自定义控件：如何覆盖默认属性？

Question

我创建了一个类似于按钮的自定义控件。我想覆盖他的默认属性，但效果很奇怪。

用户控件Xaml

<UserControl x:Class="project.MyButton"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d" 
             d:DesignHeight="50" d:DesignWidth="50">
    <Grid>
        <Ellipse x:Name="structure" Fill="Black" Stroke="White" StrokeThickness="2"/>
        <Label x:Name="content" Content="&#xE081;" VerticalAlignment="Center" HorizontalAlignment="Center" Foreground="White" FontFamily="Segoe MDL2 Assets" FontWeight="Bold" FontSize="16"/>
    </Grid>
</UserControl>

UserControl 代码隐藏 (C#)

    /// <summary>A simple custom button.</summary>
    public partial class MyButton : UserControl
    {
        /// <summary>Background color.</summary>
        public new Brush Background { get => structure.Fill; set => structure.Fill = value; }

        /// <summary>Foreground color.</summary>
        public new Brush Foreground { get => content.Foreground; set => content.Foreground = value; }

        /// <summary>Stroke color.</summary>
        public Brush Stroke { get => structure.Stroke; set => structure.Stroke = value; }

        /// <summary>Stroke thickness.</summary>
        public double StrokeThickness { get => structure.StrokeThickness; set => structure.StrokeThickness = value; }

        /// <summary>Font family.</summary>
        public new FontFamily FontFamily { get => content.FontFamily; set => content.FontFamily = value; }

        /// <summary>Font weight.</summary>
        public new FontWeight FontWeight { get => content.FontWeight; set => content.FontWeight = value; }

        /// <summary>Font size.</summary>
        public new double FontSize { get => content.FontSize; set => content.FontSize = value; }

        /// <summary>Content.</summary>
        public new object Content { get => content.Content; set => content.Content = value; }


        /// <summary>Inizialize new <see cref="MyButton"/>.</summary>
        public MyButton()
        {
            InitializeComponent();
        }
    }

结果

但是，当我尝试设置背景时属性它会为控件的背景着色，而不是椭圆，当我尝试设置内容时，它会覆盖按钮等...

示例：Background="Red"

Answer 1

UserControl 有其 Backround 和 Content 属性，它们是 DependencyProperties 的包装器。

您试图在属性之前使用 new 关键字隐藏它们，但失败了。 (在setter中设置断点：永远不会命中断点)

当从 xaml 设置 Background="smth" 或 Content="smth" 时，检测基本属性，此外 WPF 不使用包装器属性，它直接使用 DependencyObject.SetValue()。设置基本内容只是简单地删除现有的带椭圆的网格。

重命名背景 -> CustomBackground、内容 -> CustomContent 并设置它们。然后 MyButton 将起作用。

更好的方法是重用基础内容和背景（将它们绑定到 MyButton xaml 中的 Ellipse 和 Lable）。

Answer 2

您可以为 UserControl 定义一个 ControlTemplate:

<UserControl x:Class="project.MyButton"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WpfApp4"
             mc:Ignorable="d" 
             d:DesignHeight="50" d:DesignWidth="50">
    <UserControl.Template>
        <ControlTemplate TargetType="UserControl">
            <Grid>
                <Ellipse x:Name="structure" Fill="{TemplateBinding Background}" Stroke="White" StrokeThickness="2"/>
                <Label x:Name="content" Content="{TemplateBinding Content}" VerticalAlignment="Center" HorizontalAlignment="Center" Foreground="White" FontFamily="Segoe MDL2 Assets" FontWeight="Bold" FontSize="16"/>
            </Grid>
        </ControlTemplate>
    </UserControl.Template>
</UserControl>

在模板中使用 TemplateBinding 作为 en 元素的属性，您可以设置 UserControl 的属性来更改属性模板中元素的数量：

<local:Button Background="Red" Content="&#xE081;" />

自定义控件：如何覆盖默认属性？

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