Question : How can I get a value to show in a combobox.dropdownlist?

I have a combobox with DropdownStyle=DropdownList but when I set the SelectedIndex to a value programmatically it does not show up on the combobox. The combobox always shows blank as if nothing was selected until I manually select something from the dropdown list. In which case it shows the value selected.

I have been through the code in debug both before and after the combo box has displayed and the SelectedIndex for the combo box is set correctly - yet it refuses to display the text associated with the selection.

Before the combobox was set to be DropDown and I had no problem getting it to display the initial value.

Is there a way around this? Or, do I have to set some flag to get it to display a programmatically set value?

Thanks,

Steve

Answer : How can I get a value to show in a combobox.dropdownlist?

Hi wsprhino;

In the class TileRhombEdgesPanel you set up the comboBox at design time with these values:

//
// lwcbxThinThinWidth
//
this.lwcbxThinThinWidth.BackColor = System.Drawing.SystemColors.Window;
this.lwcbxThinThinWidth.DropDownWidth = 70;
this.lwcbxThinThinWidth.Font = new System.Drawing.Font("Microsoft Sans Serif", 9F);
this.lwcbxThinThinWidth.FormattingEnabled = true;
this.lwcbxThinThinWidth.Items.AddRange(new object[] {
"Narrow",
"Normal",
"Wide",
"Extra Wide"});
this.lwcbxThinThinWidth.Location = new System.Drawing.Point(62, 19);
this.lwcbxThinThinWidth.Name = "lwcbxThinThinWidth";
this.lwcbxThinThinWidth.Size = new System.Drawing.Size(85, 23);
this.lwcbxThinThinWidth.TabIndex = 334;

Then just before the form is displayed to the user the system calls the class LineWidthComboBox OnCreateControl which does the following:

base.OnCreateControl();

this.BeginUpdate();
this.Items.Clear();
this.Items.Add("Narrow");
this.Items.Add("Normal");
this.Items.Add("Wide");
this.Items.Add("Extra Wide");
this.EndUpdate();

this.Size  = new Size(85, 24);
this.Font  = new Font("Microsoft San Serif", 9.00f, FontStyle.Regular);

The first thing you do after the BeginUpdate call is to clear all the values from the dropdown list and then re-populate the drop down values then re-sets the SelectedIndex to -1, no selection. If you comment out the code from the BeginUpdate to the EndUpdate then the combo box will display correctly.

Another thing in this same code is that the InitializeComponent never gets called because there is no call to it in the constructor.

In the code file Program.cs you have this:

           Application.EnableVisualStyles();
           Application.SetCompatibleTextRenderingDefault(false);

           TileRhombEdgesForm tref = new TileRhombEdgesForm();
           tref.ThinThinEdgeWidth = LineWidth.LineWidthValue.Wide;

           Application.Run(tref);

Anything you do to the TileRhombEdgesForm class before the call to Application.Run that will cause an event to be triggered will not occurr because the Application.Run is where the windows message loop gets started. Any changes to the class should be done in the constructor.

Fernando