Question

I have attempted to create my own UITypeEditor but the EditValue method never gets called

public class BoundedTextEditor : UITypeEditor
{

    public override System.Drawing.Design.UITypeEditorEditStyle GetEditStyle(System.ComponentModel.ITypeDescriptorContext context)
    {
        return UITypeEditorEditStyle.None;
    }

    public override object EditValue(System.ComponentModel.ITypeDescriptorContext context, System.IServiceProvider provider, object value)
    {
        if (value.GetType() != typeof(string)) return value;
        var editorService = (IWindowsFormsEditorService)provider.GetService(typeof(IWindowsFormsEditorService));
        if (editorService != null)
        {
            var textBox = new TextBox { Text = value.ToString(), Size = new Size(200, 100), MaxLength = 3 };
            editorService.DropDownControl(textBox);
            return textBox.Text;
        }
        return value;
    }

}

Used like this:

[Editor(typeof(BoundedTextEditor), typeof(UITypeEditor))]
public string KeyTip
{
    get
    {
        return _keyTip;
    }
    set
    {
        _keyTip = value;
    }
}

Here I have attempted to limit the string to 3 characters, would be better if that can be defined via an attribute.

Answer 1

Since you want to show a TextBox in a drop-down area beneath the property, change your implementation of GetEditStyle to return UITypeEditorEditStyle.DropDown instead of UITypeEditorEditStyle.None.

This will show a drop-down arrow next to the property like you see on a ComboBox, clicking on the arrow will then call your EditValue method to show a drop-down text box to edit the property value.