报错：Gradle sync failed: com.android.tools.idea.gradle.project.sync.idea.issues.SdkPlatformNotFoundException: Module: 'app' platform 'android-29' not found.
解决：https://blog.csdn.net/weixin_43210113/article/details/109164430
解决：https://blog.csdn.net/weixin_43210113/article/details/109164430