How to dissolve ui with all childs

[HuismanKwl]

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Environment (please complete the following information):

• Version [e.g. 4.0.0]
• Platform: [e.g. Editor(Windows/Mac), Standalone(Windows/Mac), iOS, Android, WebGL]
• Unity version: [e.g. 2018.2.8f1]
• Build options: [e.g. IL2CPP, .Net 4.x, LWRP]

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