17370845950

1. 前言

最近在自定义Expander的样式时，我顺便研究了它的源码。Expander控件是一个ContentControl，它通过IsExpanded属性或通过点击Header中的ToggleButton来控制内容的展开或隐藏。虽然UWP SDK本身并未提供此控件，但在UWP Community Toolkit中可以找到。它是一个经典的入门级控件，代码结构简单，虽然仍有改进空间，但非常适合学习如何自定义模板化控件。

2. 详解

代码语言：javascript

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[ContentProperty(Name = "Content")][TemplatePart(Name = "PART_RootGrid", Type = typeof(Grid))][TemplatePart(Name = "PART_ExpanderToggleButton", Type = typeof(ToggleButton))][TemplatePart(Name = "PART_LayoutTransformer", Type = typeof(LayoutTransformControl))][TemplateVisualState(Name = "Expanded", GroupName = "ExpandedStates")][TemplateVisualState(Name = "Collapsed", GroupName = "ExpandedStates")][TemplateVisualState(Name = "LeftDirection", GroupName = "ExpandDirectionStates")][TemplateVisualState(Name = "DownDirection", GroupName = "ExpandDirectionStates")][TemplateVisualState(Name = "RightDirection", GroupName = "ExpandDirectionStates")][TemplateVisualState(Name = "UpDirection", GroupName = "ExpandDirectionStates")]public class Expander : ContentControl{    public Expander();    public string Header { get; set; }    public DataTemplate HeaderTemplate { get; set; }    public bool IsExpanded { get; set; }    public ExpandDirection ExpandDirection { get; set; }    public event EventHandler Expanded;    public event EventHandler Collapsed;    public void OnExpandDirectionChanged();    protected override void OnApplyTemplate();    protected virtual void OnCollapsed(EventArgs args);    protected virtual void OnExpanded(EventArgs args);}