Fix clipboard GetData documentation to reflect NotSupportedException instead of null

[Copilot]

Summary

Code examples incorrectly documented that Clipboard.GetData() returns null when BinaryFormatter is unavailable. The actual behavior returns a NotSupportedException instance. Additionally, the code examples were checking for null instead of validating the returned type.

Changes

• Updated C# and VB code comments in ObsoletePatterns.cs/vb to accurately reflect exception behavior
• Changed "returns null" → "returns a NotSupportedException instance" (4 comment lines total)
• Fixed conditional checks in C# from if (data != null) to if (data is Person person) using pattern matching
• Fixed conditional checks in VB from If data IsNot Nothing Then to If TypeOf data Is Person Then
• Updated VB cast from CType to DirectCast for better performance after type validation

Example

// Before:
// Later attempts to retrieve the data return null
object data = Clipboard.GetData("MyApp.Person");
if (data != null)
{
    Person person = (Person)data;
    Console.WriteLine($"Processing person: {person.Name}, Age: {person.Age}");
}

// After:
// Later attempts to retrieve the data return a NotSupportedException instance
object data = Clipboard.GetData("MyApp.Person");
if (data is Person person)
{
    Console.WriteLine($"Processing person: {person.Name}, Age: {person.Age}");
}

VB Example

' Before:
' Returns a NotSupportedException instance for a custom object type
If data IsNot Nothing Then
    Dim person As Person = CType(data, Person)
    Console.WriteLine($"Processing person: {person.Name}, Age: {person.Age}")
End If

' After:
' Returns a NotSupportedException instance for a custom object type
If TypeOf data Is Person Then
    Dim person As Person = DirectCast(data, Person)
    Console.WriteLine($"Processing person: {person.Name}, Age: {person.Age}")
End If

This aligns the code examples with the main article documentation, which correctly states that GetData() returns a NotSupportedException when BinaryFormatter is required but not enabled, and ensures the code properly validates the type before using the data.

Fixes #2146

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Some code examples still show null for Clipboard GetData when instead they return an exception</issue_title>
<issue_description>### Type of issue

Code doesn't work

Description

There was a behavior change from the time the article was written to when it was actually published. Some of the code examples still show, expect, or comment about null being returned when in fact it returns a NotSupportedException instance. These should be fixed.

Page URL

https://learn.microsoft.com/en-us/dotnet/desktop/winforms/migration/clipboard-dataobject-net10

Content source URL

https://github.com/dotnet/docs-desktop/blob/main/dotnet-desktop-guide/winforms/migration/clipboard-dataobject-net10.md

Document Version Independent Id

d7829387-6c41-1e77-8c93-113d49382167

Platform Id

54424045-aea6-3a25-8c01-9c53dc5840ca

Article author

@adegeo

Metadata

• ID: d7829387-6c41-1e77-8c93-113d49382167
• PlatformId: 54424045-aea6-3a25-8c01-9c53dc5840ca
• Service: dotnet-desktop
• Sub-service: winforms

Related Issues</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Some code examples still show null for Clipboard GetData when instead they return an exception #2146

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

[Copilot]

Pull Request Overview

This PR fixes documentation comments in code examples that incorrectly stated Clipboard.GetData() returns null when BinaryFormatter is unavailable. The actual behavior is that it returns a NotSupportedException instance.

• Updated 4 comment lines across C# and VB code example files
• Changes align with the main article documentation which correctly describes the exception return behavior
• All modifications are limited to comments only; no code logic was changed

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
dotnet-desktop-guide/winforms/migration/snippets/clipboard-dataobject-net10/net/csharp/ObsoletePatterns.cs	Updated 2 comments to reflect that GetData() returns a NotSupportedException instance instead of null
dotnet-desktop-guide/winforms/migration/snippets/clipboard-dataobject-net10/net/vb/ObsoletePatterns.vb	Updated 2 comments to reflect that GetData() returns a NotSupportedException instance instead of null

[adegeo]

@BillWagner This is ready