MaterialDesignTheme 5.x WPF使用报IOException: 找不到资源“themes/materialdesigntheme.defaults.xaml”错误

问题出现

在WPF项目中使用MaterialDesignTheme框架美化界面，按照官方文档介绍，在App.xaml文件中引入如下代码：

<?xml version="1.0" encoding="UTF-8"?>
<Application . . .>
  <Application.Resources>
    <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml" />
        <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
        <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Primary/MaterialDesignColor.DeepPurple.xaml" />
        <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Accent/MaterialDesignColor.Lime.xaml" />
      </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
  </Application.Resources>
</Application>

并编写MainWindow.xaml代码如下：

<Window x:Class="AntiCadVirus.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:AntiCadVirus"
        mc:Ignorable="d"
        Title="MainWindow" Height="618" Width="1000"
        xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
        >
    <Grid>
        <materialDesign:Card>
            <TabControl VerticalContentAlignment="Bottom"  materialDesign:ColorZoneAssist.Mode="PrimaryMid" Style="{StaticResource MaterialDesignNavigationRailTabControl}">
                <TabItem Width="120" Height="120">
                    <TabItem.Header>
                        <StackPanel Width="auto" Height="auto">
                            <materialDesign:PackIcon Width="24" Height="24" HorizontalAlignment="Center" Kind="Folder" />
                            <TextBlock HorizontalAlignment="Center" Text="All Files" />
                        </StackPanel>
                    </TabItem.Header>
                    <StackPanel Margin="16">
                        <TextBlock Margin="0,0,0,8" Style="{StaticResource MaterialDesignHeadline5TextBlock}" Text="All files" />
                        <TextBlock>
                            <Run Text="tab 1 content. Default look and behaviors." />
                            <LineBreak />
                            <LineBreak />
                            <Run FontStyle="Italic">
                                Neque porro quisquam est qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit...
                            </Run>
                        </TextBlock>
                    </StackPanel>
                </TabItem>
                <TabItem>
                    <TabItem.Header>
                        <StackPanel Width="auto" Height="auto">
                            <materialDesign:PackIcon Width="24" Height="24" HorizontalAlignment="Center" Kind="ClockOutline" />
                            <TextBlock
                                HorizontalAlignment="Center" Text="Recent" />
                        </StackPanel>
                    </TabItem.Header>
                    <StackPanel Margin="16">
                        <TextBlock Margin="0,0,0,8" Style="{StaticResource MaterialDesignHeadline5TextBlock}" Text="Recent" />
                        <TextBlock>
                            <Run Text="tab 2 content. Default look and behaviors." />
                            <LineBreak />
                            <LineBreak />
                            <Run FontStyle="Italic">
                                Praesent sed dui arcu. Vivamus porta auctor sagittis
                            </Run>
                        </TextBlock>
                    </StackPanel>
                </TabItem>
                <TabItem>
                    <TabItem.Header>
                        <StackPanel Width="auto" Height="auto">
                            <materialDesign:PackIcon Width="24" Height="24" HorizontalAlignment="Center" Kind="Images" />
                            <TextBlock HorizontalAlignment="Center" Text="Photos" />
                        </StackPanel>
                    </TabItem.Header>
                    <StackPanel Margin="16">
                        <TextBlock Margin="0,0,0,8" Style="{StaticResource MaterialDesignHeadline5TextBlock}" Text="Photos" />
                        <TextBlock>
                            <Run Text="tab 3 content. Default look and behaviors." />
                            <LineBreak />
                            <LineBreak />
                        </TextBlock>
                    </StackPanel>
                </TabItem>
                <TabItem>
                    <TabItem.Header>
                        <StackPanel Width="auto" Height="auto">
                            <materialDesign:PackIcon Width="24" Height="24" HorizontalAlignment="Center" Kind="MusicBoxMultiple" />
                            <TextBlock HorizontalAlignment="Center" Text="Sounds" />
                        </StackPanel>
                    </TabItem.Header>
                    <StackPanel Margin="16">
                        <TextBlock Margin="0,0,0,8" Style="{StaticResource MaterialDesignHeadline5TextBlock}" Text="Sounds" />
                        <TextBlock>
                            <Run Text="tab 4 content. Default look and behaviors." />
                            <LineBreak />
                            <LineBreak />
                        </TextBlock>
                    </StackPanel>
                </TabItem>
            </TabControl>
        </materialDesign:Card>
    </Grid>
</Window>

编译及生成过程未见异常，但当运行时却不能正常出现窗体，使用调试方式运行，发现程序报找不到资源“themes/materialdesigntheme.defaults.xaml”错误：

显然，在5.1.1的MaterialDesignTheme（写这篇博客的时候用的是5.1.1版）中，并不存在资源：

<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesign3.Defaults.xaml" />

同样，另一个资源：

<ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Accent/MaterialDesignColor.Lime.xaml" />

在该版本中也不存在。

问题解决

查看官方仓库的迁移指引（参考资料1），发现在该版本中，App.xaml的引用内容要作一定调整：

<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesign3.Defaults.xaml" />

应修改为：

<ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesign3.Defaults.xaml" />

<ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Accent/MaterialDesignColor.Lime.xaml" />

则将Accent修改成Sencondary。
最后，App.xaml代码修改情况参考如下：

<Application ...>
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesign3.Defaults.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Primary/MaterialDesignColor.Blue.xaml" />
                <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Secondary/MaterialDesignColor.Lime.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

最终问题解决：

参考资料

[1] 5.0.0 Migration Guide