IOS Programming UIWindow Switch

<span id="Label3"></p><p><p>As a result of the recent project needs to create a customizable bottom pop-up effect, so the study of uiactionsheet, intends to rewrite a custom pop-up window, when writing the demo for Lazy reasons, directly in the new project</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">-(<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2;">void</span>) Viewdidload {}</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">The window switch test code is written, and the result is the following error message when Debugging:</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><strong>Terminating app due to uncaught exception ' nsinternalinconsistencyexception ', reason: ' application windows is expected to has a root view controller at the end of application launch '</strong></p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">?</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: #3d1d81;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: #3d1d81;">Searched the internet for a while most of my friends said it was due to the version of Xcode and needed to be</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">-(<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2;">BOOL</span>) application: (<span style="font-variant-ligatures: no-common-ligatures; color: #703daa;">uiapplication</span> *) application didfinishlaunchingwithoptions: ( <span style="font-variant-ligatures: no-common-ligatures; color: #703daa;"> Nsdictionary</span> *) launchoptions {}</p></p><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;"><p style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;">?</p></p><p><p>method, Add a Rootviewcontroller manually. Follow the above method after the issue is still reported the same bug, then the window switch code written to the button click event, by clicking the event trigger Switch. This problem is solved by this method.</p></p><p><p>Preliminary cause Analysis:</p></p><p><p>May be in the <span style="font-family: Menlo; font-size: 11px; line-height: 13px;">viewdidload when the interface is not drawn, and at this time to switch the window so that caused the error of the exception, this is only one-sided speculation, I hope to have known friends to Correct. </span></p></p><p><p>IOS Programming UIWindow Switch</p></p></span>