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======== Exception caught by widgets library =======================================================
The following assertion was thrown building Text("动画状态 : null"):
No Directionality widget found.

RichText widgets require a Directionality widget ancestor.

The specific widget that could not find a Directionality ancestor was: RichText
  softWrap: wrapping at box width
  maxLines: unlimited
  text: "动画状态 : null"
  dirty
The ownership chain for the affected widget is: "RichText ← Text ← Column ← Padding ← Container ← AnimationApp ← [root]"

Typically, the Directionality widget is introduced by the MaterialApp or WidgetsApp widget at the top of your application widget tree. It determines the ambient reading direction and is used, for example, to determine how to lay out text, how to interpret "start" and "end" values, and to resolve EdgeInsetsDirectional, AlignmentDirectional, and other *Directional objects.

The relevant error-causing widget was: 
  Text file:///D:/002_Project/002_Android_Learn/flutter_animation/lib/main.dart:118:11
When the exception was thrown, this was the stack: 
#0      debugCheckHasDirectionality.<anonymous closure> (package:flutter/src/widgets/debug.dart:272:7)
#1      debugCheckHasDirectionality (package:flutter/src/widgets/debug.dart:292:4)
#2      RichText.createRenderObject (package:flutter/src/widgets/basic.dart:5539:37)
#3      RenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5423:28)
#4      MultiChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6166:11)
...
====================================================================================================

======== Exception caught by widgets library =======================================================
No Directionality widget found.
The relevant error-causing widget was: 
  Text file:///D:/002_Project/002_Android_Learn/flutter_animation/lib/main.dart:120:11
====================================================================================================

======== Exception caught by rendering library =====================================================
A RenderFlex overflowed by 199358 pixels on the bottom.
The relevant error-causing widget was: 
  Column file:///D:/002_Project/002_Android_Learn/flutter_animation/lib/main.dart:96:14
====================================================================================================

Text("动画状态 : $animationStatus"),
Text("动画值 : $animationValue"),

Text("动画状态 : $animationStatus", textDirection: TextDirection.ltr,),
Text("动画值 : $animationValue", textDirection: TextDirection.ltr,),