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[release-notes] Windows Forms in .NET 11 Preview 4 #10400

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[release-notes] Windows Forms in .NET 11 Preview 4 (initial)
danroth27 Apr 29, 2026
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[release-notes] Author winforms.md content
danroth27 Apr 30, 2026
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36 changes: 36 additions & 0 deletions release-notes/11.0/preview/preview4/winforms.md
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# Windows Forms in .NET 11 Preview 4 - Release Notes

.NET 11 Preview 4 does not introduce new Windows Forms feature additions. The
notable user-facing change in this preview is a clipboard regression fix.

- [Bug fixes](#bug-fixes)

<!-- Filtered features (significant engineering work, but too niche for release notes):
- Add documentation and in-code awareness for shared WinForms/WPF clipboard/OLE infrastructure (dotnet/winforms #14306). Repo-internal contributor docs only; no behavior change.
- Adding NuGet package for Microsoft.Private.Windows.Core assembly (dotnet/winforms #14429). Internal transport package for VS/WPF consumption; not a public surface.
- Updating TFM for .NET Framework assembly from net472 to net481 (dotnet/winforms #14450). Build/infra-only change to internal projects.
- Pin System.Formats.Nrbf and its transitive dependencies to 10.0.4 release for .NET Framework (dotnet/winforms #14487). Dependency pin for .NET Framework build; no app-visible change.
- Fix WinformsControlTest exit when clicking Column2 header (dotnet/winforms #14477). Bug in the in-repo test/sample app, not the product.
- Multiple "[main] Source code updates from dotnet/dotnet" PRs (#14409, #14419, #14426, #14431, #14432, #14433, #14437, #14443, #14444, #14446, #14456, #14464, #14470, #14476, #14479). VMR sync noise.
- Repo Copilot/skill workflow updates (#14428, #14451, #14480). Repo automation only.
-->

## Bug fixes

- **System.Windows.Forms.Clipboard / DataObject**
- `Clipboard.GetDataObject().GetImage()` once again returns bitmap images
placed on the clipboard. After the typed/NRBF clipboard pipeline shipped
in .NET 10, bitmaps were stored in the typed data store, but
`DataObject.GetImage` only read from the legacy `GetData` store and
returned `null`. `DataObject.GetImage` now first tries the typed pipeline
via `TryGetData<Image>(DataFormats.Bitmap, autoConvert: true, ...)` and
falls back to the legacy path, matching the behavior of
`Clipboard.GetImage()`
([dotnet/winforms #14427](https://github.com/dotnet/winforms/pull/14427),
[dotnet/winforms #14423](https://github.com/dotnet/winforms/issues/14423)).

```csharp
// Round-trips again on .NET 11 Preview 4
Clipboard.SetImage(bitmap);
Image? image = Clipboard.GetDataObject()?.GetImage();
```
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