What does MissingManifestResourceException mean and how to fix it?

Question

All I needed to do to fix this problem was to right-click the Resources.resx file in the Solution Explorer and click Run Custom Tool. This re-generates the auto-generated Resources.Designer.cs file.

If the .resx file was added to the project manually, the Custom Tool property of the file must be set to "ResXFileCodeGenerator".

The problem is due to a mismatch of namespaces, which occurs if you change the "default namespace" of the assembly in the project settings. (I changed it from (previously) "Servers" to (now) "RT.Servers".)

In the auto-generated code in Resources.Designer.cs, there is the following code:

internal static global::System.Resources.ResourceManager ResourceManager {
    get {
        if (object.ReferenceEquals(resourceMan, null)) {
            global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("Servers.Resources", typeof(Resources).Assembly);
            resourceMan = temp;
        }
        return resourceMan;
    }
}

The literal string "Servers.Resources" had to be changed to "RT.Servers.Resources". I did this manually, but running the custom tool would have equally well done it.

I just came across this problem today, and I found this Microsoft Help and Support page that actually did work around the problem.

I had a couple delegates at the top of my file, in the global namespace, and all of a sudden I was getting a MissingManifestResourceException when running the program, on this line:

this.Icon = ((System.Drawing.Icon)(resources.GetObject("$this.Icon")));

Then I moved the delegates into the namespace, got the same error. Finally I put the delegates in the only class in that file, and the error went away, but I didn't want the delegates in that class or namespace.

Then I came across that link above, which said

To resolve this problem, move all of the other class definitions so that they appear after the form's class definition.

I put the delegates (which I would not consider "class definitions") at the bottom of that file, outside of the local namespace, and the program didn't get the MissingManifestResourceException anymore. What an irritating error. But, that seems like a more robust solution than modifying the auto-generated code :)

I've run into a similar issue and, although I know it isn't the cause the OP had, I'll post it here so that if someone else runs across this problem in the future, an answer will be available.

If you add a class before the designer class you will get a MissingManifestResourceException exception at runtime (no compile time error or warning) because

Visual Studio requires that designers use the first class in the file.

For (slightly) more information see this post.

I had the same problem, but using the Run Custom Tool command as suggested by Timwi did not help in my case.

However it lead me into the right direction, because I ended up in the Properties of the .resx file. Here I noticed a difference to another .resx file that caused no problems.

In my case I had to change the property "Build Action" from "Resource" to "Embedded Resource".

My best guess for the reason is, that I had the .resx in a library that was used from another application. My application did not have its own .resx file, so it had to use the one from the library - which is only available when it's embedded in the library and not "stand alone".

When I run in a similar issue, in Vs 2012, it turned out that the "Custom Tool Namespace" property of the resx file was wrong (in my case, actually, it was unset, so the generated code yeld this exception at runtime). My final set of properties for the resx file was something like this:

• Build action: Embedded Resource
• Copy to Output Directory: Do not copy
• Custom Tool: ResXFileCodeGenerator
• Custom Tool Namespace: My.Project.S.Proper.Namespace

Also see: MissingManifestResourceException when running tests after building with MSBuild (.mresource has path in manifest)

I repeat the answer here just for completeness:

It appears adding LogicalName to the project file fixes it:

<LogicalName>$(RootNamespace).Properties.Resources.resources</LogicalName> 

i.e. so the embedded resource entry in the project file looks like this:

<ItemGroup>
  <EmbeddedResource Include="Properties\Resources.resx">
    <Generator>ResXFileCodeGenerator</Generator>
    <LastGenOutput>Resources.Designer.cs</LastGenOutput>
    <LogicalName>$(RootNamespace).Properties.Resources.resources</LogicalName> 
  </EmbeddedResource>
</ItemGroup>

This is detailed in: http://blogs.msdn.com/b/msbuild/archive/2007/10/19/manifest-resource-names-changed-for-resources-files.aspx

Note that we are using a .resx file, but the bug still appears to occur.

Update: The problem with resources (incl. XAML) appears to be related to output paths and the use of forward or backward slashes as detailed in: Why does modifying project output directories cause: IOException was unhandled "Cannot locate resource 'app.xaml'."

I ran into a different cause of this problem, which was unrelated to resx files. I had a class library where AssemblyInfo.cs contained the following:

[assembly: ThemeInfo(
ResourceDictionaryLocation.SourceAssembly,
ResourceDictionaryLocation.SourceAssembly)]

The assembly did not contain any WPF code, theme or Resource dictionaries. I got rid of the exception by removing the ThemeInfo attribute.

I did not get an actual exception, only

A first chance exception of type 'System.Resources.MissingManifestResourceException'.

Viewing exception details, the system was requesting MyAssembly.g.resources

Hope this might be of help to someone else.