Describes the configuration for an [Element].
描述元素的配置
Widgets are the central class hierarchyin the Flutter framework.
组件是 Flutter Framework 层次结构中的中心类
A widget is an immutable description of part of a user interface
控件是用户界面****不可变描述的一部分
Widgets can be inflated into elements, which manage the underlying****render tree.
控件能被解析到元素列表中，被底层****呈现树管理
Widgets themselves have no mutable state (all their fields must be final).
If you wish to associate mutable state with a widget, considerusing a
StatefulWidget\], which creates a \[State\] object (via \[StatefulWidget.createState\]) whenever it is inflated into an element and **incorporated**into the tree. 控件自身拥有不可变状态（他们的属性必须是final），如果你希望关联到一个可变状态的控件，请**考虑**使用\[StatefulWidget\]，创建一个\[State\] 类（通过StatefulWidget.createState），不管如何，他会被解析成元素**合并**到树中 **A given widget**can be included in the tree zero or more times.**In particular** a given widget can be placed in the tree multiple times. Each time a widget is placed in the tree, it is inflated into an \[Element\], which means a widget that is incorporated into the tree multiple times will be inflated multiple times. **给定的小部件**可以在树中包含零次或多次。**特别是**给定的小部件可以多次放置在树中。每次一个小部件被放置在树中，它被解析成一个\[Element\]，这意味着一个多次合并到树中的小部件将被充气 很多次了。 The \[key\] property controls how one widget replaces another widget in the tree. If the \[runtimeType\] and \[key\] properties of the two widgets are \[operator==\], **respectively**, then the new widget replaces the old widget by updating the underlying element (i.e., by calling \[Element.update\] with the new widget). **Otherwise**, the old element is removed from the tree, the new widget is inflated into an element, and the new element is inserted into the tree. \[key\]属性控制一个小部件如何替换树中的另一个小部件。如果两个小部件的\[runtimeType\]和\[key\]属性分别为\[operator==\]，则新小部件**依次**通过更新底层元素（即通过调用\[element\]）来替换旧小部件。用新的小部件更新)。**否则**，将从树中删除旧元素，将新小部件解析为元素，并将新元素插入到树中。 \[StatefulWidget\] and \[State\], for widgets that can build differently**several times**over their lifetime. \[StatefulWidget\]和\[State\]，用于在其生命周期中可以**多次**构建不同的小部件。 \[InheritedWidget\], for widgets that **introduce ambient**state that can be read by **descendant**widgets. 这个控件**引入环境** 状态它能够被**子**控件读取 \[StatelessWidget\], for widgets that always build the same way given a **particular**configuration and **ambient**state. \[StatelessWidget\]，用于在给定**特定**配置和**环境**状态时始终以相同方式构建的小部件。