c# – 自定义WPF / XAML画布

发布时间：2020-12-16 01:52:56 所属栏目：百科来源：网络整理

导读：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:

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：这是我到目前为止…仍然得到“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
{
    // ...
}

MainWindow.xaml

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

解决方法

Left和Top是 attached properties.这意味着它们不会被你的类继承.

您需要更改用户控件声明以使用Canvas.Left和Canvas.Top：

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

内容的问题是您将其设置两次,就像错误消息所说的那样.

>在MyCanvas.xaml中,将其设置为图像.
>使用时,将其设置为用户控件.

要修复它,您需要将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>

在您的类文件中：

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

（编辑：李大同）

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