How can I use a WinForms PropertyGrid to edit a list of strings?

Question

In my application I have a property grid to allow users to change settings. This works fine for strings and other value properties, but what I need now is a list of strings that can be edited by users.

The problem is that if I have MyPropertyGrid.SelectedObject = new { Test = new List<string>() }; in my code and the user attempts to edit the Test property, when they click on the Add button, the following error occurs:

 Constructor on type 'System.String' not found 

This makes sense as strings are immutable. However, I still need some way to store multiple strings (or string-like data) in a property grid.

Does anyone have any ideas on how I can accomplish this?

Answer 1

Yes, you can specify an System.ComponentModel.Editor attribute on your list of strings, with StringCollectionEditor as the editor. You need to add a reference to System.Design.Dll to your project, in order for this to compile.

Example, suppose your object is like this:

[DefaultProperty("Name")] public class CustomObject {     [Description("Name of the thing")]     public String Name { get; set; }      [Description("Whether activated or not")]     public bool Activated { get; set; }      [Description("Rank of the thing")]     public int Rank { get; set; }      [Description("whether to persist the settings...")]     public bool Ephemeral { get; set; }      [Description("extra free-form attributes on this thing.")]     [Editor(@"System.Windows.Forms.Design.StringCollectionEditor," +         "System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",        typeof(System.Drawing.Design.UITypeEditor))]     [TypeConverter(typeof(CsvConverter))]     public List<String> ExtraStuff     {         get         {             if (_attributes == null)                 _attributes = new List<String>();             return _attributes;         }     }     private List<String> _attributes; } 

The property grid for that looks like this:

Click on the ... and you get:

If you don't like the builtin collection editor, you can implement your own custom collection editor.

My example shows the use of a TypeConverter attribute. If you don't do that, then the list displays in the prop grid as "(Collection)". The TypeConverter gets it to display as something intelligent. For example, to display a short string representation of the collection in the property grid, like this:

...the TypeConverter is like this:

public class CsvConverter : TypeConverter {     // Overrides the ConvertTo method of TypeConverter.     public override object ConvertTo(ITypeDescriptorContext context,        CultureInfo culture, object value, Type destinationType)     {         List<String> v = value as List<String>;         if (destinationType == typeof(string))         {             return String.Join(",", v.ToArray());          }         return base.ConvertTo(context, culture, value, destinationType);     } } 

You don't need a setter on the List<String>, because the collection editor doesn't set that property, it merely adds or removes entries to the property. So just provide the getter.