How to get the DisplayMember value in the DrawItem event of a comboBox? C#

Question

Please consider the following:

I populate my comboBox using the following method:

void populateComboBox()
{
    comboBox1.DataSource = GetDataTableSource(); // some data table used as source
    comboBox1.DisplayMember = "name";            // string
    comboBox1.ValueMember = "id";                // id is an int

    // Suppose I have this data in my comboBox after populating it
    // 
    //
    // id (ValueMember) | name (DisplayMember)
    // -----------------------------------------
    //  1       | name1
    //  2       | name2
    //  3       | name3
}

In DrawItem event, I want to get the value of the DisplayMember (name) of the comboBox and assign it to some variable. So far, I got this code and it seems not to work... Please have it corrected. Thanks in advance....

void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
{
    string name = ((System.Data.DataRowView)(comboBox1.SelectedValue = e.Index))["name"].ToString();

    // do something
    //  
}

Answer 1

Ok, i just came across this problem myself and here is an even better answer:

string displayValue = this.GetItemText(this.Items[e.Index]);             
g.DrawString(displayValue, e.Font, br, e.Bounds.Left, y + 1);

Per MSDN:

If the DisplayMember property is not specified, the value returned by GetItemText is the value of the item's ToString method. Otherwise, the method returns the string value of the member specified in the DisplayMember property for the object specified in the item parameter

http://msdn.microsoft.com/en-us/library/system.windows.forms.listcontrol.getitemtext(v=vs.80).aspx

Answer 2

how about using just combobox item, it is selected displayed value:

string name = (string)comboBox1.Items[e.Index];

If you getting e.Index = -1, change DrawMode = OwnerDrawVariable and DropDownStyle = DropDown

EDIT:

Ok I understood whats wrong. I tested with strings as datasource, so in your code should work this:

string name = ((DataRowView)comboBox1.Items[e.Index])["name"];

Answer 3

If you want to make a really generic function you could elaborate a bit:

Lets say you have two comboboxes, one containing items based of custom collection A with DisplayMember AA and the other contains items based on custom collection B with DisplayMember BB:

How could a generic function know which value to return? Based of DisplayMember of course, but you don't want to pass AA / BB to a generic function if you want it generic.

So

[anItemTheCombobox.GetType().GetProperty(theCombobox.DisplayMember).GetValue(theCombobox, null)];

Background

I used it in a generic function called calculateAndSetWidth. The function loops through all items in listbox to determine the maxWidth:

public void calculateAndSetWidth(ListBox listbox, int minWidth = 0) {
Graphics graphics = this.CreateGraphics();
int maxWidth = 0;
SizeF mySize = null;

foreach (object item in listbox.Items) {
    mySize = graphics.MeasureString(item.GetType().GetProperty(listbox.DisplayMember).GetValue(item, null), listbox.Font);
    if (mySize.Width > maxWidth) {
        maxWidth = mySize.Width;
    }
}

listbox.Width = Math.Max(maxWidth, minWidth);

}