Question

Error: Index was out of range Must be non-negative and less than the size of the collection

I have a customized LookUpEdit –

public class MyLookUpEdit : LookUpEdit

I refer to the following link to add MyLookUpEdit to a ribbon. Now MyLookUpEdit is available in my ribbonPageGroup–>Add Editor.

http://www.devexpress.com/Support/Center/KB/ViewKBIssue.aspx?kbid=A1237

Here is the InitializeControl Method for MyLookUpEdit:

public void InitializeControl(ICollection cache, string columnField1, string columnField2, string valueField, bool isMultiColumn, int searchColumn)
        {
            Properties.ForceInitialize();
            const int maxDropDownSize = 7;
            Properties.Columns.Clear();

        if(isMultiColumn)
        {
                Properties.Columns.AddRange(new[] {
                new LookUpColumnInfo(columnField1, columnField1, columnField1.Length*6, FormatType.None, "", true, HorzAlignment.Near, DevExpress.Data.ColumnSortOrder.None),
                new LookUpColumnInfo(columnField2, columnField2, 100, FormatType.None, "", true , HorzAlignment.Near, DevExpress.Data.ColumnSortOrder.None)});
                Properties.ShowHeader = true;
                Properties.PopupFormMinSize = new Size(0, 0);
                Properties.AppearanceDropDownHeader.TextOptions.HAlignment = HorzAlignment.Near;
                Properties.AutoSearchColumnIndex = searchColumn;
        }
        else
        {
                Properties.Columns.AddRange(new[]{
                new LookUpColumnInfo(columnField1, columnField1, 10, FormatType.None, "", true, HorzAlignment.Near, DevExpress.Data.ColumnSortOrder.None),
                new LookUpColumnInfo(columnField2, columnField2, 0, FormatType.None, "", false , HorzAlignment.Near, DevExpress.Data.ColumnSortOrder.None)});
                Properties.ShowHeader = false;
                Properties.PopupFormMinSize = new Size(10, 10); // set popup width to control width

                break;
        }

        Properties.ShowFooter = false;
        Properties.ShowLines = true;
        Properties.ValueMember = valueField;
        Properties.DisplayMember = columnField1;
        Properties.DataSource = cache;
        if (cache == null) return;
        Properties.DropDownRows = cache.Count > maxDropDownSize ? maxDropDownSize : cache.Count;

        ColumnBestFit();
        HideIcon();
    }

But at the run time, in ribbon, I cannot click the button and see all available values for the lookupedit – it looks like the popup is not open, and when I leave the edit, the following code throw the error:

    protected override void OnLeave(EventArgs e)
    {
        if (IsPopupOpen) 
        {
            ItemIndex = PopupForm.SelectedIndex;
            _selectfromPopup = true;
        }
    Properties.DisplayMember = Properties.Columns[0].Caption; // This line throw the error

        base.OnLeave(e);

        if (textChanged)
            OnLeaveWithChangedText(e);

    }

Answer 1

there could be different reasons why the columns list is empty, it depends on the whole form events and methods chain and whatsoever, but to be sure and use a defensive approach (my swiss army knife 😉 )

just put a check before:

Properties.DisplayMember = Properties.Columns[0].Caption;

so to execute that row only if the Properties.Columns.Length > 0

this won’t solve everything but as I understand it right now, will prevent that exception and your code will keep running (but eventually not really doing exactly what you expect from it if the error is somewhere else in the fact that list should not be empty).