预览变为空白;有时在预览窗口中，有时在设计选项卡中，有时预览会出现，但视图无法点击。
我尝试从设计选项卡刷新布局，选择设计表面;但它有时只会有所帮助。 The preview goes blank as can be seen in the screenshot.
有关其他信息，我使用约束布局objc[6529]: Class VCWeakObjectHolder is implemented in both /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AVConference.framework/Frameworks/ViceroyTrace.framework/ViceroyTrace (0x13490b4d0) and /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/Library/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/PrivateFrameworks/AVConference.framework/AVConference (0x133a37e38). One of the two will be used. Which one is undefined.
。
发生这种情况时，我找不到任何具体方案，也没有找到重现问题的任何步骤。
