c# - 自定义 WPF/XAML Canvas

Question

我正在尝试创建和使用自定义 Canvas 。这是 XAML (MyCanvas.xaml):

<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:Core="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Namespace="clr-namespace:MyNamepace" xmlns:Properties="clr-namespace:MyNamepace.Properties" Core:Class="MyNamepace.MyCanvas">
    <Canvas.Resources>
        <Namespace:ImagesConverter Core:Key="ImagesConverter"/>
    </Canvas.Resources>
    <Image Source="{Binding Source={Core:Static Properties:Resources.Background}, Converter={StaticResource ImagesConverter}}" Stretch="Fill"/>
</Canvas>

这是代码声明 (MyCanvas.xaml.cs):

public partial class MyCanvas : Canvas

当我尝试像这样使用它时:

<Namespace:MyCanvas Core:Name="Layout" Loaded="OnLoaded">
    <Namespace:MyUserControl Core:Name="Control1" Namespace:MyCanvas.Left="50" MyProperty="50">
        <Namespace:MyCanvas.Top>
            <MultiBinding Converter="{StaticResource MathConverter}" ConverterParameter="(x - y) / 2">
                <Binding ElementName="Layout" Path="ActualHeight"/>
                <Binding Path="ActualHeight" RelativeSource="{RelativeSource Self}"/>
            </MultiBinding>
        </Namespace:MyCanvas.Top>
    </Namespace:MyUserControl>
    <Namespace:MyUserControl Core:Name="Control2" Namespace:MyCanvas.Left="744" Namespace:MyCanvas.Top="42" MyProperty="150"/>
</Namespace:MyCanvas>

我得到两个不同的错误:

The property "Content" can only be set once. ==> Isn't it inheriting Canvas?!?!?!

The member "Top" is not recognized or is not accessible. ==> Isn't it inheriting Canvas again?!?!?! The member "Left" is not recognized or is not accessible. ==> Isn't it inheriting Canvas again?!?!?!

编辑:这是我目前所拥有的...仍然出现“内容”已设置错误!

MyCanvas.xaml

<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:Core="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Namespace="clr-namespace:MyNamespace" xmlns:Properties="clr-namespace:MyNamespace.Properties" Core:Class="MyNamespace.MyCanvas">
    <Canvas.Background>
        <ImageBrush ImageSource="{Binding Source={Core:Static Properties:Resources.Background}, Converter={StaticResource ImagesConverter}}" Stretch="Fill"/>
    </Canvas.Background>
    <Canvas.Resources>
        <Namespace:ImagesConverter Core:Key="ImagesConverter"/>
    </Canvas.Resources>
</Canvas>

MyCanvas.xaml.cs

public class MyCanvas : Canvas
{
    // ...
}

主窗口.xaml

<Namespace:MyCanvas Core:Name="MyCanvas" Loaded="OnLoaded">
    <Namespace:MyUserControl ...
    <Namespace:MyUserControl ...
    <Namespace:MyUserControl ...
</Namespace:MyCanvas>

Answer 1

Left 和 Top 是 attached properties .这意味着它们不会被您的类继承。

您需要更改用户控件声明以改为使用 Canvas.Left 和 Canvas.Top:

<Namespace:MyUserControl Core:Name="Control2" Canvas.Left="744" Canvas.Top="42" 
                         MyProperty="150"/>

content的问题是你设置了两次，就像报错信息说的那样。

1. 在 MyCanvas.xaml 中，您将其设置为 Image。
2. 使用它时，您将其设置为您的用户控件。

要修复它，您需要将一个ItemsControl 添加到MyCanvas 并将其声明为表示内容的控件:

<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:Core="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Namespace="clr-namespace:MyNamepace" xmlns:Properties="clr-namespace:MyNamepace.Properties" Core:Class="MyNamepace.MyCanvas">
    <Canvas.Resources>
        <Namespace:ImagesConverter Core:Key="ImagesConverter"/>
    </Canvas.Resources>
    <Image Source="{Binding Source={Core:Static Properties:Resources.Background}, Converter={StaticResource ImagesConverter}}" Stretch="Fill"/>
    <ItemsControl Content="{Binding Path=LocalContent, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type Namespace:MyCanvas}}}" />
</Canvas>

在你的类文件中:

[ContentProperty("LocalContent")]
public partial class MyCanvas : Canvas
{
    public static readonly DependencyProperty LocalContentProperty =
        DependencyProperty.Register(
            "LocalContent", 
            typeof(UIElementCollection), 
            typeof(MyCanvas ), 
            new PropertyMetadata(default(UIElementCollection)));
}