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Fix Form with StartPosition=CenterParent and WindowState=Maximized opening on wrong monitor #14156

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Fix Form with StartPosition=CenterParent and WindowState=Maximized opening on wrong monitor #14156

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Fix Form with StartPosition=CenterParent and WindowState=Maximized op…
LeafShi1 Dec 22, 2025
4347fc0
Delete duplicate code
LeafShi1 Dec 22, 2025
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9 changes: 7 additions & 2 deletions src/System.Windows.Forms/System/Windows/Forms/Form.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5731,6 +5731,13 @@ public DialogResult ShowDialog(IWin32Window? owner)
// to CreateControl().
_dialogResult = DialogResult.None;

// Set dialog owner before CreateControl() so that
// FillInCreateParamsStartPosition can access it when positioning maximized forms
if (owner is not null && !ownerHwnd.IsNull)
{
Properties.AddOrRemoveValue(s_propDialogOwner, owner);
}

// If "this" is an MDI parent then the window gets activated,
// causing GetActiveWindow to return "this.handle"... to prevent setting
// the owner of this to this, we must create the control AFTER calling
Expand All @@ -5750,8 +5757,6 @@ public DialogResult ShowDialog(IWin32Window? owner)
// So, it is necessary to not set the owner before creating the handle. Otherwise,
// the window may never receive Dpi changed event even if its parent has different Dpi.
// Users at runtime, has to move the window between the screens to get the Dpi changed events triggered.

Properties.AddOrRemoveValue(s_propDialogOwner, owner);
if (owner is Form form && owner != oldOwner)
{
Owner = form;
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