自定义WPF / XAML画布 [英] Custom WPF/XAML Canvas

问题描述

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

I'm trying to create and use a custom Canvas. Here is the 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）：

Here is the code declaration (MyCanvas.xaml.cs):

public partial class MyCanvas : Canvas

当我尝试像这样使用它时：

When I try to use it like so:

<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>

我遇到两个不同的错误：

I get two different errors:

内容属性只能设置一次。 ==>它不是继承Canvas吗？！？！？！

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

成员 Top未被识别或无法访问。 ==>是不是再次继承了Canvas？！？！？！
成员 Left未被识别或无法访问。 ==>是不是再次继承了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：这就是我的意思远...仍在获取内容已设置错误！

MyCanvas.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: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

MyCanvas.xaml.cs

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

MainWindow.xaml

MainWindow.xaml

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

推荐答案

左和 Top 是附加属性。这意味着它们不会被您的类继承。

Left and Top are attached properties. That means that they are not inherited by your class.

您需要更改用户控件声明以使用 Canvas.Left 和 Canvas.Top 代替：

You need to change the user control declaration to use Canvas.Left and Canvas.Top instead:

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

内容的问题是您将其设置了两次，就像错误消息中说的那样。

The problem with the content is that you set it twice, just like the error message says.

1. 在 MyCanvas.xaml 中，将其设置为 Image 。


2. 使用时，将其设置为用户控件。

1. In MyCanvas.xaml you set it to an Image.
2. When using it, you set it to your user controls.

要对其进行修复，您需要在 MyCanvas 中添加 ItemsControl 并将其声明为表示内容的控件：

To fix it, you need to add an ItemsControl to MyCanvas and declare it as the control that represents the content:

<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>

在您的课程文件中：

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

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