Drop-down opening of RadMultiColumnComboBox delays, when the AutoSizeDropDownToBestFit property is enabled and the control is bound to more than 2000 records. Work around: this.radMultiColumnComboBox1.ValueMember = "ID"; this.radMultiColumnComboBox1.DisplayMember = "Name"; this.radMultiColumnComboBox1.DataSource = table; this.radMultiColumnComboBox1.AutoSizeDropDownToBestFit = false; this.radMultiColumnComboBox1.BestFitColumns(true, false);
The reason for the delay is that by default the auto size functionality will measure all cells in the grid in order to determine the drop down size. Hence the more records (rows) you have with more cells in each row, the longer the measure operation would take. To handle this case, we exposed the AutoSizeDropDownColumnMode property. It allows you to switch from measuring all the cells to measuring some subset of cells that will work for you i.e. the DisplayedCells option will measure only with the currently visible cells. Here is a code snippet: this.radMultiColumnComboBox1.AutoSizeDropDownToBestFit = true; this.radMultiColumnComboBox1.AutoSizeDropDownColumnMode = Telerik.WinControls.UI.BestFitColumnMode.DisplayedCells;