When you define a property of List<string> type for a control, if you try to edit the property in PropertyGrid, a collection editor form will open and if you click on add button on the editor form, you will face with an error:

Constructor on type ‘System.String’ not found.

How can we edit the list in a collection editor form without facing such error message? Is there any UITypeEditor suitable to edit List<string> without problem? In this post, I’ll show how you can edit a List<string> in property grid without any problem.

Let’s say we have a control containing the following property:

private List<string> myList = new List<string>();
public List<string> MyList {
    get {
        return myList;
    }
    set {
        myList = value;
    }
}

If it was string[] we were safe and without doing anything special, the property grid would show a standard dialog containing a multi-line text box to edit string array and each line will be an element in the array. But the case for List<string> is different.

To edit List<string> in property grid, you can use either of the following options:

• StringCollectionEditor which shows a dialog containing a multi-line text box to edit elements
• Create a custom CollectionEditor to edit items in a collection editor dialog

Option 1 – StringCollectionEditor

private List<string> myList = new List<string>();
[Editor("System.Windows.Forms.Design.StringCollectionEditor, " +
    "System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a",
    typeof(UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public List<string> MyList {
    get {
        return myList;
    }
    set {
        myList = value;
    }
}

Option 2 – Custom CollectionEditor

First create the custom editor:

//You need to add reference to System.Design
public class MyStringCollectionEditor : CollectionEditor {
    public MyStringCollectionEditor() : base(type: typeof(List<String>)) { }
    protected override object CreateInstance(Type itemType) {
        return string.Empty;
    }
}

Then decorate the property with the editor attribute:

private List<string> myList = new List<string>();
[Editor(typeof(MyStringCollectionEditor), typeof(UITypeEditor))]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Content)]
public List<string> MyList {
    get {
        return myList;
    }
    set {
        myList = value;
    }
}