InheritedModel / InheritedWidget

https://flutter.institute/sharing-data-inheritedmodel-vs-inheritedwidget/
其工作原理为被其嵌套的子widget可以通过InheritedModel.inheritFrom获取到InheritedModel或者InheritedWidget

https://loveky.github.io/2018/07/18/how-flutter-inheritedwidget-works/

InheritedWidget.png Snip20190503_1.png

Element源码

this依赖于ancestor

@Deprecated(
    'Use dependOnInheritedElement instead. '
    'This feature was deprecated after v1.12.1.'
  )
  @override
  InheritedWidget inheritFromElement(InheritedElement ancestor, { Object aspect }) {
    return dependOnInheritedElement(ancestor, aspect: aspect);
  }

  @override
  InheritedWidget dependOnInheritedElement(InheritedElement ancestor, { Object aspect }) {
    assert(ancestor != null);
    _dependencies ??= HashSet<InheritedElement>();
    _dependencies.add(ancestor);
    ancestor.updateDependencies(this, aspect);
    return ancestor.widget;
  }

this依赖于指定类型widget的Element（ancestor）,并返回ancestor（也就是指定widget类型的element）的widget

@Deprecated(
    'Use dependOnInheritedWidgetOfExactType instead. '
    'This feature was deprecated after v1.12.1.'
  )
  @override
  InheritedWidget inheritFromWidgetOfExactType(Type targetType, { Object aspect }) {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[targetType];
    if (ancestor != null) {
      assert(ancestor is InheritedElement);
      return inheritFromElement(ancestor, aspect: aspect);
    }
    _hadUnsatisfiedDependencies = true;
    return null;
  }

  @override
  T dependOnInheritedWidgetOfExactType<T extends InheritedWidget>({Object aspect}) {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[T];
    if (ancestor != null) {
      assert(ancestor is InheritedElement);
      return dependOnInheritedElement(ancestor, aspect: aspect);
    }
    _hadUnsatisfiedDependencies = true;
    return null;
  }

查找指定类型widget的Element

@Deprecated(
    'Use getElementForInheritedWidgetOfExactType instead. '
    'This feature was deprecated after v1.12.1.'
  )
  @override
  InheritedElement ancestorInheritedElementForWidgetOfExactType(Type targetType) {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[targetType];
    return ancestor;
  }

  @override
  InheritedElement getElementForInheritedWidgetOfExactType<T extends InheritedWidget>() {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[T];
    return ancestor;
  }

查找指定类型的widget

@Deprecated(
    'Use findAncestorWidgetOfExactType instead. '
    'This feature was deprecated after v1.12.1.'
  )
  @override
  Widget ancestorWidgetOfExactType(Type targetType) {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    Element ancestor = _parent;
    while (ancestor != null && ancestor.widget.runtimeType != targetType)
      ancestor = ancestor._parent;
    return ancestor?.widget;
  }

  @override
  T findAncestorWidgetOfExactType<T extends Widget>() {
    assert(_debugCheckStateIsActiveForAncestorLookup());
    Element ancestor = _parent;
    while (ancestor != null && ancestor.widget.runtimeType != T)
      ancestor = ancestor._parent;
    return ancestor?.widget;
  }