TemplatePart作用



以Button的定义为例：

namespace System.Windows.Controls
{
    // Summary:
    //     Represents a button control, which reacts to the Click event.
    [TemplatePart(Name = "Normal State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "MouseOver State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "RootElement", Type = typeof(FrameworkElement))]
    [TemplatePart(Name = "Pressed State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "FocusVisualElement", Type = typeof(UIElement))]
    [TemplatePart(Name = "Disabled State", Type = typeof(Storyboard))]
    public class Button : ButtonBase
    {
        // Summary:
        //     Initializes a new instance of the Button class.
        public Button();
        // Summary:
        //     Apply a template to the Button.
        protected override void OnApplyTemplate();
        //
        // Summary:
        //     Called when the IsEnabled property changes.
        //
        // Parameters:
        //   isEnabled:
        //     New value of the IsEnabled property.
        protected override void OnIsEnabledChanged(bool isEnabled);
    }
}

namespace System.Windows.Controls
{
    // Summary:
    //     Represents a button control, which reacts to the Click event.
    [TemplatePart(Name = "Normal State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "MouseOver State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "RootElement", Type = typeof(FrameworkElement))]
    [TemplatePart(Name = "Pressed State", Type = typeof(Storyboard))]
    [TemplatePart(Name = "FocusVisualElement", Type = typeof(UIElement))]
    [TemplatePart(Name = "Disabled State", Type = typeof(Storyboard))]
    public class Button : ButtonBase
    {
        // Summary:
        //     Initializes a new instance of the Button class.
        public Button();
        // Summary:
        //     Apply a template to the Button.
        protected override void OnApplyTemplate();
        //
        // Summary:
        //     Called when the IsEnabled property changes.
        //
        // Parameters:
        //   isEnabled:
        //     New value of the IsEnabled property.
        protected override void OnIsEnabledChanged(bool isEnabled);
    }
}

 [TemplatePart(Name = "Normal State", Type = typeof(Storyboard))] 这种东东是做什么用的 ， 其实这是一种契约 ， 是一种推荐的控件设计模式（只是推荐） ， 意思是告诉要来写ControlTemplate的用户 ， 你的ControlTemplate中需要有一个x:Name为“Normal State” , 类型为Storyboard ， 当然这个类型可以是继承来的， 为什么一定要包含这些契约规定的元素 ， 因为逻辑部分对这些东西进行了引用，它们将对控件的默认行为起着关键作用， 可以理解为这个控件的最基本元素 ， 是实现默认行为的最小集合， 自然，你的ControlTemplate中如果没有包含契约中的内容 ， 则相应的逻辑将无法实现。