Question

If I try to change a value in a ComboBox‘s Items, it will only actually update if the new value is different from the current value after a case-insensitive compare.

Let’s make a ComboBox with one item:

ComboBox cboBox = new ComboBox();
cboBox.Items.Add("Apple");

The following code will make the ComboBox still show “Apple”, even though the string should look different:

cboBox.Items[0] = "APPLE";

And the naive workaround that I’ve been using, which will make it display correctly:

cboBox.Items[0] = "";
cboBox.Items[0] = "APPLE";

I wanted to figure out how this was happening, so I dug around with a reflector and found this. This is the ComboBox.ObjectCollection.SetItemInternal method that gets called when you try to modify a value:

internal void SetItemInternal(int index, object value)
{
    ...

    this.InnerList[index] = value;
    if (this.owner.IsHandleCreated)
    {
        bool flag = index == this.owner.SelectedIndex;
        if (string.Compare(this.owner.GetItemText(value), this.owner.NativeGetItemText(index), true, CultureInfo.CurrentCulture) != 0)
        {
            this.owner.NativeRemoveAt(index);
            this.owner.NativeInsert(index, value);
            if (flag)
            {
                this.owner.SelectedIndex = index;
                this.owner.UpdateText();
            }
            if (this.owner.AutoCompleteSource == AutoCompleteSource.ListItems)
            {
                this.owner.SetAutoComplete(false, false);
                return;
            }
        }
        else
        {
            if (flag)
            {
                this.owner.OnSelectedItemChanged(EventArgs.Empty);
                this.owner.OnSelectedIndexChanged(EventArgs.Empty);
            }
        }
    }
}

That true in string.Compare is telling it to ignore the case of the string. Why was this method chosen for deciding whether or not to update the value? And why didn’t they expose the case sensitivity?

Is there an alternative way to update an item in an ObjectCollection so that I don’t have to guess whether or not it actually gets updated?

EDIT: I should note that the DropDownStyle is set to DropDownList: this is a read-only ComboBox that occasionally needs to be updated due to actions elsewhere in the program.

Answer 1

After submitting a report to the MSDN, it was marked as “by-design” and nothing more, so that’s that.