Cascading ComboBoxes in PropertyGrid

Environment

Product Version	Product	Author
2022.2.622	RadPropertyGrid for WinForms	Desislava Yordanova

Description

RadPropertyGrid uses a PropertyGridDropDownListEditor for editing properties that have a type converter supporting standard values and do not have a UITypeEditor. When the editor is activated, a list of options is presented to the end user to choose from.

This article demonstrates a sample approach how to use the PropertyGridDropDownListEditor to achieve the well-known scenario for cascading comboboxes. Consider that you have Category and Product properties. When you select a certain category, then the listed products should be relevant for the selected category.

Solution

For this example we will use the Northwind database and its Categories and Products tables. When an editor is required in RadPropertyGrid, a PropertyGridDropDownListEditor will be created filled with the respective DataSource collection. For the Product property, the assigned Northwind.Products table will be filtered according to the selected category in the Category property.

public RadForm1()
{
    InitializeComponent();

    PropertyStoreItem categoryItem = new PropertyStoreItem(typeof(string), "Category","Beverages");
    PropertyStoreItem productItem = new PropertyStoreItem(typeof(string), "Product","Chai");
    RadPropertyStore store = new RadPropertyStore();
    store.Add(categoryItem);
    store.Add(productItem); 
    this.radPropertyGrid1.SelectedObject = store;
    this.radPropertyGrid1.EditorRequired += radPropertyGrid1_EditorRequired;
    this.radPropertyGrid1.EditorInitialized += radPropertyGrid1_EditorInitialized;
    this.radPropertyGrid1.Edited += RadPropertyGrid1_Edited;
}

private void RadPropertyGrid1_Edited(object sender, PropertyGridItemEditedEventArgs e)
{
    if (e.Item.Label == "Category")
    {
        lastSelectedCategory = ((PropertyGridItem)e.Item).Value + "";
    }
}

string lastSelectedCategory = "Beverages";
private void radPropertyGrid1_EditorInitialized(object sender, PropertyGridItemEditorInitializedEventArgs e)
{
    PropertyGridDropDownListEditor editor = e.Editor as PropertyGridDropDownListEditor;
    if (editor != null)
    {
       BaseDropDownListEditorElement el = editor.EditorElement as BaseDropDownListEditorElement;
       el.SelectedValue = ((PropertyGridItem)e.Item).Value;
        if (e.Item.Label=="Category")
        {
            el.SelectedIndexChanged -= El_SelectedIndexChanged;
            el.SelectedIndexChanged += El_SelectedIndexChanged;
        }
    }
}

private void El_SelectedIndexChanged(object sender, Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
{
    RadPropertyStore store = this.radPropertyGrid1.SelectedObject as RadPropertyStore;
    store["Product"].Value = null;
}

private void radPropertyGrid1_EditorRequired(object sender, PropertyGridEditorRequiredEventArgs e)
{
    if (e.Item.Label == "Category")
    {
        PropertyGridDropDownListEditor editor = new PropertyGridDropDownListEditor();
        BaseDropDownListEditorElement el = editor.EditorElement as BaseDropDownListEditorElement; 
        el.DisplayMember = "CategoryName";
        el.ValueMember = "CategoryName";
        el.DataSource = this.categoriesBindingSource;
        e.Editor = editor;
    }
    else if (e.Item.Label == "Product")
    {
        PropertyGridDropDownListEditor editor = new PropertyGridDropDownListEditor();
        BaseDropDownListEditorElement el = editor.EditorElement as BaseDropDownListEditorElement;
        el.DisplayMember = "ProductName";
        el.ValueMember = "ProductName";
        DataTable productsTable = ((DataSet)this.productsBindingSource.DataSource).Tables["Products"];
        DataView dv = new DataView(productsTable);

        dv.RowFilter = "CategoryID="+ GetCategoryIDByName(lastSelectedCategory);  
        el.DataSource = dv;
        e.Editor = editor;
    }
}

private int GetCategoryIDByName(string lastSelectedCategory)
{
    int id = -1;
    DataTable categoriesTable = ((DataSet)this.productsBindingSource.DataSource).Tables["Categories"];
    foreach (NwindDataSet.CategoriesRow row in categoriesTable.Rows)
    {
        if (row.CategoryName == lastSelectedCategory)
        {
            id = row.CategoryID;
            break;
        }
    }
    return id;
}

private void RadForm1_Load(object sender, EventArgs e)
{
    this.productsTableAdapter.Fill(this.nwindDataSet.Products);
    this.categoriesTableAdapter.Fill(this.nwindDataSet.Categories);
}

Public Sub New()
    InitializeComponent()
    Dim categoryItem As PropertyStoreItem = New PropertyStoreItem(GetType(String), "Category", "Beverages")
    Dim productItem As PropertyStoreItem = New PropertyStoreItem(GetType(String), "Product", "Chai")
    Dim store As RadPropertyStore = New RadPropertyStore()
    store.Add(categoryItem)
    store.Add(productItem)
    Me.RadPropertyGrid1.SelectedObject = store
    AddHandler Me.RadPropertyGrid1.EditorRequired, AddressOf radPropertyGrid1_EditorRequired
    AddHandler Me.RadPropertyGrid1.EditorInitialized, AddressOf radPropertyGrid1_EditorInitialized
    AddHandler Me.RadPropertyGrid1.Edited, AddressOf RadPropertyGrid1_Edited
End Sub

Private Sub RadPropertyGrid1_Edited(ByVal sender As Object, ByVal e As PropertyGridItemEditedEventArgs)
    If e.Item.Label = "Category" Then
        lastSelectedCategory = (CType(e.Item, PropertyGridItem)).Value & ""
    End If
End Sub

Private lastSelectedCategory As String = "Beverages"

Private Sub radPropertyGrid1_EditorInitialized(ByVal sender As Object, ByVal e As PropertyGridItemEditorInitializedEventArgs)
    Dim editor As PropertyGridDropDownListEditor = TryCast(e.Editor, PropertyGridDropDownListEditor)

    If editor IsNot Nothing Then
        Dim el As BaseDropDownListEditorElement = TryCast(editor.EditorElement, BaseDropDownListEditorElement)
        el.SelectedValue = (CType(e.Item, PropertyGridItem)).Value

        If e.Item.Label = "Category" Then
            RemoveHandler el.SelectedIndexChanged, AddressOf El_SelectedIndexChanged
            AddHandler el.SelectedIndexChanged, AddressOf El_SelectedIndexChanged
        End If
    End If
End Sub

Private Sub El_SelectedIndexChanged(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.Data.PositionChangedEventArgs)
    Dim store As RadPropertyStore = TryCast(Me.RadPropertyGrid1.SelectedObject, RadPropertyStore)
    store("Product").Value = Nothing
End Sub

Private Sub radPropertyGrid1_EditorRequired(ByVal sender As Object, ByVal e As PropertyGridEditorRequiredEventArgs)
    If e.Item.Label = "Category" Then
        Dim editor As PropertyGridDropDownListEditor = New PropertyGridDropDownListEditor()
        Dim el As BaseDropDownListEditorElement = TryCast(editor.EditorElement, BaseDropDownListEditorElement)
        el.DisplayMember = "CategoryName"
        el.ValueMember = "CategoryName"
        el.DataSource = Me.CategoriesBindingSource
        e.Editor = editor
    ElseIf e.Item.Label = "Product" Then
        Dim editor As PropertyGridDropDownListEditor = New PropertyGridDropDownListEditor()
        Dim el As BaseDropDownListEditorElement = TryCast(editor.EditorElement, BaseDropDownListEditorElement)
        el.DisplayMember = "ProductName"
        el.ValueMember = "ProductName"
        Dim productsTable As DataTable = (CType(Me.ProductsBindingSource.DataSource, DataSet)).Tables("Products")
        Dim dv As DataView = New DataView(productsTable)
        dv.RowFilter = "CategoryID=" & GetCategoryIDByName(lastSelectedCategory)
        el.DataSource = dv
        e.Editor = editor
    End If
End Sub

Private Function GetCategoryIDByName(ByVal lastSelectedCategory As String) As Integer
    Dim id As Integer = -1
    Dim categoriesTable As DataTable = (CType(Me.ProductsBindingSource.DataSource, DataSet)).Tables("Categories")

    For Each row As NwindDataSet.CategoriesRow In categoriesTable.Rows

        If row.CategoryName = lastSelectedCategory Then
            id = row.CategoryID
            Exit For
        End If
    Next

    Return id
End Function
Private Sub RadForm1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    Me.ProductsTableAdapter.Fill(Me.NwindDataSet.Products)
    Me.CategoriesTableAdapter.Fill(Me.NwindDataSet.Categories)

End Sub

See Also

• Editors