Enable nullability in DomainUpDown (#6741)

* Enable nullability in DomainUpDown

* Rename owner to _owner

* Fix warning in DomainItemListAccessibleObject

src/System.Windows.Forms/src/PublicAPI.Shipped.txt

@@ -399,15 +399,15 @@ override System.Windows.Forms.CursorConverter.GetStandardValuesSupported(System.
 ~override System.Windows.Forms.Design.ComponentEditorPage.CreateParams.get -> System.Windows.Forms.CreateParams
 ~override System.Windows.Forms.Design.ToolStripItemDesignerAvailabilityAttribute.Equals(object obj) -> bool
 ~override System.Windows.Forms.Design.WindowsFormsComponentEditor.EditComponent(System.ComponentModel.ITypeDescriptorContext context, object component) -> bool
-~override System.Windows.Forms.DomainUpDown.CreateAccessibilityInstance() -> System.Windows.Forms.AccessibleObject
-~override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Add(object item) -> int
-~override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Insert(int index, object item) -> void
-~override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Remove(object item) -> void
-~override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.this[int index].get -> object
-~override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.this[int index].set -> void
-~override System.Windows.Forms.DomainUpDown.OnChanged(object source, System.EventArgs e) -> void
-~override System.Windows.Forms.DomainUpDown.OnTextBoxKeyPress(object source, System.Windows.Forms.KeyPressEventArgs e) -> void
-~override System.Windows.Forms.DomainUpDown.ToString() -> string
+override System.Windows.Forms.DomainUpDown.CreateAccessibilityInstance() -> System.Windows.Forms.AccessibleObject!
+override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Add(object? item) -> int
+override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Insert(int index, object? item) -> void
+override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.Remove(object? item) -> void
+override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.this[int index].get -> object?
+override System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection.this[int index].set -> void
+override System.Windows.Forms.DomainUpDown.OnChanged(object? source, System.EventArgs! e) -> void
+override System.Windows.Forms.DomainUpDown.OnTextBoxKeyPress(object? source, System.Windows.Forms.KeyPressEventArgs! e) -> void
+override System.Windows.Forms.DomainUpDown.ToString() -> string!
 ~override System.Windows.Forms.ErrorProvider.Site.set -> void
 override System.Windows.Forms.FileDialog.ToString() -> string!
 ~override System.Windows.Forms.FlowLayoutPanel.LayoutEngine.get -> System.Windows.Forms.Layout.LayoutEngine
@@ -1723,10 +1723,10 @@ System.Windows.Forms.DataObject.DataObject(string! format, object! data) -> void
 ~System.Windows.Forms.Design.IUIService.ShowMessage(string message, string caption, System.Windows.Forms.MessageBoxButtons buttons) -> System.Windows.Forms.DialogResult
 ~System.Windows.Forms.Design.IUIService.Styles.get -> System.Collections.IDictionary
 ~System.Windows.Forms.Design.WindowsFormsComponentEditor.EditComponent(object component, System.Windows.Forms.IWin32Window owner) -> bool
-~System.Windows.Forms.DomainUpDown.Items.get -> System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection
-~System.Windows.Forms.DomainUpDown.OnSelectedItemChanged(object source, System.EventArgs e) -> void
-~System.Windows.Forms.DomainUpDown.SelectedItem.get -> object
-~System.Windows.Forms.DomainUpDown.SelectedItem.set -> void
+System.Windows.Forms.DomainUpDown.Items.get -> System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection!
+System.Windows.Forms.DomainUpDown.OnSelectedItemChanged(object? source, System.EventArgs! e) -> void
+System.Windows.Forms.DomainUpDown.SelectedItem.get -> object?
+System.Windows.Forms.DomainUpDown.SelectedItem.set -> void
 ~System.Windows.Forms.ErrorProvider.BindToDataAndErrors(object newDataSource, string newDataMember) -> void
 ~System.Windows.Forms.ErrorProvider.CanExtend(object extendee) -> bool
 ~System.Windows.Forms.ErrorProvider.ContainerControl.get -> System.Windows.Forms.ContainerControl
@@ -7766,10 +7766,10 @@ System.Windows.Forms.DomainUpDown.DomainUpDownAccessibleObject.DomainUpDownAcces
 System.Windows.Forms.DomainUpDown.DomainUpDownItemCollection
 System.Windows.Forms.DomainUpDown.Padding.get -> System.Windows.Forms.Padding
 System.Windows.Forms.DomainUpDown.Padding.set -> void
-System.Windows.Forms.DomainUpDown.PaddingChanged -> System.EventHandler
+System.Windows.Forms.DomainUpDown.PaddingChanged -> System.EventHandler?
 System.Windows.Forms.DomainUpDown.SelectedIndex.get -> int
 System.Windows.Forms.DomainUpDown.SelectedIndex.set -> void
-System.Windows.Forms.DomainUpDown.SelectedItemChanged -> System.EventHandler
+System.Windows.Forms.DomainUpDown.SelectedItemChanged -> System.EventHandler?
 System.Windows.Forms.DomainUpDown.Sorted.get -> bool
 System.Windows.Forms.DomainUpDown.Sorted.set -> void
 System.Windows.Forms.DomainUpDown.Wrap.get -> bool

src/System.Windows.Forms/src/System/Windows/Forms/DomainUpDown.DomainItemListAccessibleObject.cs

@@ -61,7 +61,7 @@ namespace System.Windows.Forms
             {
                 if (index >= 0 && index < GetChildCount())
                 {
-                    return new DomainItemAccessibleObject(((DomainUpDown)_parent.Owner).Items[index].ToString(), this);
+                    return new DomainItemAccessibleObject(((DomainUpDown)_parent.Owner).Items[index]!.ToString(), this);
                 }
 
                 return null;

src/System.Windows.Forms/src/System/Windows/Forms/DomainUpDown.DomainUpDownItemCollection.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections;
 using System.ComponentModel;
 
@@ -17,17 +15,17 @@ namespace System.Windows.Forms
         /// </summary>
         public class DomainUpDownItemCollection : ArrayList
         {
-            readonly DomainUpDown owner;
+            private readonly DomainUpDown _owner;
 
             internal DomainUpDownItemCollection(DomainUpDown owner)
-            : base()
+                : base()
             {
-                this.owner = owner;
+                _owner = owner;
             }
 
             [Browsable(false)]
             [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
-            public override object this[int index]
+            public override object? this[int index]
             {
                 get
                 {
@@ -38,28 +36,28 @@ namespace System.Windows.Forms
                 {
                     base[index] = value;
 
-                    if (owner.SelectedIndex == index)
+                    if (_owner.SelectedIndex == index)
                     {
-                        owner.SelectIndex(index);
+                        _owner.SelectIndex(index);
                     }
 
-                    if (owner.Sorted)
+                    if (_owner.Sorted)
                     {
-                        owner.SortDomainItems();
+                        _owner.SortDomainItems();
                     }
                 }
             }
 
             /// <summary>
             /// </summary>
-            public override int Add(object item)
+            public override int Add(object? item)
             {
                 // Overridden to perform sorting after adding an item
 
                 int ret = base.Add(item);
-                if (owner.Sorted)
+                if (_owner.Sorted)
                 {
-                    owner.SortDomainItems();
+                    _owner.SortDomainItems();
                 }
 
                 return ret;
@@ -67,7 +65,7 @@ namespace System.Windows.Forms
 
             /// <summary>
             /// </summary>
-            public override void Remove(object item)
+            public override void Remove(object? item)
             {
                 int index = IndexOf(item);
 
@@ -88,27 +86,26 @@ namespace System.Windows.Forms
                 // Overridden to update the domain index if necessary
                 base.RemoveAt(item);
 
-                if (item < owner._domainIndex)
+                if (item < _owner._domainIndex)
                 {
                     // The item removed was before the currently selected item
-                    owner.SelectIndex(owner._domainIndex - 1);
+                    _owner.SelectIndex(_owner._domainIndex - 1);
                 }
-                else if (item == owner._domainIndex)
+                else if (item == _owner._domainIndex)
                 {
                     // The currently selected item was removed
-                    //
-                    owner.SelectIndex(-1);
+                    _owner.SelectIndex(-1);
                 }
             }
 
             /// <summary>
             /// </summary>
-            public override void Insert(int index, object item)
+            public override void Insert(int index, object? item)
             {
                 base.Insert(index, item);
-                if (owner.Sorted)
+                if (_owner.Sorted)
                 {
-                    owner.SortDomainItems();
+                    _owner.SortDomainItems();
                 }
             }
         }

src/System.Windows.Forms/src/System/Windows/Forms/DomainUpDown.DomainUpDownItemCompare.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections;
 using System.Globalization;
 
@@ -13,7 +11,7 @@ namespace System.Windows.Forms
     {
         private sealed class DomainUpDownItemCompare : IComparer
         {
-            public int Compare(object p, object q)
+            public int Compare(object? p, object? q)
             {
                 if (p == q)
                 {

src/System.Windows.Forms/src/System/Windows/Forms/DomainUpDown.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections;
 using System.ComponentModel;
 using System.Diagnostics;
@@ -28,13 +26,13 @@ namespace System.Windows.Forms
         /// <summary>
         ///  Allowable strings for the domain updown.
         /// </summary>
-        private DomainUpDownItemCollection _domainItems;
+        private DomainUpDownItemCollection? _domainItems;
 
         private string _stringValue = s_defaultValue;      // Current string value
         private int _domainIndex = -1;                    // Index in the domain list
         private bool _sorted;                 // Sort the domain values
 
-        private EventHandler _onSelectedItemChanged;
+        private EventHandler? _onSelectedItemChanged;
 
         private bool _inSort;
 
@@ -83,7 +81,7 @@ namespace System.Windows.Forms
 
         [Browsable(false)]
         [EditorBrowsable(EditorBrowsableState.Never)]
-        public new event EventHandler PaddingChanged
+        public new event EventHandler? PaddingChanged
         {
             add => base.PaddingChanged += value;
             remove => base.PaddingChanged -= value;
@@ -132,7 +130,7 @@ namespace System.Windows.Forms
         [Browsable(false)]
         [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
         [SRDescription(nameof(SR.DomainUpDownSelectedItemDescr))]
-        public object SelectedItem
+        public object? SelectedItem
         {
             get
             {
@@ -142,7 +140,6 @@ namespace System.Windows.Forms
             set
             {
                 // Treat null as selecting no item
-                //
                 if (value is null)
                 {
                     SelectedIndex = -1;
@@ -150,7 +147,6 @@ namespace System.Windows.Forms
                 else
                 {
                     // Attempt to find the given item in the list of items
-                    //
                     for (int i = 0; i < Items.Count; i++)
                     {
                         if (value.Equals(Items[i]))
@@ -208,7 +204,7 @@ namespace System.Windows.Forms
         /// </summary>
         [SRCategory(nameof(SR.CatBehavior))]
         [SRDescription(nameof(SR.DomainUpDownOnSelectedItemChangedDescr))]
-        public event EventHandler SelectedItemChanged
+        public event EventHandler? SelectedItemChanged
         {
             add => _onSelectedItemChanged += value;
             remove => _onSelectedItemChanged -= value;
@@ -229,7 +225,6 @@ namespace System.Windows.Forms
         public override void DownButton()
         {
             // Make sure domain values exist, and there are >0 items
-            //
             if (_domainItems is null)
             {
                 return;
@@ -326,11 +321,11 @@ namespace System.Windows.Forms
             {
                 if (complete)
                 {
-                    found = Items[index].ToString().Equals(text);
+                    found = Items[index]!.ToString()!.Equals(text);
                 }
                 else
                 {
-                    found = Items[index].ToString().ToUpper(CultureInfo.InvariantCulture).StartsWith(text);
+                    found = Items[index]!.ToString()!.ToUpper(CultureInfo.InvariantCulture).StartsWith(text);
                 }
 
                 if (found)
@@ -355,7 +350,7 @@ namespace System.Windows.Forms
         ///  values is called OnSelectedItemChanged - so just forward it to that
         ///  function.
         /// </summary>
-        protected override void OnChanged(object source, EventArgs e)
+        protected override void OnChanged(object? source, EventArgs e)
         {
             OnSelectedItemChanged(source, e);
         }
@@ -365,7 +360,7 @@ namespace System.Windows.Forms
         ///  event, using the input character to find the next matching item in our
         ///  item collection.
         /// </summary>
-        protected override void OnTextBoxKeyPress(object source, KeyPressEventArgs e)
+        protected override void OnTextBoxKeyPress(object? source, KeyPressEventArgs e)
         {
             if (ReadOnly)
             {
@@ -398,7 +393,7 @@ namespace System.Windows.Forms
         /// <summary>
         ///  Raises the <see cref="SelectedItemChanged"/> event.
         /// </summary>
-        protected void OnSelectedItemChanged(object source, EventArgs e)
+        protected void OnSelectedItemChanged(object? source, EventArgs e)
         {
             // Call the event handler
             _onSelectedItemChanged?.Invoke(this, e);
@@ -421,11 +416,10 @@ namespace System.Windows.Forms
             }
 
             // If the selected index has changed, update the text
-            //
             _domainIndex = index;
             if (_domainIndex >= 0)
             {
-                _stringValue = _domainItems[_domainIndex].ToString();
+                _stringValue = _domainItems[_domainIndex]!.ToString()!;
                 UserEdit = false;
                 UpdateEditText();
             }