A PropertyGrid gotcha

In a nutshell, when placed in a PropertyGrid, objects that use the same DisplayNameAttribute in different categories lead to surprising selection behavior.

I decline to call it a bug because I suspect the authors of the framework would claim this is how it's supposed to behave, but it's still the sort of thing that can trip developers up. Imagine you set a PropertyGrid's SelectedObject to an instance of this class:

class Demo
{
    [Category("Category1")]
    [DisplayName("Value")]
    public int Val1 { get; set; }

    [Category("Category2")]
    [DisplayName("Value")]
    public int Val2 { get; set; }

    [Category("Category3")]
    [DisplayName("Value")]
    public int Val3 { get; set; }
}

Sure, we're reusing the display name "Value," but since each instance is in a different category, everything should be fine, right? Well; not exactly. Under the hood, the grid determines equality between GridEntrys by comparing the combination of label, property type, and tree depth. And in this case, "label" means display name. So it doesn't matter if the actual code names of the underlying properties differ—as long as their display names, types, and depths are the same, the grid will consider their entries equal. One consequence of this is that if PropertyGrid.Refresh() is called while the Category3 Value is selected, the selection will move to the Category1 Value; presumably because it is the first entry in the tree where .Equals(oldSelection) returns true.

Luckily, there is a workaround. PropertyGrid omits tab characters when it prints display names, so you can simply add a different number of \t's to the beginning or end of each one to make them unique. A bit of a hack to be sure, but it does the job.

Thanks to stackoverflow for assisting me in my investigation of this issue.