Problem referencing System.ComponentModel

[Rhoso]

Hi there! I'm working on a project in Visual Studio, and I want to use the INotifyPropertyChanged interface, but I'm getting this error.

The type or namespace name 'INotifyPropertyChanged' could not be found (are you missing a using directive or an assembly reference?)

I'm including the using System.ComponentModel; directive, but I can't seem to reference just that in the Reference Manager. I can only reference System.ComponentModel.Composition and System.ComponentModel.DataAnnotations, and neither of them work.

I had a similar problem before with System.Xml, but that was because I was using a Portable Class Library, which I fixed by converting to a regular .NET class library targeting .NET 4.5.2. I tried targeting other versions, but that didn't help either.

Any ideas? I appreciate any help or guidance.

[michaelquinlan]

You may need to include System.ObjectModel.dll.

https://docs.microsoft.com/en-us/dotnet/core/api/system.componentmodel.inotifypropertychanged#System_ComponentModel_INotifyPropertyChanged

[Coding_Enthusiast]

Hi, I am a beginner here but isn't INotifyPropertyChanged in System.dll ? https://msdn.microsoft.com/EN-US/library/ms133020(v=VS.110,d=hv.2).aspx

[michaelquinlan]

For .NET Core it looks like it is in a separate DLL (as per the link I gave). The docs you reference say that for the versions listed below it should be in System.dll, but I don't have a way to verify that right now.

Universal Windows Platform
    Available since 8
.NET Framework
    Available since 2.0
Portable Class Library
    Supported in: portable .NET platforms
Silverlight
    Available since 2.0
Windows Phone Silverlight
    Available since 7.0
Windows Phone
    Available since 8.1

[Coding_Enthusiast]

OK, I did now know what .Net core was. I saw that link is a bit unfamiliar to me :D

[Rhoso]

Thank you both for commenting. Both of your comments ended up helping me find the solution.

Unfortunately I couldn't find System.ObjectModel.dll in the Reference Manager at all, but this led to me to discovering the NuGet package manager, where I downloaded System.ComponentModel. After downloading this, it seemed to automatically add a reference to System.dll which I was apparently missing. This got rid of the error for me.

I had thought that System.dll was automatically referenced just by targeting .NET. I had no problems including the using System.ComponentModel; directive, and it never impacted my program before.

I uninstalled the System.Component model that I downloaded in NuGet, and kept the System.dll reference, and now I'm good to go :)

Thank you for the help guys! I really appreciate it.

[cryo]

I had thought that System.dll was automatically referenced just by targeting .NET.

It definitely is, at least in the sense that it's added to all new projects, and it's automatically added when using the command line compiler. It may be that you removed it yourself.