[WinForms] Editing the DialogResult of the form in the button click event was ignored. (#18025)

Fixes #12022

2 files changed, 10 insertions, 6 deletions

diff --git a/mcs/class/System.Windows.Forms/System.Windows.Forms/Button.cs b/mcs/class/System.Windows.Forms/System.Windows.Forms/Button.cs
index 829c55012f0..fee7fb5d799 100644
--- a/mcs/class/System.Windows.Forms/System.Windows.Forms/Button.cs
+++ b/mcs/class/System.Windows.Forms/System.Windows.Forms/Button.cs
@@ -92,14 +92,16 @@ namespace System.Windows.Forms {
 		#region	Protected Methods
 		protected override void OnClick (EventArgs e)
 		{
-			if (dialog_result != DialogResult.None) {
-				Form p = FindForm ();
-
-				if (p != null)
+			Form p = FindForm ();
+			if (p != null) {
+				p.dialog_result_changed = false; // manages the case where the DialogResult of the form is overriden in the button click event.
+				base.OnClick (e);
+				if (dialog_result != DialogResult.None && !p.dialog_result_changed) {
 					p.DialogResult = dialog_result;
+				}
+			} else {
+				base.OnClick (e);
 			}
-			
-			base.OnClick (e);
 		}
 
 		protected override void OnFontChanged (EventArgs e)
diff --git a/mcs/class/System.Windows.Forms/System.Windows.Forms/Form.cs b/mcs/class/System.Windows.Forms/System.Windows.Forms/Form.cs
index 329736ffb81..73dff86a6a7 100644
--- a/mcs/class/System.Windows.Forms/System.Windows.Forms/Form.cs
+++ b/mcs/class/System.Windows.Forms/System.Windows.Forms/Form.cs
@@ -102,6 +102,7 @@ namespace System.Windows.Forms {
 		private bool			autoscale_base_size_set;
 		internal ArrayList disabled_by_showdialog = new ArrayList();
 		internal static ArrayList modal_dialogs = new ArrayList();
+		internal bool 			dialog_result_changed;
 		#endregion	// Local Variables
 
 		#region Private & Internal Methods
@@ -637,6 +638,7 @@ namespace System.Windows.Forms {
 							typeof (DialogResult));
 
 				dialog_result = value;
+				dialog_result_changed = true;
 				if (dialog_result != DialogResult.None && is_modal)
 					RaiseCloseEvents (false, false); // .Net doesn't send WM_CLOSE here.
 			}