导致这个错误的另一个常见原因是:

Right click on folder in project to create new UserControl. This creates a class and xaml file that derives from user control in the namespace of the folder. Then you decide to change the namespace of the class because you're really just using folders for organization of code. The x:Class attribute will not get automatically updated so it will be searching for a class that doesn't exist. Could probably use a better error message like "x:Class type could not be found in namesace bla.blaa.blaaa."

I know this was answered due to a different cause, but this is a highly hit posting and I had ran into the same issue with a class library. In this case, it turned out to be both a change in my namespace (answered in this post here) and that the compiler could not rebuild the Window.g.i.cs which defines the InitializeComponent() method. It couldn't because the class library was missing the ProjectTypeGuid value for WPF projects in the csproj file. Instructions for this are here and here. I thought I would share in case someone else has run into the same issue. Just changing the namespace isn't enough in this case.

另一种可能的解释是，您正在针对x86进行构建。右键单击解决方案并选择配置管理器。看看你是否在x86而不是任何CPU上构建。

在我的案例中(NET Core 3.1)，我通过在项目文件的ProjectGroup部分中给它一个AssemblyName标记来修复它。如。

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <UseWPF>true</UseWPF>
    <AssemblyName>ProjectNameUsually</AssemblyName>
  </PropertyGroup>
  ...
</Project>

这也修复了编译器在代码背后看不到x:Name控件的问题。

如果命名空间是正确的，那么也有一个相同的错误，

只需关闭应用程序并重新打开。

这也许能解决你的问题

此问题的另一个解决方案是简单地将属性-> Build Action从嵌入式资源更改为其他任何内容，保存，然后将其更改为嵌入式资源。错误消失了。