A flag editor

Thierry Bouquain

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17 Oct 2002

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This piece of code is the implementation of a simple flags editor. It can be used to edit flags in a property grid.

Introduction

This editor displays a dropdown control holding a CheckedListBox with all the values of an enumeration.

Using the FlagsEditor

You just have to put the Editor attributes on an enumeration to link it with the FlagsEditor. A Description attribute can also be added to each value. It will be shown as a tooltip on the CheckedListBox items.

Here is a sample.

[Flags,
  Editor(typeof(STUP.ComponentModel.Design.FlagsEditor), 
  typeof(System.Drawing.Design.UITypeEditor))]
public enum EnumerationTest
{
    [Description("Description for the first tested value.")]
    firstValue = 1,
    [Description("Description for the second tested value.")]
    secondValue = 2,
    [Description("Description for the third tested value.")]
    thirdValue = 4
}

How does it work ?

The Editor is just one class that inherits UITypeEditor. The behavior of Editor is controlled by two functions.

GetEditStyle

This function is used for controlling the appearance of the small button in the property grid. In this sample a dropdown arrow will be shown.

public override UITypeEditorEditStyle 
       GetEditStyle(ITypeDescriptorContext context) 
{
    return UITypeEditorEditStyle.DropDown;
}

EditValue

This function is called when the user clicks on the small button.

public override object EditValue(ITypeDescriptorContext context, 
        IServiceProvider provider, object value) 
{
    if (context != null
        && context.Instance != null
        && provider != null) 
    {

        // Get an instance of the IWindowsFormsEditorService. 
        edSvc = (IWindowsFormsEditorService)provider.GetService
                            (typeof(IWindowsFormsEditorService));

        if (edSvc != null) 
        {
            // Create a CheckedListBox
            clb = new CheckedListBox();

            ...

            // Show our CheckedListbox as a DropDownControl. 
            // This methods returns only when
            // the dropdowncontrol is closed
            edSvc.DropDownControl(clb);


            // return the right enum value
            // corresponding to the result
            return ...
        }
    }

    return value;
}

The DropDownControl can be closed by calling the edSvc.CloseDropDown() function.

For a complete example, just download the source file.

License

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