Hello,

RadPropertyGrid does not properly intersect properties when what is set as SelectedObjects implements the ICustomTypeDescriptor interface. However, the .Net Framework PropertyGrid does not have this problem.

To reproduce the problem, use the attached project.

When setting SelectedObject a ReadOnlyAttribute applies to the grid. But when wrapping it in an object[] and assign it to SelectedObjects the grid allows editing.

Sample application included.

Currently, the only possible way to set the value to null is to select the whole text and press the Delete key.

If the value is cleared by the backspace key, it is restored when the control loses focus.

If the value is cleared by multiple times clicking the delete key and the cursor is in the first position, the previous value is restored when the control loses focus.

Workaround:
Subscribe to the TextChanged event of the spin editor and explicitly set the NullableValue of the BaseSpinEditorElement:

this.radPropertyGrid1.EditorInitialized += this.RadPropertyGrid1_EditorInitialized;

private void RadPropertyGrid1_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
{
    if (e.Editor is PropertyGridSpinEditor spinEdit)
    {
        if (spinEdit.EditorElement is BaseSpinEditorElement editorElement && editorElement.EnableNullValueInput)
        {
            editorElement.TextChanged -= this.EditorElement_TextChanged;
            editorElement.TextChanged += this.EditorElement_TextChanged;
        }
    }
}

private void EditorElement_TextChanged(object sender, EventArgs e)
{
    if (sender is BaseSpinEditorElement editorElement && string.IsNullOrWhiteSpace(editorElement.Text))
    {
        editorElement.NullableValue = null;
    }
}

Workaround:
 Private Sub RadPropertyGrid1_EditorRequired(sender As Object, e As PropertyGridEditorRequiredEventArgs) Handles RadPropertyGrid1.EditorRequired
     Dim te As PropertyGridTableElement = TryCast(sender, PropertyGridTableElement)
     If e.EditorType = GetType(PropertyGridSpinEditor) Then
         Dim editor As New CustomPropertyGridSpinEditor
         If editor IsNot Nothing AndAlso te IsNot Nothing Then
             Dim type As Type = RadPropertyGrid1.SelectedObject.[GetType]().GetProperty(e.Item.Name).PropertyType
             If type = GetType(System.Double) Then
                 DirectCast(editor.EditorElement, BaseSpinEditorElement).DecimalPlaces = 4
                 e.Editor = editor
             End If
         End If
     End If
 End Sub

 Public Class CustomPropertyGridSpinEditor
     Inherits PropertyGridSpinEditor
     Public Overrides Sub Initialize(owner As Object, value As Object)
         Dim decimalPlaces As Integer = Me.DecimalPlaces
         MyBase.Initialize(owner, value)

         Dim element As PropertyGridItemElement = TryCast(owner, PropertyGridItemElement)
         Dim item As PropertyGridItem = TryCast(element.Data, PropertyGridItem)
         Dim editedType As Type = item.PropertyType

        If ((editedType = GetType(Decimal) OrElse editedType = GetType(Double) OrElse editedType = GetType(Single)) AndAlso decimalPlaces <> 0) Then
         DirectCast(Me.EditorElement, BaseSpinEditorElement).DecimalPlaces = decimalPlaces
         Me.Value = value
       End If
     End Sub
 End Class

To reproduce: run the attached sample project and follow the steps from the gif file.

Workaround: cancel the edit operation when handling the MouseDown event of RadPropertyGrid:

        private void radPropertyGrid1_MouseDown(object sender, MouseEventArgs e)
        {
            var elementUnderMouse = this.radPropertyGrid1.ElementTree.GetElementAtPoint(e.Location).FindAncestor<RadScrollBarElement>();
            if (elementUnderMouse!=null)
            {
                this.radPropertyGrid1.CancelEdit();
            } 
        }

Use the editor from the following article to reproduce: https://docs.telerik.com/devtools/winforms/propertygrid/editors/using-custom-editor

Workaround:
void TrackBarEditor_ValueChanged(object sender, EventArgs e)
{
    PropertyGridItemElement owner = this.OwnerElement as PropertyGridItemElement;

    if (owner != null)
    {
        var method = owner.PropertyTableElement.GetType().GetMethod("OnValueChanged", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        method.Invoke(owner.PropertyTableElement, new object[] { this, EventArgs.Empty });

    }
}

To reproduce:

Public Class RadForm1
    Sub New()        
        InitializeComponent()
        RadPropertyGrid1.SelectedObject = New MyProperties
    End Sub

    Public Class MyProperties

        Private _height As Integer = 70
        <Browsable(True)> <Category("Rows")> <DisplayName("Height")> _
        <Description("Sets the height of the row. Range 70 to 200.")> _
        <RadRange(70, 200)> _
        Public Property Height() As Integer
            Get
                Return _height
            End Get
            Set(ByVal Value As Integer)
                _height = Value
            End Set
        End Property
    End Class
End Class

When you activate the editor you will notice that you are allowed to enter values outside the specified range 7-200.

Workaround:

AddHandler Me.RadPropertyGrid1.EditorInitialized, AddressOf PropertyGridEditorInitialized

    Private Sub PropertyGridEditorInitialized(sender As Object, e As PropertyGridItemEditorInitializedEventArgs)
        Dim spinEditor As PropertyGridSpinEditor = TryCast(e.Editor, PropertyGridSpinEditor)
        If spinEditor IsNot Nothing Then
            spinEditor.MinValue = 70
            spinEditor.MaxValue = 200
        End If

    End Sub

Use attached to reproduce. 

Workaround
radPropertyGrid1.ItemSpacing = 1;

To reproduce:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);

Please refer to the attached gif file.

Workaround:

            this.radPropertyGrid1.SelectedObject = this;             
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.MinSize = new Size(0, 60);
            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.MinSize = new Size(0,20);

            this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpTitleElement.PropertyChanged += HelpTitleElement_PropertyChanged;

        private void HelpTitleElement_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "Bounds")
            {
                if (this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location.Y != 20)
                {
                    this.radPropertyGrid1.PropertyGridElement.SplitElement.HelpElement.HelpContentElement.Location = new Point(0, 20);
                }
            }
        }

Note: the description element may be floating but it doesn't overlap the title. 

How to reproduce: associate the control with an object having a Font property. It can be the form itself, then try and change the font-size, e.g: -1.

The standard property grid displays a message box with the error.

Workaround handle the RadPropertyGrid.EditorInitialized event:
private void RadPropertyGrid_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
{
    PropertyGridSpinEditor editor = e.Editor as PropertyGridSpinEditor;
    if (editor != null && e.Item.Parent != null && e.Item.Parent.Name == "Font" && e.Item.Name == "Size")
    {
        editor.MinValue = 1;
    }
}

To reproduce: use the following code snippet and follow the steps from the gif file:

            PropertyStoreItem item1 = new PropertyStoreItem(typeof(string), "Test1", "Test1");
            PropertyStoreItem item2 = new PropertyStoreItem(typeof(string), "Test2", "Test2");
          
            RadPropertyStore store = new RadPropertyStore();
            store.Add(item1);
            store.Add(item2); 
            this.radPropertyGrid1.SelectedObject = store;

            this.radPropertyGrid1.ToolbarVisible = true;

Workaround: close the editor programmatically when the search box gets focus.

this.radPropertyGrid1.PropertyGridElement.ToolbarElement.SearchTextBoxElement.TextBoxItem.GotFocus += TextBoxItem_GotFocus;

        private void TextBoxItem_GotFocus(object sender, EventArgs e)
        {
            this.radPropertyGrid1.EndEdit();
        }

Please refer to the attached video illustrating the incorrect behavior of the context menu.

Workaround:

        public RadForm1()
        {
            InitializeComponent();

            this.radPropertyGrid1.SelectedObject = this;
            this.radPropertyGrid1.ToolbarVisible = true;

            this.radPropertyGrid1.RadContextMenu = new CustomPropertyGridDefaultContextMenu(this.radPropertyGrid1.PropertyGridElement.PropertyTableElement);
        }

        public class CustomPropertyGridDefaultContextMenu : Telerik.WinControls.UI.PropertyGridDefaultContextMenu
        {
            PropertyGridTableElement tableElement;

            public CustomPropertyGridDefaultContextMenu(PropertyGridTableElement propertyGridElement) : base(propertyGridElement)
            {
                tableElement = propertyGridElement;
            }

            protected override void OnDropDownOpening(CancelEventArgs args)
            {
                base.OnDropDownOpening(args);
                PropertyGridItemBase item = this.tableElement.SelectedGridItem;
                if (item != null)
                {
                    if (!(item is PropertyGridGroupItem))
                    {
                        this.EditMenuItem.Visibility = ElementVisibility.Visible;
                        this.ResetMenuItem.Visibility = ElementVisibility.Visible;
                    }
                }
            }
        }

How to reproduce: check the attached screenshot

Workaround: use the attached custom theme

To reproduce:
- Add RadPropertyGrid to a form and set the theme to MaterialTeal. The issue is observed in the ThemeViewer as well.

Workaround:
radPropertyGrid1.PropertyGridElement.ToolbarElement.AlphabeticalToggleButton.TextWrap = true;
radPropertyGrid1.PropertyGridElement.ToolbarElement.CategorizedToggleButton.TextWrap = true;
//or

 radPropertyGrid1.PropertyGridElement.ToolbarElementHeight = 68;

To reproduce: please refer to the attached sample project. Try to select a new value from the drop-down editor and press Yes from the message box.

Workaround: use the RadPropertyGrid.PropertyValueChanging event to confirm the property changing: 

private void radPropertyGrid1_PropertyValueChanging(object sender, Telerik.WinControls.UI.PropertyGridItemValueChangingEventArgs e)
{
    e.Cancel = (MessageBox.Show("Are you sure you want to change this?", "Question", MessageBoxButtons.YesNo) != DialogResult.Yes);
}

Workaround use the attached custom theme: http://docs.telerik.com/devtools/winforms/themes/using-custom-themes

To reproduce: subscribe to the RadPropertyGrid.PropertyValidating event and apply ErrorMessage in some cases. If the validation fails, the error indicator is not visible in Windows8, VisualStudio2012Dark, Aqua. However, the error message is displayed as expected.

Workaround: assign an image for the ErrorIndicator

private void radPropertyGrid1_ItemFormatting(object sender, PropertyGridItemFormattingEventArgs e)
{
    PropertyGridItemElement itemElement = e.VisualElement as PropertyGridItemElement;
    if (itemElement != null)
    {
        ((PropertyGridTextElement)itemElement.TextElement).ErrorIndicator.Image = Properties.Resources.error;
    }
}