Please run the sample project on a monitor with 150 DPI scaling. You will notice that the first time the drop down is not scaled properly and it is clipped. However, each next opening of the drop down, the popup is scaled correctly:

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

The clients needs to use a PropertyGridDropDownListEditor and confirms the new value whenever a new selection is made. The attached gif file illustrates how to replicate the error using the following code snippet:

        public RadForm1()
        {
            InitializeComponent();

            this.radPropertyGrid1.SelectedObject = this; 
            this.radPropertyGrid1.EditorInitialized += radPropertyGrid1_EditorInitialized; 
        } 

        private void radPropertyGrid1_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
        {
            PropertyGridDropDownListEditor ddl = e.Editor as PropertyGridDropDownListEditor;
            if (ddl != null)
            {
                ddl.LoopValuesOnDoubleClick = false;
                BaseDropDownListEditorElement element = ddl.EditorElement as BaseDropDownListEditorElement;

                if (element != null)
                { 
                    element.SelectedValueChanged -= Element_SelectedValueChanged;
                    element.SelectedValueChanged += Element_SelectedValueChanged;
                }
            }
        }
 
        private void Element_SelectedValueChanged(object sender, Telerik.WinControls.UI.Data.ValueChangedEventArgs e)
        {
            this.radPropertyGrid1.EndEdit();
        }

Workaround:

        public RadForm1()
        {
            InitializeComponent();

            this.radPropertyGrid1.SelectedObject = this;  

            this.radPropertyGrid1.ValueChanged += RadPropertyGrid1_ValueChanged;
        }

        private void RadPropertyGrid1_ValueChanged(object sender, EventArgs e)
        {
            if (this.radPropertyGrid1.ActiveEditor is PropertyGridDropDownListEditor)
            {
                this.radPropertyGrid1.EndEdit();
            }
        }

Problem: I'd like to filter the properties to be displayed by their category names defined by the Category attribute. Based on the doc here (https://docs.telerik.com/devtools/winforms/controls/propertygrid/features/filtering), my understanding is to add a FilterDescriptor like this: New FilterDescriptor ("Category", FilterOperator.Contains, "some category name"). But it turned out to only filter by property name, not category name. Any misunderstanding or possible issue? Thank you for looking into this.

Reproduce:

1. Define a class like this:

    Private Class TestClass
        <Category("Cat1")> Public Property Property1 As Integer = 1
        <Category("Cat1")> Public Property Property2 As String = "Test 2"
        <Category("Cat2")> Public Property Property3 As String = "Test 3"
    End Class

2. Initialize a RadPropertyGrid in the Form.Load event:

        Dim testObj As New TestClass
        RadPropertyGrid1.EnableFiltering = True
        Dim filter As New FilterDescriptor("Category", FilterOperator.Contains, "2")
        RadPropertyGrid1.FilterDescriptors.Add(filter)
        RadPropertyGrid1.SelectedObject = testObj

3. The right property to be displayed should be Property3, but it turned out to be Property2

Example project: attached.

Thank you team!

Use the following code snippet and try to edit the Height. You will notice that the sub-items' order is changed:

            RadPropertyStore store = new RadPropertyStore();
            PropertyStoreItem sizeItem = new PropertyStoreItem(typeof(System.Drawing.Size), "Size", new System.Drawing.Size(100, 25), "The size of the control in pixels.", "Layout");
            store.Add(sizeItem);

            this.radPropertyGrid1.SelectedObject = store;
            this.radPropertyGrid1.SortOrder = SortOrder.Ascending;
            this.radPropertyGrid1.PropertySort = PropertySort.Alphabetical;

1. Create a custom property item

2. Enable grouping

3.Scroll up and down

4.NullReferenceException occurs

Hello, 

we are trying to use RadPropertyGrid to show the properties of some objects listed in a RadGrdiView. 

We use ExpandableObject to expand our custom property, but we have some problems when we try to show the properties of multiple selected items, when the values of the attribute of the property are not the same in all the selected objects. We tried to use PropertyGrid of Winform and we don't have this problem. 

Thank you.

Currently, the ExpandableObjectConverter is the appropriate solution for adding nested properties in RadPropertyGrid. Using TypeConverters is quite a flexible mechanism that RadPropertyGrid offers: https://docs.telerik.com/devtools/winforms/controls/propertygrid/type-converters

It would be nice to have a more flexible and easy approach, e.g. PropertyStoreItem .Items collection that allows you to add nested properties.

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 });

    }
}

When you have  a property that is bool? or ToggleState, it would be good to have three-state functionality for the PropertyGridCheckBoxItemElement.

Office2010silver theme showing different result with  2017.2.613 version my font size became very small.

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;
    }
}

This should work similar to RadGridView. Once should be able to manually set the height of on individual rows as well.

The incorrect behavior is also observed if the SelectedObject is changed.

How to reproduce:

public partial class RadForm1 : RadForm
{
    public RadForm1()
    {
        this.InitializeComponent();
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        this.radPropertyGrid1.EnableSorting = true;
        this.radPropertyGrid1.SelectedObject = new TestObject();
        foreach (var item in this.radPropertyGrid1.Items)
        {
            if (item.Name == "A")
            {
                item.SortOrder = 2;
            }
            else if (item.Name == "B")
            {
                item.SortOrder = 1;
            }
            else
            {
                item.SortOrder = 0;
            }
        }

        this.radPropertyGrid1.PropertySort = PropertySort.NoSort;
    }
}

public class TestObject
{
    public int A { get; set; }
    public int C { get; set; }
    public int B { get; set; }
}

Workaround:
1. Use attributes in the model class:
public class TestObject
{
    [RadSortOrder(2)]
    public int A { get; set; }
    [RadSortOrder(0)]
    public int C { get; set; }
    [RadSortOrder(1)]
    public int B { get; set; }
}

2. Alternatively, toggle the PropertySort property in the Shown event of the form:
public partial class RadForm1 : RadForm
{
    public RadForm1()
    {
        this.InitializeComponent();
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        this.radPropertyGrid1.EnableSorting = true;
        this.radPropertyGrid1.SelectedObject = new TestObject();
        foreach (var item in this.radPropertyGrid1.Items)
        {
            if (item.Name == "A")
            {
                item.SortOrder = 2;
            }
            else if (item.Name == "B")
            {
                item.SortOrder = 1;
            }
            else
            {
                item.SortOrder = 0;
            }
        }

        this.radPropertyGrid1.PropertySort = PropertySort.NoSort;
    }

    protected override void OnShown(EventArgs e)
    {
        base.OnShown(e);

        this.radPropertyGrid1.PropertySort = PropertySort.Alphabetical;
        this.radPropertyGrid1.PropertySort = PropertySort.NoSort;
    }
}

public class TestObject
{
    public int A { get; set; }
    public int C { get; set; }
    public int B { get; set; }
}

To reproduce:

    Sub New()

        InitializeComponent()

        Dim intItem As New PropertyStoreItem(GetType(Integer), "Integer", 1)
        Dim floatItem As New PropertyStoreItem(GetType(Single), "Float", 1.0F, "Property storing a floating point value.")
        Dim stringItem As New PropertyStoreItem(GetType(String), "String", "telerik", "Property storing a string value", "Telerik")
        Dim fontItem As New PropertyStoreItem(GetType(Font), "Font", New Font("Arial", 12, FontStyle.Italic), "Property containing Font value")

        fontItem.Attributes.Add(New ReadOnlyAttribute(True))
        floatItem.Attributes.Add(New ReadOnlyAttribute(True))
        Dim store As New RadPropertyStore
        store.Add(intItem)
        store.Add(floatItem)
        store.Add(stringItem)
        store.Add(fontItem)
        Me.RadPropertyGrid1.SelectedObject = store
    End Sub

Try to edit either the "Float" or the "Font" property. The editor will be activated although it doesn't have to.

Workaround: cancel the Editing event

    Private Sub RadPropertyGrid1_Editing(sender As Object, e As PropertyGridItemEditingEventArgs)
        If e.Item.Name = "Font" Then
            e.Cancel = True
        End If 
    End Sub