访问ControlTemplate内部的元素

需要用到code behind

注意要给需要访问的元素命名x:Name="PART_TextBlock"

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:CustomControlLib">


    <Style TargetType="{x:Type local:MyControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:MyControl}">
                    <Border Background="{TemplateBinding Background}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}">
                        <StackPanel>
                            <TextBlock x:Name="PART_TextBlock" />
                        </StackPanel>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

custom control的程序部分

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace CustomControlLib
{
    
    public class MyControl : Button
    {
        private const string TextBlockPart = "PART_TextBlock";
        TextBlock textBlock;
        static MyControl()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(MyControl), new FrameworkPropertyMetadata(typeof(MyControl)));
        }
        public override void OnApplyTemplate() //OnApplyTemplate get called everytime a template is applied to the control,control update
        {
            base.OnApplyTemplate(); //Button有自己的OnApplyTemplate我们需要call这个beofre call我们自己写的OnApplyTemplate方法
            if (textBlock != null) //避免memory leak每次call OnApplyTemplate方法时都给同一个textBlock加上event
            {
                textBlock.TextInput -= new TextCompositionEventHandler(textBlock_TextInput);
            }
            
            textBlock = GetTemplateChild(TextBlockPart) as TextBlock;
            if (textBlock != null)
            {
                textBlock.Text = "Set from code";
                textBlock.TextInput +=new TextCompositionEventHandler(textBlock_TextInput);
            }
                
        }

        private void textBlock_TextInput(object sender, TextCompositionEventArgs e)
        {
            
        }
    }
}

使用该control
<Window x:Class="CustomControlDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:cc="clr-namespace:CustomControlLib;assembly=CustomControlLib"
        Title="MainWindow"
        Width="525"
        Height="350">
    <Grid>
        <cc:MyControl />
    </Grid>
</Window>

改进：上面的方法不好，设想如果controlTemaplte里有很多element都需要访问，每一个元素都需要后台程序这样访问的话，会很乱

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace CustomControlLib
{
    [TemplatePart(Name = TextBlockPart, Type = typeof(TextBlock))] //告诉使用template的作者这里x:Name为PART_TextBlock的control一定要是TextBlock类型的
    public class MyControl : Button
    {
        private const string TextBlockPart = "PART_TextBlock";
        TextBlock _textBlock; //避免每一次call OnApplyTemplate都在方法体里创建一个TextBlock，在方法前定义一个变量来储存
        protected TextBlock TextBlock
        {
            get {return _textBlock; }
            set
            {
                if (_textBlock != null) //避免memory leak每次call OnApplyTemplate方法时都给同一个textBlock加上event
                {
                    _textBlock.TextInput -= new TextCompositionEventHandler(textBlock_TextInput);
                }

                _textBlock = value;

                if (_textBlock != null)
                {
                    _textBlock.Text = "Set from code";
                    _textBlock.TextInput += new TextCompositionEventHandler(textBlock_TextInput);
                }
            }
        }
        static MyControl()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(MyControl), new FrameworkPropertyMetadata(typeof(MyControl)));
        }
        public override void OnApplyTemplate() //OnApplyTemplate get called everytime a template is applied to the control,control update
        {
            base.OnApplyTemplate(); //Button有自己的OnApplyTemplate我们需要call这个beofre call我们自己写的OnApplyTemplate方法
            
            TextBlock = GetTemplateChild(TextBlockPart) as TextBlock; //每次call都赋值属性 
        }

        private void textBlock_TextInput(object sender, TextCompositionEventArgs e)
        {
            
        }
    }
}

TemplatePart(Name="PART_Decrease", Type=typeof(RepeatButton))

一直没明白这是干嘛用的，搜了一下，记载一下。

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);
    }
}

 [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。

所以说白了，就是提示用的.....这么写比较规范。