Android Studio: Design editor is unavailable until a successful build problem handling

Tried several solutions, hereby record:

1. Restart Android Studio (can solve most inexplicable reasons);
2. Build => Clear Project => Rebulid Project ;
3. File => Sync Project with Gradle Files;
4. The version of the referenced public class library does not match the version of the SDK. Solution ①: Gradle Scripts => build.gradle (name of the referenced public class library), change the Version to be consistent with the SDK, as shown in the figure below: ②Download is consistent with the version of the public class
   library the SDK.

In the afterword, the problems I encountered were solved using ② of solution 4.