I don't think this will work, I'm not 100% certain but I think loading types is lazy, so it already will only load them at the point they are used. However if they are used then it typically will be in the form/control constructor (in the generated designer code part), so throwing an exception will mean you have that exception being thrown in your third party form/control constructor. That probably is not helpful and just changes the error you are getting?

Libraries that are not so much in development anymore.

I suspect if these are WinForms based libraries you'll have a hard time to get this working properly in .NET Core, there are subtile changes like the default font being different which mean that it often needs code adjustments to work well on .NET Core.

It would have been nice to be able to just run Desktop Framework WinForms code on .NET Core but the decision was made against that and I don't think it can be changed at this point.

In general you are right and this will not work -- but all my 3rd party libraries are using the "new" controls that have replaced the deprecated ones -- it is just that they kept supporting the deprecated ones with code like "if (this.ContextMenuStrip != null) { ..use new control...} else if (this.ContextMenu != null) { ..keep it backwards compatible...}. Now if ContextMenu just worked and returned null as I do not use it, it would have worked in runtime -- now it gives "cannot find/load type ContextMenu.

Making it hard to upgrade existing winforms applications to .NET5 is a mistake in my opinion. (it all worked nicely in .NET Core 3.0, why change that?)

these controls already were removed in .NET Core 3.1 (the LTS version of 3.0 - .NET Core 3.0 is already out of support)

Exactly, that is why I cannot use .NET Core 3.0, not shipping something that is out of support to my customers.

@msneijders have you tried creating dummy classes for these deprecated types in your assembly, and type-forwarding them to the Windows Forms assembly?

@teo-tsirpanis I did not try this yet, but I will soon, thank you for this suggestion.

Type-forwarding does not seem like a workaround -- I think forwarding needs to be done from the System.Windows.Forms assembly.

Hmm, doesn't it work the other way around? There's an attribute named TypeForwardedFrom which is applied to the declared type, in contrast with the TypeForwardedToAttribute which is applied to the receiving assembly.

It is written like this: [TypeForwardedFrom("System.Windows.Forms")].

@msneijders said he doesn't himself use these legacy controls in application code. He uses an old control library wich supports both the legacy and the new controls, but the legacy control code path will never be executed.

We don't care about the compiler recognizing them. All we want is a runtime trick to not crash the loader because of a couple of classes were not found.

We also experienced this. Added dotnet/runtime#41088 , but ...
...basically we have accepted that moving to net5+ means replacing some 3rd party altogether.

It is frustrating however that net core 3.0 had the types ...

@LeafShi1 let's get this on your team's radar, so that we can help customers do their migrations.
@Tanya-Solyanik FYI, per discussion with @JeremyKuhne

@LeafShi1 @Epica3055 @SimonZhao888 @ricardobossan, here are the steps to start with -

1. generate public API surface for NETFX 481 System.Windows.Forms.dd and for NET9 SystemWindows.Froms.dll and find public or protected APIs that we had removed, not only the classes but also class members. We have a list of removed controls here - https://learn.microsoft.com/dotnet/core/compatibility/winforms#removed-controls but it might be incomplete.
2. create a repro application based on the description in this issue, a .NET9 exe that references a NETFX481 dll that uses deleted controls.
3. add empty control and public members declarations to NET9, copying them from release/3.0 branch. All methods would throw a PlatformNotSupportedException
4. all properties should be hidden from intellisense, property browser and serializers. This is achieved by setting browsable attributes to false/hide to restored members in the existing classes -

• https://learn.microsoft.com/dotnet/api/system.componentmodel.browsableattribute?view=net-8.0
• https://learn.microsoft.com/dotnet/api/system.componentmodel.editorbrowsableattribute?view=net-8.0
• https://learn.microsoft.com/dotnet/api/system.componentmodel.designerserializationvisibilityattribute?view=net-8.0
  and [EditorBrowsable(EditorBrowsableState.Never)] to whole restored classes

5. Set ObsoleteAttribute, and an error message on all restored types and APIs that were re-added to the existing types. See eff830b for details.

@Tanya-Solyanik
I just want someone to make sure that I will still be able to use the NuGet package winforms-datavisualization from https://github.com/kirsan31/winforms-datavisualization which replaced the .NET Framework datavisualization control in applications that were moved to .Net Core.

Have all the obsolete controls been open sourced?

@paul1956 - DataVisualization is out of scope of this item. This item is only about public APIs that were removed from System.Windows.Forms.dll

We have done the migration by reimplementing missing functionality.
Winforms gave us the worst issues so solving this is Nice.
but the re is still the life cycle issue of LTS being too short on .NET. Even If we developers love the pace of. NET, customers cant keep up. There is a need for an "eternal" Net 10 (just like Net48) for some customers to swap out Net48 and just ENJOY Windows Update security patching.

@JensNordenbro I totally understand what you're saying here! Note that you can enable .NET updates in Microsoft Update so that servicing updates are automatically installed. We don't have an automatic upgrade between major versions, however, and you're right about the 3-year LTS cycle. We do this to help facilitate our customers keeping updated with both new functionality and the latest perf and security updates.

/cc: @jamshedd

Yes @merriemcgaw, I know!

Maybe it is enough, however if you want to grab the late runners I think introducing a new tier of LTS of 5 years or something is needed.

Polyfilling api:s might not be the real problem. - It helps though.

1. generate public API surface for NETFX 481 System.Windows.Forms.dd and for NET9 SystemWindows.Froms.dll and find public or protected APIs that we had removed

1. System.Windows.Forms.StatusBar
   override System.Windows.Forms.StatusBar.BackColor.get -> System.Drawing.Color
   override System.Windows.Forms.StatusBar.BackColor.set -> void
   override System.Windows.Forms.StatusBar.BackgroundImage.get -> System.Drawing.Image
   override System.Windows.Forms.StatusBar.BackgroundImage.set -> void
   override System.Windows.Forms.StatusBar.BackgroundImageLayout.get -> System.Windows.Forms.ImageLayout
   override System.Windows.Forms.StatusBar.BackgroundImageLayout.set -> void
   override System.Windows.Forms.StatusBar.CreateHandle() -> void
   override System.Windows.Forms.StatusBar.CreateParams.get -> System.Windows.Forms.CreateParams
   override System.Windows.Forms.StatusBar.DefaultImeMode.get -> System.Windows.Forms.ImeMode
   override System.Windows.Forms.StatusBar.DefaultSize.get -> System.Drawing.Size
   override System.Windows.Forms.StatusBar.Dispose(bool disposing) -> void
   override System.Windows.Forms.StatusBar.Dock.get -> System.Windows.Forms.DockStyle
   override System.Windows.Forms.StatusBar.Dock.set -> void
   override System.Windows.Forms.StatusBar.DoubleBuffered.get -> bool
   override System.Windows.Forms.StatusBar.DoubleBuffered.set -> void
   override System.Windows.Forms.StatusBar.Font.get -> System.Drawing.Font
   override System.Windows.Forms.StatusBar.Font.set -> void
   override System.Windows.Forms.StatusBar.ForeColor.get -> System.Drawing.Color
   override System.Windows.Forms.StatusBar.ForeColor.set -> void
   override System.Windows.Forms.StatusBar.OnHandleCreated(System.EventArgs e) -> void
   override System.Windows.Forms.StatusBar.OnHandleDestroyed(System.EventArgs e) -> void
   override System.Windows.Forms.StatusBar.OnLayout(System.Windows.Forms.LayoutEventArgs levent) -> void
   override System.Windows.Forms.StatusBar.OnMouseDown(System.Windows.Forms.MouseEventArgs e) -> void
   override System.Windows.Forms.StatusBar.OnResize(System.EventArgs e) -> void
   override System.Windows.Forms.StatusBar.Text.get -> string
   override System.Windows.Forms.StatusBar.Text.set -> void
   override System.Windows.Forms.StatusBar.ToString() -> string
   override System.Windows.Forms.StatusBar.WndProc(ref System.Windows.Forms.Message m) -> void
   override System.Windows.Forms.StatusBarPanel.Dispose(bool disposing) -> void
   override System.Windows.Forms.StatusBarPanel.ToString() -> string
   System.Windows.Forms.StatusBar.BackColorChanged -> System.EventHandler
   System.Windows.Forms.StatusBar.BackgroundImageChanged -> System.EventHandler
   System.Windows.Forms.StatusBar.BackgroundImageLayoutChanged -> System.EventHandler
   System.Windows.Forms.StatusBar.DrawItem -> System.Windows.Forms.StatusBarDrawItemEventHandler
   System.Windows.Forms.StatusBar.ForeColorChanged -> System.EventHandler
   System.Windows.Forms.StatusBar.ImeMode.get -> System.Windows.Forms.ImeMode
   System.Windows.Forms.StatusBar.ImeMode.set -> void
   System.Windows.Forms.StatusBar.ImeModeChanged -> System.EventHandler
   System.Windows.Forms.StatusBar.Paint -> System.Windows.Forms.PaintEventHandler
   System.Windows.Forms.StatusBar.PanelClick -> System.Windows.Forms.StatusBarPanelClickEventHandler
   System.Windows.Forms.StatusBar.Panels.get -> System.Windows.Forms.StatusBar.StatusBarPanelCollection
   System.Windows.Forms.StatusBar.ShowPanels.get -> bool
   System.Windows.Forms.StatusBar.ShowPanels.set -> void
   System.Windows.Forms.StatusBar.SizingGrip.get -> bool
   System.Windows.Forms.StatusBar.SizingGrip.set -> void
   System.Windows.Forms.StatusBar.StatusBar() -> void
   System.Windows.Forms.StatusBar.TabStop.get -> bool
   System.Windows.Forms.StatusBar.TabStop.set -> void
   virtual System.Windows.Forms.StatusBar.OnDrawItem(System.Windows.Forms.StatusBarDrawItemEventArgs sbdievent) -> void
   virtual System.Windows.Forms.StatusBar.OnPanelClick(System.Windows.Forms.StatusBarPanelClickEventArgs e) -> void

2. System.Windows.Forms.StatusBar.StatusBarPanelCollection
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.Contains(System.Windows.Forms.StatusBarPanel panel) -> bool
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.Count.get -> int
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.GetEnumerator() -> System.Collections.IEnumerator
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.IndexOf(System.Windows.Forms.StatusBarPanel panel) -> int
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.IsReadOnly.get -> bool
   System.Windows.Forms.StatusBar.StatusBarPanelCollection.StatusBarPanelCollection(System.Windows.Forms.StatusBar owner) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.Add(string text) -> System.Windows.Forms.StatusBarPanel
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.Add(System.Windows.Forms.StatusBarPanel value) -> int
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.AddRange(System.Windows.Forms.StatusBarPanel[] panels) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.Clear() -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.ContainsKey(string key) -> bool
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.IndexOfKey(string key) -> int
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.Insert(int index, System.Windows.Forms.StatusBarPanel value) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.Remove(System.Windows.Forms.StatusBarPanel value) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.RemoveAt(int index) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.RemoveByKey(string key) -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.this[int index].get -> System.Windows.Forms.StatusBarPanel
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.this[int index].set -> void
   virtual System.Windows.Forms.StatusBar.StatusBarPanelCollection.this[string key].get -> System.Windows.Forms.StatusBarPanel

3. System.Windows.Forms.StatusBarDrawItemEventArgs
   System.Windows.Forms.StatusBarDrawItemEventArgs.Panel.get -> System.Windows.Forms.StatusBarPanel
   System.Windows.Forms.StatusBarDrawItemEventArgs.StatusBarDrawItemEventArgs(System.Drawing.Graphics g, System.Drawing.Font font, System.Drawing.Rectangle r, int itemId, System.Windows.Forms.DrawItemState itemState, System.Windows.Forms.StatusBarPanel panel, System.Drawing.Color foreColor, System.Drawing.Color backColor) -> void
   System.Windows.Forms.StatusBarDrawItemEventArgs.StatusBarDrawItemEventArgs(System.Drawing.Graphics g, System.Drawing.Font font, System.Drawing.Rectangle r, int itemId, System.Windows.Forms.DrawItemState itemState, System.Windows.Forms.StatusBarPanel panel) -> void

4. System.Windows.Forms.StatusBarPanel
   System.Windows.Forms.StatusBarPanel.Alignment.get -> System.Windows.Forms.HorizontalAlignment
   System.Windows.Forms.StatusBarPanel.Alignment.set -> void
   System.Windows.Forms.StatusBarPanel.AutoSize.get -> System.Windows.Forms.StatusBarPanelAutoSize
   System.Windows.Forms.StatusBarPanel.AutoSize.set -> void
   System.Windows.Forms.StatusBarPanel.BeginInit() -> void
   System.Windows.Forms.StatusBarPanel.BorderStyle.get -> System.Windows.Forms.StatusBarPanelBorderStyle
   System.Windows.Forms.StatusBarPanel.BorderStyle.set -> void
   System.Windows.Forms.StatusBarPanel.EndInit() -> void
   System.Windows.Forms.StatusBarPanel.Icon.get -> System.Drawing.Icon
   System.Windows.Forms.StatusBarPanel.Icon.set -> void
   System.Windows.Forms.StatusBarPanel.MinWidth.get -> int
   System.Windows.Forms.StatusBarPanel.MinWidth.set -> void
   System.Windows.Forms.StatusBarPanel.Name.get -> string
   System.Windows.Forms.StatusBarPanel.Name.set -> void
   System.Windows.Forms.StatusBarPanel.Parent.get -> System.Windows.Forms.StatusBar
   System.Windows.Forms.StatusBarPanel.StatusBarPanel() -> void
   System.Windows.Forms.StatusBarPanel.Style.get -> System.Windows.Forms.StatusBarPanelStyle
   System.Windows.Forms.StatusBarPanel.Style.set -> void
   System.Windows.Forms.StatusBarPanel.Tag.get -> object
   System.Windows.Forms.StatusBarPanel.Tag.set -> void
   System.Windows.Forms.StatusBarPanel.Text.get -> string
   System.Windows.Forms.StatusBarPanel.Text.set -> void
   System.Windows.Forms.StatusBarPanel.ToolTipText.get -> string
   System.Windows.Forms.StatusBarPanel.ToolTipText.set -> void
   System.Windows.Forms.StatusBarPanel.Width.get -> int
   System.Windows.Forms.StatusBarPanel.Width.set -> void

5. System.Windows.Forms.StatusBarPanelAutoSize
   System.Windows.Forms.StatusBarPanelAutoSize.Contents = 3 -> System.Windows.Forms.StatusBarPanelAutoSize
   System.Windows.Forms.StatusBarPanelAutoSize.None = 1 -> System.Windows.Forms.StatusBarPanelAutoSize
   System.Windows.Forms.StatusBarPanelAutoSize.Spring = 2 -> System.Windows.Forms.StatusBarPanelAutoSize

6. System.Windows.Forms.StatusBarPanelBorderStyle
   System.Windows.Forms.StatusBarPanelBorderStyle.None = 1 -> System.Windows.Forms.StatusBarPanelBorderStyle
   System.Windows.Forms.StatusBarPanelBorderStyle.Raised = 2 -> System.Windows.Forms.StatusBarPanelBorderStyle
   System.Windows.Forms.StatusBarPanelBorderStyle.Sunken = 3 -> System.Windows.Forms.StatusBarPanelBorderStyle

7. System.Windows.Forms.StatusBarPanelClickEventArgs
   System.Windows.Forms.StatusBarPanelClickEventArgs.StatusBarPanel.get -> System.Windows.Forms.StatusBarPanel
   System.Windows.Forms.StatusBarPanelClickEventArgs.StatusBarPanelClickEventArgs(System.Windows.Forms.StatusBarPanel statusBarPanel, System.Windows.Forms.MouseButtons button, int clicks, int x, int y) -> void
   System.Windows.Forms.StatusBarPanelClickEventHandler

8. System.Windows.Forms.StatusBarPanelStyle
   System.Windows.Forms.StatusBarPanelStyle.OwnerDraw = 2 -> System.Windows.Forms.StatusBarPanelStyle
   System.Windows.Forms.StatusBarPanelStyle.Text = 1 -> System.Windows.Forms.StatusBarPanelStyle

9. System.Windows.Forms.IDataGridEditingService
   System.Windows.Forms.IDataGridEditingService.BeginEdit(System.Windows.Forms.DataGridColumnStyle gridColumn, int rowNumber) -> bool
   System.Windows.Forms.IDataGridEditingService.EndEdit(System.Windows.Forms.DataGridColumnStyle gridColumn, int rowNumber, bool shouldAbort) -> bool

I don't think thats complete? I remember the discussion of removing the old menu APIs. So unless I'm misunderstanding what you're trying to do, shouldn't those appear on the list too?

You don't need to go far.

• https://learn.microsoft.com/dotnet/core/compatibility/winforms#removed-controls
• fix 2091 Remove deprecated controls #2157
• Remove deprecated API #2798