1、默认的启动画面其实是那个3点钟的钟表图片，而我们需要在Package.appxmanifest文件中的Application UI模块里重新选择splash图片即可.
图片的大小得是 620*300，或者868 x 420 (1.4倍) ,1116 x 540(1.8倍)，支持PNG
当重新激活应用时启动画面也会显示.
2、如果想延时启动画面的显示时间，得在启动画面显示完成后自己添加模拟启动画面的页面，但是在两个画面衔接时会有闪烁。
这里有一段话教怎么避免这个难看的闪烁，但是我没有完全看懂，希望园子里看懂的朋友翻译一下
If you use fragment loading to load your imitation splash screen page, you may notice a flicker between when the Windows splash screen is dismissed and when your page is displayed. You see this flicker because fragment loading begins to load your imitation splash screen page asynchronously, before the activated event handler finishes executing. You can avoid this unsightly flicker entirely by avoiding the use of fragment loading in your imitation splash screen page. When your additional loading tasks are complete (as demonstrated by the Splash screen sample) you can then navigate to your app’s main page. Alternatively, if you wish to continue the use of fragment loading in your imitation splash screen page, you can also prevent the flicker by getting a deferral and responding to activated events asynchronously. Get a deferral for an activated event by calling the activatedOperation.getDeferral method.
注意：不要使用启动画面显示广告，也不要把启动画面当成about页面。