How to maintain ComboBox.SelectedItem reference when DataSource is resorted?
- by Dave
This really seems like a bug to me, but perhaps some databinding gurus can enlighten me? (My WinForms databinding knowledge is quite limited.)
I have a ComboBox bound to a sorted DataView. When the properties of the items in the DataView change such that items are resorted, the SelectedItem in my ComboBox does not keep in-sync. It seems to point to someplace completely random. Is this a bug, or am I missing something in my databinding?
Here is a sample application that reproduces the problem. All you need is a Button and a ComboBox:
public partial class Form1 : Form
{
private DataTable myData;
public Form1()
{
this.InitializeComponent();
this.myData = new DataTable();
this.myData.Columns.Add("ID", typeof(int));
this.myData.Columns.Add("Name", typeof(string));
this.myData.Columns.Add("LastModified", typeof(DateTime));
this.myData.Rows.Add(1, "first", DateTime.Now.AddMinutes(-2));
this.myData.Rows.Add(2, "second", DateTime.Now.AddMinutes(-1));
this.myData.Rows.Add(3, "third", DateTime.Now);
this.myData.DefaultView.Sort = "LastModified DESC";
this.comboBox1.DataSource = this.myData.DefaultView;
this.comboBox1.ValueMember = "ID";
this.comboBox1.DisplayMember = "Name";
}
private void saveStuffButton_Click(object sender, EventArgs e)
{
DataRowView preUpdateSelectedItem = (DataRowView)this.comboBox1.SelectedItem;
// OUTPUT: SelectedIndex = 0; SelectedItem.Name = third
Debug.WriteLine(string.Format("SelectedIndex = {0:N0}; SelectedItem.Name = {1}", this.comboBox1.SelectedIndex, preUpdateSelectedItem["Name"]));
this.myData.Rows[0]["LastModified"] = DateTime.Now;
DataRowView postUpdateSelectedItem = (DataRowView)this.comboBox1.SelectedItem;
// OUTPUT: SelectedIndex = 2; SelectedItem.Name = second
Debug.WriteLine(string.Format("SelectedIndex = {0:N0}; SelectedItem.Name = {1}", this.comboBox1.SelectedIndex, postUpdateSelectedItem["Name"]));
// FAIL!
Debug.Assert(object.ReferenceEquals(preUpdateSelectedItem, postUpdateSelectedItem));
}
}
