What's new for RC1 (#2122)

* Update compiler errors

* add code for darkmode

* Clean up wording related to .NET RC

* Minor

* Fix or

* Rewrite info

* Apply suggestions from code review

Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>

---------

Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>

Author: adegeo

dotnet-desktop-guide/winforms/compiler-messages/wfo5001.md

@@ -1,7 +1,7 @@
 ---
 title: Compiler Error WFO5001
 description: Learn more about compiler error WFO5001. 'ColorMode' is for evaluation purposes only and subject to change.
-ms.date: 03/04/2025
+ms.date: 09/09/2025
 ms.service: dotnet-desktop
 ms.update-cycle: 365-days
 f1_keywords:
@@ -16,12 +16,15 @@ helpviewer_keywords:
 
 > `System.Windows.Forms.Application.SetColorMode(System.Windows.Forms.SystemColorMode)` is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
 
--or-
+—or—
 
 > `System.Windows.Forms.SystemColorMode` is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
 
 The color mode feature is currently experimental and subject to change. This error is generated so that you understand the implications of writing code that sets the color mode of the Windows Forms project. The error must be suppressed to continue. For more information about this API, see [Dark mode](../whats-new/net90.md#dark-mode).
 
+> [!NOTE]
+> This compiler error no longer applies starting with .NET 10.
+
 ## Example
 
 The following sample generates WFO5001:
@@ -43,6 +46,10 @@ static class Program
 
 ## To correct this error
 
+Upgrade to .NET 10 or later, where this feature is no longer considered experimental.
+
+\- or -
+
 Suppress the error and enable access to the API by either of the following methods:
 
 - Set the severity of the rule in the _.editorConfig_ file.

dotnet-desktop-guide/winforms/compiler-messages/wfo5002.md

@@ -1,7 +1,7 @@
 ---
 title: Compiler Error WFO5002
 description: Learn more about compiler error WFO5002. Async is for evaluation purposes only and subject to change.
-ms.date: 03/04/2025
+ms.date: 09/10/2025
 ms.service: dotnet-desktop
 ms.update-cycle: 365-days
 f1_keywords:
@@ -24,6 +24,9 @@ This compiler error is generated when using any of the following methods:
 
 The Windows Forms asynchronous API is currently experimental and subject to change. This error is generated so that you understand the implications of writing code that uses these APIs. The error must be suppressed to continue. For more information about this API, see [Async forms](../whats-new/net90.md#async-forms).
 
+> [!NOTE]
+> This compiler error no longer applies starting with .NET 10.
+
 ## Example
 
 The following sample generates WFO5002:
@@ -38,6 +41,10 @@ private async void button1_Click(object sender, EventArgs e)
 
 ## To correct this error
 
+Upgrade to .NET 10 or later, where this feature is no longer considered experimental.
+
+—or—
+
 Suppress the error and enable access to the API by either of the following methods:
 
 - Set the severity of the rule in the _.editorConfig_ file.

dotnet-desktop-guide/winforms/whats-new/index.md

@@ -1,7 +1,7 @@
 ---
 title: What's new in Windows Forms
 description: Learn about what's new in Windows Forms. This article covers changes to Windows Forms since .NET 5 was released.
-ms.date: 03/17/2025
+ms.date: 09/09/2025
 ms.service: dotnet-desktop
 ms.update-cycle: 365-days
 ms.topic: conceptual
@@ -12,12 +12,18 @@ ai-usage: ai-assisted
 
 Each .NET release introduces a new version of Windows Forms (WinForms). This article gives you a summery of what's new in each release.
 
-## .NET 10 Preview
+## .NET 10 Release Candidate
 
-This section describes the main changes to WinForms for .NET 10 Preview.
+This section describes the main changes to WinForms for .NET 10 Release Candidate.
 
+- [Overview of Windows Forms on .NET 10](net100.md)
 - [Clipboard changes](net100.md#clipboard-changes)
+- [Async forms](net100.md#async-forms)
 - [Custom designer improvements](net100.md#custom-designer-improvements)
+- [Dark mode](net100.md#dark-mode)
+- [Accessibility](net100.md#accessibility)
+- [ScreenCaptureMode API](net100.md#screencapturemode-api)
+- [Analyzer improvements](net100.md#analyzer-improvements)
 
 ## .NET 9
 

dotnet-desktop-guide/winforms/whats-new/net100.md

@@ -1,23 +1,27 @@
 ---
-title: What's new in WinForms for .NET 10 Preview
-description: Learn about what's new in Windows Forms for .NET 10 Preview. New versions of Windows Forms are released yearly with .NET.
+title: What's new in WinForms for .NET 10 Release Candidate
+description: Learn about what's new in Windows Forms for .NET 10 Release Candidate. New versions of Windows Forms are released yearly with .NET.
 ms.topic: whats-new
-ms.date: 08/12/2025
+ms.date: 09/09/2025
 ms.service: dotnet-desktop
 ms.update-cycle: 365-days
+dev_langs:
+  - "csharp"
+  - "vb"
 #customer intent: As a developer, I want to know what's changed so that I can remain up-to-date.
 ---
 
-# What's new in Windows Forms for .NET 10 Preview
+# What's new in Windows Forms for .NET 10 Release Candidate
 
-This article provides a high-level overview about what's new with Windows Forms (WinForms) in .NET 10 Preview. For detailed information, see the [release announcements](#release-announcements).
+This article provides a high-level overview about what's new with Windows Forms (WinForms) in .NET 10 Release Candidate. For detailed information, see the [release announcements](#release-announcements).
 
-.NET 10 Preview 7 was released in August 2025.
+.NET 10 RC 1 was released in September 2025.
 
 ## Release announcements
 
 Each release announcement provides detailed information about Windows Forms changes for .NET 10:
 
+- [.NET 10 RC1](https://aka.ms/dotnet/10/rc1)
 - [.NET 10 Preview 7](https://aka.ms/dotnet/10/preview7)
 - [.NET 10 Preview 6](https://aka.ms/dotnet/10/preview6)
 - [.NET 10 Preview 5](https://aka.ms/dotnet/10/preview5)
@@ -32,6 +36,18 @@ Windows Forms is shipping new code for the clipboard API. The clipboard is redes
 
 .NET 9 obsoleted `BinaryFormatter`, which is used in some clipboard operations. These clipboard operations required you to opt in to compatibility package, or work around the operation. To ease the pain of moving away from `BinaryFormatter`, .NET 10 is obsoleting certain clipboard methods to indicate that they shouldn't be used. More methods are being added to help JSON serialization with clipboard data, circumventing the need for `BinaryFormatter`.
 
+## Async forms
+
+Windows Forms has fully integrated asynchronous forms support. Additionally, the async task now has a weak reference to the form, enabling responsive UIs when managing multiple windows.
+
+Windows Forms for .NET 9 introduced new methods to support displaying forms and dialogs asynchronously, but in an opt-in preview mode where you had to suppress [Compiler Error WFO5002](../compiler-messages/wfo5002.md) to use the feature. This compiler error is no longer triggered with .NET 10.
+
+The following APIs are no longer considered experimental:
+
+- <xref:System.Windows.Forms.Form.ShowAsync(System.Windows.Forms.IWin32Window)?displayProperty=nameWithType>
+- <xref:System.Windows.Forms.Form.ShowDialogAsync*?displayProperty=nameWithType>
+- <xref:System.Windows.Forms.TaskDialog.ShowDialogAsync*?displayProperty=nameWithType>
+
 ## Custom designer improvements
 
 Several <xref:System.Drawing.Design.UITypeEditor> types have been ported from .NET Framework, including `ToolStripCollectionEditor` and several editors related to the <xref:System.Windows.Forms.DataGridView> control. These editors are now discoverable by the <xref:System.Windows.Forms.PropertyGrid> and the Windows Forms Designer Actions panel.
@@ -40,18 +56,20 @@ SnapLines were fixed for custom designers.
 
 ## Dark mode
 
-Windows Forms for .NET 9 introduced preliminary dark mode visual styling, with the goal of completing implementation in .NET 10.
+Windows Forms has fully integrated dark mode support.
+
+Windows Forms for .NET 9 introduced preliminary dark mode visual styling, but in an opt-in preview mode where you had to suppress [Compiler Error WFO5001](../compiler-messages/wfo5001.md) to use the feature. This feature is no longer guarded behind this compiler error starting with .NET 10.
+
+The <xref:System.Windows.Forms.Application.SetColorMode(System.Windows.Forms.SystemColorMode)?displayProperty=nameWithType> API is no longer considered experimental.
 
-- `ListView` column headers are now working.
-- `StatusStrip` and `ToolStrip` render correctly.
-- Buttons with `FlatStyle` set to `Standard` also render correctly.
-- `ComboBox` and `RichTextBox` now render correctly when disabled.
+## Clarification on ControlStyles `ApplyThemingImplicitly` usage
 
-  However, `RichTextBox` has a rendering issue when it's disabled. If the `RichTextBox` has formatted content, only the first few visible lines appear correctly, and the formatting might not fully apply in the disabled state. To workaround this issue, set it to  read-only and manually disable selections.
+Controls follow color mode set for the application, dark or light. However, there might be a case where you're composing and drawing your own controls, yet use existing Win32 common controls, such as the scroll bar. These controls remain light colored unless you opt in to applying the theme before the `CreateParams` property is read. There also might be a case where you inherit a control that already follows the theming, and you want to opt out so that you fully control the drawing, such as with a Button.
 
-- `PropertyGrid` special buttons (ellipsis and drop-down) now render consistently in dark mode.
+Regardless of your use case, override the <xref:System.Windows.Forms.Control.CreateParams?displayProperty=nameWithType> property, and call [`SetStyle(ControlStyles.ApplyThemingImplicitly, true)`](xref:System.Windows.Forms.ControlStyles.ApplyThemingImplicitly?displayProperty=nameWithType) (opt-in) or [`SetStyle(ControlStyles.ApplyThemingImplicitly, false)`](xref:System.Windows.Forms.ControlStyles.ApplyThemingImplicitly?displayProperty=nameWithType) (opt-out) before the parameters are read from the base class. You **cannot** set this style in your constructor. The base constructor reads the `CreateParams` property before calling your constructor. The following code snippet shows how to opt in:
 
-- Many other fixes for color issues with dark mode.
+:::code language="csharp" source="./snippets/net100/csharp/CustomControl1.cs" id="CreateParams":::
+:::code language="vb" source="./snippets/net100/vb/CustomControl1.vb" id="CreateParams":::
 
 ## Bug fixes
 

dotnet-desktop-guide/winforms/whats-new/snippets/net100/csharp/CustomControl1.Designer.cs

@@ -0,0 +1,29 @@
+namespace WinFormsApp3;
+
+// <CreateParams>
+public partial class CustomControl1 : Control
+{
+    protected override CreateParams CreateParams
+    {
+        get
+        {
+            // Set this style BEFORE base.CreateParams is created and returned.
+            SetStyle(ControlStyles.ApplyThemingImplicitly, true);
+
+            CreateParams cp = base.CreateParams;
+            
+            // Other logic
+            return cp;
+        }
+    }
+
+    // Base class constructor is going to read CreateParams property
+    // before your constructor code runs.
+    public CustomControl1()  
+    {
+        // At this point, CreateParams property is already read, you
+        // can't set ApplyThemingImplicitly here.
+        InitializeComponent();
+    }
+}
+// </CreateParams>

dotnet-desktop-guide/winforms/whats-new/snippets/net100/csharp/CustomControl1.cs

@@ -0,0 +1,120 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!-- 
+    Microsoft ResX Schema 
+    
+    Version 2.0
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
+    associated with the data types.
+    
+    Example:
+    
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+                
+    There are any number of "resheader" rows that contain simple 
+    name/value pairs.
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
+    mimetype set.
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
+    extensible. For a given mimetype the value must be set accordingly:
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
+    read any of the formats listed below.
+    
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+    
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array 
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+</root>