WPF/Silverlight 中的 UIElement 与 FrameworkElement [英] UIElement vs FrameworkElement in WPF/Silverlight

问题描述

考虑到 FrameworkElement 继承 UIElement，我什么时候从 UIElement 和 FrameworkElement 派生.谁能举出真实的例子?

When do I derive from UIElement and FrameworkElement considering FrameworkElement inherits UIElement. Can anyone give real life examples?

推荐答案

这是一个学习 WPF 架构的好页面，这个答案只适用于 WPF.如果您有时间，请查看 UIElement 和 FrameworkElement 部分，以及其余部分.这是链接页面的引述，解释了为什么存在 2 个级别:

This is a good page for learning about WPF Architecture, and this answer only applies to WPF. Check out the UIElement and FrameworkElement sections, as well as the rest if you have time. Here's a quote from the linked page explaining why the 2 levels exist:

到本主题的这一点，WPF 的核心"特性——在 PresentationCore 程序集中实现的特性，一直是焦点.在构建 WPF 时，基础部分(如使用 Measure 和Arrange 的布局合同)和框架部分(如网格等特定布局的实现)之间的清晰分离是期望的结果.目标是在堆栈中提供一个低扩展点，允许外部开发者在需要时创建自己的框架.

To this point in the topic, "core" features of WPF – features implemented in the PresentationCore assembly, have been the focus. When building WPF, a clean separation between foundational pieces (like the contract for layout with Measure and Arrange) and framework pieces (like the implementation of a specific layout like Grid) was the desired outcome. The goal was to provide an extensibility point low in the stack that would allow external developers to create their own frameworks if needed.

简而言之，UIElement 知道如何绘制自己(因为它们源自 Visual).他们还可以通过提供像 OnPreviewMouseDown 和 OnMouseDown，以及 布局系统通过实现Measure和Arrange.

In short, UIElements know how to draw themselves (because they are derived from Visual). They can also use the routed events system by providing virtual methods like OnPreviewMouseDown and OnMouseDown, and part of the layout system by implementing Measure and Arrange.

FrameworkElement 通过实现一些在 UIElement 中定义的虚拟方法来扩展布局系统.它们提供了设置布局属性的一致方式，例如Margin 属性和 MinWidth 属性.此外，可以设置样式，并且它们可以参与数据绑定.

FrameworkElements extend the layout system by implementing some of the virtual methods defined in UIElement. They provide a consistent way of setting layout properties, e.g. the Margin property and the MinWidth property. Additionally, the can be styled, and they can take part in data binding.

回答您的问题，如果您需要 FrameworkElement 添加的任何额外功能，例如您需要更易于使用的样式、绑定或布局系统，然后从中派生.否则，从 UIElement 派生，因为使用 FrameworkElement 会产生轻微的开销.

In answer to your question, if you need any of the extra abilities that FrameworkElement add, e.g. you need styles, binding or a layout system that's easier to use, then derive from them. Otherwise, derive from UIElement as there is a slight overhead from using FrameworkElement.

此外，您应该查看 Control 类(派生自 FrameworkElement)，因为它们提供了有用的新功能层，例如 模板和Padding等属性.

Also, you should have a look at the Control class (derived from FrameworkElement), as these provide useful new layers of functionality like Templating and properties like Padding.

熟悉继承层次结构也是一个好主意，您可能希望从其中的其他类派生(尽管可能不会比 Visual 更高).

Familiarising yourself with the inheritance hierarchy is also a good idea, you might want to derive from other classes in it (though probably no higher up the chain than Visual).

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