: break-word;">}</span>
</code>

我们首先将

AsyncOperation.allowSceneActivation

设为

false

，当加载完成后再设为

true

。代码看上去没有错，但是执行的结果是进度条最后会一直停留在90%上，场景不会切换。通过打印log发现

AsyncOperation.isDone

一直为

false

，

AsyncOperation.progress

的值增加到0.9后就保持不变了，也就是说场景永远不会被加载完毕。



在这个帖子中找到了答案，原来把

allowSceneActivation

设置为

false

后，Unity就只会加载场景到90%，剩下的10%要等到

allowSceneActivation

设置为

true

后才加载，这不得不说是一个坑。所以代码改为如下。当

AsyncOperation.progress

到达0.9后，就直接把进度条的数值更新为100%，然后设置

AsyncOperation.allowSceneActivation

为

ture

，让Unity继续加载未完成的场景。

<code class="csharp" style="word-wrap: break-word;"><span class="k" style="word-wrap: break-word;">private</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">IEnumerator</span> <span class="nf" style="word-wrap: break-word;">StartLoading_3</span><span class="p" style="word-wrap: break-word;">(int scene)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">AsyncOperation</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">Application</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">LoadLevelAsync</span><span class="p" style="word-wrap: break-word;">(scene</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">false</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;"><</span> <span class="m" style="word-wrap: break-word;">0.9f</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;">*</span> <span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="p" style="word-wrap: break-word;">}</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">true</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="p" style="word-wrap: break-word;">}</span>
</code>

最后的效果如下：

打磨——增加动画

上述的进度条虽然解决了100%显示的问题，但由于进度条的数值更新不是连续的，所以看上去不够自然和美观。为了看上去像是在连续加载，可以每一次更新进度条的时候插入过渡数值。这里我采用的策略是当获得

AsyncOperation.progress

的值后，不立即更新进度条的数值，而是每一帧在原有的数值上加1，这样就会产生数字不停滚动的动画效果了，迅雷中显示下载进度就用了这个方法。

<code class="csharp" style="word-wrap: break-word;"><span class="k" style="word-wrap: break-word;">private</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">IEnumerator</span> <span class="nf" style="word-wrap: break-word;">StartLoading_4</span><span class="p" style="word-wrap: break-word;">(int scene)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="kt" style="word-wrap: break-word;">int</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="m" style="word-wrap: break-word;">0</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="kt" style="word-wrap: break-word;">int</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">toProgress</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="m" style="word-wrap: break-word;">0</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">AsyncOperation</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">Application</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">LoadLevelAsync</span><span class="p" style="word-wrap: break-word;">(scene</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">false</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;"><</span> <span class="m" style="word-wrap: break-word;">0.9f</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">toProgress</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="p" style="word-wrap: break-word;">(</span><span class="kt" style="word-wrap: break-word;">int</span><span class="p" style="word-wrap: break-word;">)</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">progress</span> <span class="p" style="word-wrap: break-word;">*</span> <span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span> <span class="p" style="word-wrap: break-word;"><</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">toProgress</span><span class="p" style="word-wrap: break-word;">)</span> <span class="p" style="word-wrap: break-word;">{</span>
<span class="p" style="word-wrap: break-word;">++</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="p" style="word-wrap: break-word;">}</span>
<span class="p" style="word-wrap: break-word;">}</span>

<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">toProgress</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="m" style="word-wrap: break-word;">100</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="k" style="word-wrap: break-word;">while</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span> <span class="p" style="word-wrap: break-word;"><</span> <span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">toProgress</span><span class="p" style="word-wrap: break-word;">){</span>
<span class="p" style="word-wrap: break-word;">++</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">SetLoadingPercentage</span><span class="p" style="word-wrap: break-word;">(</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">displayProgress</span><span class="p" style="word-wrap: break-word;">);</span>
<span class="k" style="word-wrap: break-word;">yield</span> <span class="k" style="word-wrap: break-word;">return</span> <span class="k" style="word-wrap: break-word;">new</span> <span class="nf" style="word-wrap: break-word;">WaitForEndOfFrame</span><span class="p" style="word-wrap: break-word;">();</span>
<span class="p" style="word-wrap: break-word;">}</span>
<span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">op</span><span class="p" style="word-wrap: break-word;">.</span><span class="n" style="word-wrap: break-word; padding-top: 15px; border: none; background: none transparent !important;">allowSceneActivation</span> <span class="p" style="word-wrap: break-word;">=</span> <span class="k" style="word-wrap: break-word;">true</span><span class="p" style="word-wrap: break-word;">;</span>
<span class="p" style="word-wrap: break-word;">}</span>
</code>

displayProgress

用来记录要显示在进度条上的数值，最后进度条的动画如下：



对比第一种的进度条

总结

如果在加载游戏主场景之前还需要解析数据表格，生成对象池，进行网络连接等操作，那么可以给这些操作赋予一个权值，利用这些权值就可以计算加载的进度了。如果你的场景加载速度非常快，那么可以使用一个假的进度条，让玩家看上几秒钟的loading动画，然后再加载场景。总之进度条虽然小，但要做好也是不容易的。