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2D Introduce the new API InitializeControl on Control by KlausLoeffelmann · Pull Request #13551 · dotnet/winforms · GitHub
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Introduce the new API InitializeControl on Control #13551

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Introduce the new API InitializeControl on Control #13551

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8250653
Introduce InitializeControl and refactor for DarkMode and InitialDPI …
KlausLoeffelmann Jun 3, 2025
549e268
Implement DarkMode applying with [Re]CreateHandle.
KlausLoeffelmann Jun 8, 2025
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13 changes: 0 additions & 13 deletions src/System.Windows.Forms/PublicAPI.Shipped.txt
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@@ -1,23 +1,10 @@
#nullable enable
[WFO5001]static System.Windows.Forms.Application.SetColorMode(System.Windows.Forms.SystemColorMode systemColorMode) -> void
[WFO5001]System.Windows.Forms.ControlStyles.ApplyThemingImplicitly = 524288 -> System.Windows.Forms.ControlStyles
[WFO5001]System.Windows.Forms.Form.FormBorderColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCaptionBackColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCaptionTextColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCornerPreferenceChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.Default = 0 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.DoNotRound = 1 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.Round = 2 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.RoundSmall = 3 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.SystemColorMode
[WFO5001]System.Windows.Forms.SystemColorMode.Classic = 0 -> System.Windows.Forms.SystemColorMode
[WFO5001]System.Windows.Forms.SystemColorMode.Dark = 2 -> System.Windows.Forms.SystemColorMode
[WFO5001]System.Windows.Forms.SystemColorMode.System = 1 -> System.Windows.Forms.SystemColorMode
[WFO5001]virtual System.Windows.Forms.Form.OnFormBorderColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCaptionBackColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCaptionTextColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCornerPreferenceChanged(System.EventArgs! e) -> void
[WFO5002]static System.Windows.Forms.TaskDialog.ShowDialogAsync(nint hwndOwner, System.Windows.Forms.TaskDialogPage! page, System.Windows.Forms.TaskDialogStartupLocation startupLocation = System.Windows.Forms.TaskDialogStartupLocation.CenterOwner) -> System.Threading.Tasks.Task<System.Windows.Forms.TaskDialogButton!>!
[WFO5002]static System.Windows.Forms.TaskDialog.ShowDialogAsync(System.Windows.Forms.IWin32Window! owner, System.Windows.Forms.TaskDialogPage! page, System.Windows.Forms.TaskDialogStartupLocation startupLocation = System.Windows.Forms.TaskDialogStartupLocation.CenterOwner) -> System.Threading.Tasks.Task<System.Windows.Forms.TaskDialogButton!>!
[WFO5002]static System.Windows.Forms.TaskDialog.ShowDialogAsync(System.Windows.Forms.TaskDialogPage! page, System.Windows.Forms.TaskDialogStartupLocation startupLocation = System.Windows.Forms.TaskDialogStartupLocation.CenterScreen) -> System.Threading.Tasks.Task<System.Windows.Forms.TaskDialogButton!>!
Expand Down
30 changes: 30 additions & 0 deletions src/System.Windows.Forms/PublicAPI.Unshipped.txt
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Expand Up @@ -4,3 +4,33 @@ System.Windows.Forms.ScreenCaptureMode
System.Windows.Forms.ScreenCaptureMode.Allow = 0 -> System.Windows.Forms.ScreenCaptureMode
System.Windows.Forms.ScreenCaptureMode.HideContent = 1 -> System.Windows.Forms.ScreenCaptureMode
System.Windows.Forms.ScreenCaptureMode.HideWindow = 2 -> System.Windows.Forms.ScreenCaptureMode
override System.Windows.Forms.ButtonBase.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.CheckBox.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.DataGridView.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.Label.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.ListBox.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.MonthCalendar.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.PictureBox.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.ProgressBar.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.RadioButton.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.ScrollableControl.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.ScrollBar.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.Splitter.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.TabControl.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.TabPage.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.TrackBar.InitializeControl(int deviceDpi) -> void
override System.Windows.Forms.TreeView.InitializeControl(int deviceDpi) -> void
virtual System.Windows.Forms.Control.InitializeControl(int deviceDpi) -> void
[WFO5001]System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.Default = 0 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.DoNotRound = 1 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.Round = 2 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.FormCornerPreference.RoundSmall = 3 -> System.Windows.Forms.FormCornerPreference
[WFO5001]System.Windows.Forms.Form.FormBorderColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCaptionBackColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCaptionTextColorChanged -> System.EventHandler?
[WFO5001]System.Windows.Forms.Form.FormCornerPreferenceChanged -> System.EventHandler?
[WFO5001]virtual System.Windows.Forms.Form.OnFormBorderColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCaptionBackColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCaptionTextColorChanged(System.EventArgs! e) -> void
[WFO5001]virtual System.Windows.Forms.Form.OnFormCornerPreferenceChanged(System.EventArgs! e) -> void
118 changes: 95 additions & 23 deletions src/System.Windows.Forms/System/Windows/Forms/Control.cs
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Expand Up @@ -309,6 +309,7 @@ internal Control(bool autoInstallSyncContext) : base()

// Initialize Dpi to the value on the primary screen, we will have the correct value when the Handle is created.
_deviceDpi = _oldDeviceDpi = ScaleHelper.InitialSystemDpi;

_window = new ControlNativeWindow(this);
RequiredScalingEnabled = true;
RequiredScaling = BoundsSpecified.All;
Expand All @@ -326,16 +327,21 @@ internal Control(bool autoInstallSyncContext) : base()
| ControlStyles.Selectable,
true);

// Allows inheriting controls to initialize their control-specific state, as well as
// perform DPI-depending initialization of fields before the constructor code of the
// respective (inheriting) control has a chance to run.
// At this point, the control is not yet created, but every necessary state as well as
// the base class properties are in place, because they have been initialized by the
// static ctor of Control, which is called before all other instance constructors.
InitializeControl(_deviceDpi);

// We baked the "default default" margin and min size into CommonProperties
// so that in the common case the PropertyStore would be empty. If, however,
// someone overrides these Default* methods, we need to write the default
// value into the PropertyStore in the ctor.

// Changing the order of property accesses here can break existing code as these are all virtual properties.
// Try to keep observable state for Control unchanged in this constructor to avoid nasty subtle bugs.

InitializeConstantsForInitialDpi(_deviceDpi);

if (DefaultMargin != CommonProperties.DefaultMargin)
{
Margin = DefaultMargin;
Expand Down Expand Up @@ -389,7 +395,8 @@ public Control(string? text) : this(null, text)
//github.com/ <summary>
//github.com/ Initializes a new instance of the <see cref="Control"/> class.
//github.com/ </summary>
public Control(string? text, int left, int top, int width, int height) : this(null, text, left, top, width, height)
public Control(string? text, int left, int top, int width, int height)
: this(null, text, left, top, width, height)
{
}

Expand All @@ -411,6 +418,63 @@ public Control(Control? parent, string? text, int left, int top, int width, int
Size = new Size(width, height);
}

//github.com/ <summary>
//github.com/ Provides inheriting controls a dedicated early-initialization hook that is guaranteed to run
//github.com/ <i>before</i> <see cref="CreateParams"/> is called by any base class constructor.
//github.com/ This method enables derived controls to set styles, flags, or perform other setup that must
//github.com/ occur prior to any base class logic that depends on such initialization.
//github.com/ </summary>
//github.com/ <remarks>
//github.com/ <para>
//github.com/ In WinForms, the constructor call chain for controls can result in base class constructors
//github.com/ invoking methods such as <see cref="CreateParams"/> or other initialization logic
//github.com/ <b>before</b> the derived class's constructor body executes. This makes it impossible for
//github.com/ the derived class to perform certain setup in time using only its constructor.
//github.com/ </para>
//github.com/ <para>
//github.com/ For example, consider the following inheritance and call chain:
//github.com/ </para>
//github.com/ <code>
//github.com/ public class MyButton : Button
//github.com/ {
//github.com/ public MyButton()
//github.com/ {
//github.com/ // This code runs after Button's constructor, which may have already called CreateParams.
//github.com/ }
//github.com/
//github.com/ protected override void InitializeControl(int deviceDpi)
//github.com/ {
//github.com/ // This code runs before any base class calls to CreateParams or similar methods.
//github.com/ }
//github.com/ }
//github.com/
//github.com/ // Call chain:
//github.com/ new MyButton()
//github.com/ → Control..ctor()
//github.com/ → Control.InitializeControl (called in base constructor)
//github.com/ → ButtonBase.InitializeControl (called before CreateParams)
//github.com/ → Button.InitializeControl (called before CreateParams)
//github.com/ → MyButton.InitializeControl (called before CreateParams)
//github.com/ → Control.CreateParams (called in base constructor)
//github.com/ → ButtonBase.CreateParams (called before CreateParams)
//github.com/ → Button.CreateParams (called before CreateParams)
//github.com/ → MyButton.CreateParams (called before CreateParams)
//github.com/ → MyButton.CreateParams (called before CreateParams)
//github.com/ → ButtonBase..ctor()
//github.com/ → Button..ctor()
//github.com/ → MyButton..ctor()
//github.com/ </code>
//github.com/ <para>
//github.com/ By overriding <c>InitializeControl</c>, inheritors can ensure their initialization logic
//github.com/ runs at the correct time, even when base class constructors invoke methods that require
//github.com/ early setup.
//github.com/ </para>
//github.com/ </remarks>
//github.com/ <param name="deviceDpi">The DPI value for the control's device context.</param>
protected virtual void InitializeControl(int deviceDpi)
{
}

//github.com/ <summary>
//github.com/ Gets control Dpi awareness context value.
//github.com/ </summary>
Expand Down Expand Up @@ -7297,16 +7361,6 @@ protected virtual void OnHandleCreated(EventArgs e)
PInvoke.SetWindowText(this, _text);
}

#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
if (Application.IsDarkModeEnabled && GetStyle(ControlStyles.ApplyThemingImplicitly))
{
_ = PInvoke.SetWindowTheme(
hwnd: HWND,
pszSubAppName: $"{DarkModeIdentifier}_{ExplorerThemeIdentifier}",
pszSubIdList: null);
}
#pragma warning restore WFO5001

if (this is not ScrollableControl
&& !IsMirrored
&& GetExtendedState(ExtendedStates.SetScrollPosition)
Expand All @@ -7316,6 +7370,18 @@ protected virtual void OnHandleCreated(EventArgs e)
SetExtendedState(ExtendedStates.HaveInvoked, true);
SetExtendedState(ExtendedStates.SetScrollPosition, false);
}

#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
if (Application.IsDarkModeEnabled
&& GetStyle(ControlStyles.ApplyThemingImplicitly)
&& !RecreatingHandle)
{
_ = PInvoke.SetWindowTheme(
hwnd: HWND,
pszSubAppName: $"{DarkModeIdentifier}_{ExplorerThemeIdentifier}",
pszSubIdList: null);
}
#pragma warning restore WFO5001
}

((EventHandler?)Events[s_handleCreatedEvent])?.Invoke(this, e);
Expand Down Expand Up @@ -8035,15 +8101,6 @@ protected virtual void OnValidated(EventArgs e)
((EventHandler?)Events[s_validatedEvent])?.Invoke(this, e);
}

//github.com/ <summary>
//github.com/ This is called in the <see cref="Control"/> constructor before calculating the initial <see cref="Size"/>.
//github.com/ This gives a chance to initialize fields that will be used in calls to sizing related virtuals such as
//github.com/ <see cref="DefaultSize"/>, etc. The real size cannot be calculated until the handle is created as Windows
//github.com/ can have their own DPI setting. When the handle is created, <see cref="RescaleConstantsForDpi(int, int)"/>
//github.com/ is called.
//github.com/ </summary>
private protected virtual void InitializeConstantsForInitialDpi(int initialDpi) { }

//github.com/ <summary>
//github.com/ Invoked when the control handle is created and right before the top level parent control receives a
//github.com/ WM_DPICHANGED message.
Expand Down Expand Up @@ -9268,6 +9325,21 @@ internal virtual void RecreateHandleCore()
}
}

// Note that we need to take DarkMode theming into account at a different point in time
// than when we create the handle for the first time. The reason is that recreating the handle
// usually also recreates the handles of any child controls, and we want to
// ensure that the theming is applied to all child controls as well.
#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
if (Application.IsDarkModeEnabled
&& GetStyle(ControlStyles.ApplyThemingImplicitly))
{
_ = PInvoke.SetWindowTheme(
hwnd: HWND,
pszSubAppName: $"{DarkModeIdentifier}_{ExplorerThemeIdentifier}",
pszSubIdList: null);
}
#pragma warning restore WFO5001

// Restore control focus
if (focused)
{
Expand Down
32 changes: 32 additions & 0 deletions src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/Button.cs
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Expand Up @@ -146,6 +146,38 @@ public virtual DialogResult DialogResult
}
}

#pragma warning disable WFO5001
//github.com/ <summary>
//github.com/ Defines, whether the control is owner-drawn. Based on this,
//github.com/ the UserPaint flags get set, which in turn makes it later
//github.com/ a Win32 controls, which we wrap (OwnerDraw == false) or if we
//github.com/ draw ourselves. If the user wants to opt out of DarkMode, we cannot
//github.com/ force System-Painting for FlatStyle.Standard, so we need to know here
//github.com/ and now.
//github.com/ </summary>
private protected override bool OwnerDraw
{
get
{
if (Application.IsDarkModeEnabled
// The SystemRenderer cannot render images. So, we flip to our
// own DarkMode renderer, if we need to render images, except if
&& GetStyle(ControlStyles.ApplyThemingImplicitly)
// the user wants to opt out of implicit DarkMode rendering.
&& Image is null
// And this only counts for FlatStyle.Standard. For the rest,
// we're using specific renderers, which check themselves, if
// they need to apply Light- or DarkMode.
&& FlatStyle == FlatStyle.Standard)
{
return false;
}

return base.OwnerDraw;
}
}
#pragma warning restore WFO5001

internal override bool SupportsUiaProviders => true;

//github.com/ <summary>
Expand Down
17 changes: 12 additions & 5 deletions src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonBase.cs
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Expand Up @@ -78,14 +78,21 @@ protected ButtonBase()

SetStyle(ControlStyles.UserMouse | ControlStyles.UserPaint, OwnerDraw);

#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
SetStyle(ControlStyles.ApplyThemingImplicitly, true);
#pragma warning restore WFO5001

SetFlag(FlagUseMnemonic, true);
SetFlag(FlagShowToolTip, false);
}

#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
protected override void InitializeControl(int deviceDpi)
{
// Call the base classes, and let them setup their fields.
base.InitializeControl(deviceDpi);

// Opt into DarkMode.
SetStyle(ControlStyles.ApplyThemingImplicitly, true);
}
#pragma warning restore WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.

//github.com/ <summary>
//github.com/ Gets or sets a value indicating whether the ellipsis character (...) appears at the right edge of the control,
//github.com/ denoting that the control text extends beyond the specified length of the control.
Expand Down Expand Up @@ -617,7 +624,7 @@ internal virtual Rectangle OverChangeRectangle
}
}

internal bool OwnerDraw => FlatStyle != FlatStyle.System;
private protected virtual bool OwnerDraw => FlatStyle != FlatStyle.System;

bool? ICommandBindingTargetProvider.PreviousEnabledStatus { get; set; }

Expand Down
4 changes: 2 additions & 2 deletions src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/CheckBox.cs
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Expand Up @@ -49,6 +49,8 @@ public CheckBox() : base()
TextAlign = ContentAlignment.MiddleLeft;
}

protected override void InitializeControl(int deviceDpi) => ScaleConstants();

private bool AccObjDoDefaultAction { get; set; }

//github.com/ <summary>
Expand Down Expand Up @@ -256,8 +258,6 @@ protected override void RescaleConstantsForDpi(int deviceDpiOld, int deviceDpiNe
ScaleConstants();
}

private protected override void InitializeConstantsForInitialDpi(int initialDpi) => ScaleConstants();

private void ScaleConstants()
{
const int LogicalFlatSystemStylePaddingWidth = 25;
Expand Down
5 changes: 2 additions & 3 deletions src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/RadioButton.cs
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Expand Up @@ -233,9 +233,6 @@ protected override void RescaleConstantsForDpi(int deviceDpiOld, int deviceDpiNe
ScaleConstants();
}

private protected override void InitializeConstantsForInitialDpi(int initialDpi)
=> ScaleConstants();

private void ScaleConstants()
{
const int LogicalFlatSystemStylePaddingWidth = 24;
Expand All @@ -244,6 +241,8 @@ private void ScaleConstants()
_flatSystemStyleMinimumHeight = LogicalToDeviceUnits(LogicalFlatSystemStyleMinimumHeight);
}

protected override void InitializeControl(int deviceDpi) => ScaleConstants();

internal override Size GetPreferredSizeCore(Size proposedConstraints)
{
if (FlatStyle != FlatStyle.System)
Expand Down
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