Issue 1:
Sometimes I got this message:

The following assertion was thrown during a scheduler callback:

Child with id 73 is invisible and should not be added to the tree.

'package:flutter/src/semantics/semantics.dart': Failed assertion: line 671 pos 16:

'!child.isInvisible'

How can I debug this error? Is there any way to dump all widgets from the tree?

[✓] Flutter (on Mac OS X 10.13.2 17C88, locale en-HK, channel master)

• Flutter at /Users/odd/wa/flutter/flutter

• Framework revision 235b64e (2 weeks ago), 2017-12-14 20:38:39 -0800

• Engine revision e0d19e2

• Tools Dart version 1.25.0-dev.11.0

• Engine Dart version 2.0.0-edge.cf1de7d46cd88e204380e8f96a993439be56b24c

[✓] Android toolchain - develop for Android devices (Android SDK 26.0.3)

• Android SDK at /Users/odd/Library/Android/sdk

• Android NDK location not configured (optional; useful for native profiling support)

• Platform android-26, build-tools 26.0.3

• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java

• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-915-b08)

[✓] iOS toolchain - develop for iOS devices (Xcode 9.2)

• Xcode at /Applications/Xcode.app/Contents/Developer

• Xcode 9.2, Build version 9C40b

• ios-deploy 1.9.2

• CocoaPods version 1.3.1

[✓] Android Studio (version 3.0)

• Android Studio at /Applications/Android Studio.app/Contents

• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-915-b08)

[✓] IntelliJ IDEA Community Edition (version 2017.3)

• Flutter plugin version 20.0.3

• Dart plugin version 173.3727.108

[✓] Connected devices

• iPhone X • A786CB0E-0BD0-4698-919A-7440CFEDDD17 • ios • iOS 11.2 (simulator)

Issue 2:
Exception

══╡ EXCEPTION CAUGHT BY SCHEDULER LIBRARY ╞═════════════════════════════════════════════════════════
The following assertion was thrown during a scheduler callback:
Child with id 36 is invisible and should not be added to tree.
'package:flutter/src/semantics/semantics.dart': Failed assertion: line 370 pos 16:
'!child.isInvisible'

Either the assertion indicates an error in the framework itself, or we should provide substantially
more information in this error message to help you determine and fix the underlying cause.
In either case, please report this assertion by filing a bug on GitHub:
https://github.com/flutter/flutter/issues/new

When the exception was thrown, this was the stack:
════════════════════════════════════════════════════════════════════════════════════════════════════

flutter analyze

Analyzing /Users/hao/Documents/flutter_proj/shop...
No issues found!
Ran in 5.8s

Flutter Doctor

[✓] Flutter (on Mac OS X 10.13.1 17B1003, locale zh-Hans-CN, channel alpha)
• Flutter at /Users/hao/Documents/flutter
• Framework revision d957c8f040 (3 days ago), 2017-11-30 13:29:59 -0800
• Engine revision 77d8acb9be
• Tools Dart version 1.25.0-dev.11.0
• Engine Dart version 2.0.0-dev.9.0

[✓] Android toolchain - develop for Android devices (Android SDK 25.0.3)
• Android SDK at /Users/hao/Library/Android/sdk
• Unable to locate Android NDK.

• Unable to locate compiler in Android NDK.

• Platform android-25, build-tools 25.0.3
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] iOS toolchain - develop for iOS devices (Xcode 9.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 9.1, Build version 9B55
• ios-deploy 1.9.2
• CocoaPods version 1.3.1

[✓] Android Studio (version 2.3)
• Android Studio at /Applications/Android Studio.app/Contents
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] Connected devices
• iPhone 6s • AB7E1A1A-2F6B-469E-BA9F-BFAFA8C9A288 • ios • iOS 11.1 (simulator)

What does this exception mean?