wpf 无法在设计器中创建“[用户控件]”错误的实例
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Cannot create an instance of "[user control]" error in designer
提问by Rob McCabe
I have created the following user control. When I add it to a xaml window, I get the error "Cannot create an instance of "ucAppItem". I dragged the user control onto the window from the toolbar.
我创建了以下用户控件。当我将它添加到 xaml 窗口时，出现错误“无法创建“ucAppItem”的实例。我将用户控件从工具栏拖到窗口上。
XAML of user control is as follows:
用户控件的XAML如下：
<UserControl x:Class="Demos.ucAppItem"
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" Width="852" Height="215">
<Grid>
<Label Name="lblTitle" Content="Title" HorizontalAlignment="Left" Margin="233,10,0,0" VerticalAlignment="Top" FontSize="22" FontFamily="Arial"/>
<Image Width="40" Height="40" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0,0,80,0">
<Image.Style>
<Style TargetType="{x:Type Image}">
<Setter Property="Source" Value="pack://siteoforigin:,,,/arrow2.png"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Source" Value="pack://siteoforigin:,,,/arrow1.png"/>
</Trigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>
<Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" Foreground="#FF2EAADC" FontSize="20">
<Label.Style>
<Style TargetType="{x:Type Label}">
<Setter Property="Foreground" Value="#FF2EAADC"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Foreground" Value="#006d9e"/>
</Trigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
</Grid>
</UserControl>
XAML of window is as follows:
窗口的XAML如下：
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Demos" x:Class="Demos.Window1"
Title="Window1" Height="487" Width="854">
<Grid>
<local:ucAppItem/>
</Grid>
</Window>
Thanks for your help in advance!
提前感谢您的帮助！
采纳答案by Rob McCabe
@Anatoily Nikolaev - thanks for your help! Your pointer on the label fixed the issue I had with it and you were right about the image. I'll mark your response as the answer. It was the source that was the issue.
@Anatoily Nikolaev - 感谢您的帮助！您在标签上的指针解决了我遇到的问题，您对图像的看法是正确的。我会将您的回复标记为答案。这是问题的来源。
My label is now defined as:
我的标签现在定义为：
<Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" FontSize="20">
<Label.Style>
<Style TargetType="{x:Type Label}">
<Setter Property="Foreground" Value="#FF2EAADC"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Foreground" Value="#006d9e"/>
</Trigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
My image is now defined as:
我的形象现在被定义为：
<Image>
<Image.Style>
<Style TargetType="{x:Type Image}">
<Setter Property="Source" Value="{StaticResource arrow2}"/>
<Setter Property="Height" Value="40"/>
<Setter Property="Width" Value="40"/>
<Setter Property="VerticalAlignment" Value="Center"/>
<Setter Property="Margin" Value="0,0,80,0"/>
<Setter Property="HorizontalAlignment" Value="Right"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Source" Value="{StaticResource arrow1}"/>
</Trigger>
</Style.Triggers>
</Style>
</Image.Style>
</Image>
And I have resources (set in the App.xaml file), set as this:
我有资源（在 App.xaml 文件中设置），设置如下：
<Application x:Class="demos.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<BitmapImage x:Key="arrow1" UriSource="arrow1.png" />
<BitmapImage x:Key="arrow2" UriSource="arrow2.png" />
</Application.Resources>
</Application>
回答by Anatoliy Nikolaev
First, instead of pack://siteoforigin:,,,/arrow2.pngneed to write your actual URIand to make sure that the file exists in the project as a resource, like this (MSDN):
首先，pack://siteoforigin:,,,/arrow2.png不需要编写您的实际URI文件并确保该文件作为资源存在于项目中，像这样 ( MSDN)：
pack://application:,,,/arrow1.png
Secondly, trigger style for the label lblRun, will not work because you set this Foregroundvalue locally, in WPF have a list of value precedence (MSDN), that the local value of a higher priority than the trigger style:
其次，标签的触发器样式lblRun，将不起作用，因为你Foreground在本地设置了这个值，在 WPF 中有一个值优先级列表 ( MSDN)，即本地值的优先级高于触发器样式：
<Label x:Name="lblRun" Foreground="#FF2EAADC" FontSize="20" ... />
Try to remove it Foregroundlocal value and use Stylesetter:
尝试删除它的Foreground本地值并使用Stylesetter：
<Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" FontSize="20">
<Label.Style>
<Style TargetType="{x:Type Label}">
<Setter Property="Foreground" Value="#FF2EAADC"/>
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Foreground" Value="#006d9e"/>
</Trigger>
</Style.Triggers>
</Style>
</Label.Style>
</Label>
