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misterPhyrePhox

[.net] ListBox.DataSource not updating?

6 posts in this topic

In my WinForms application, I have a ListBox bound to a list using the DataSource property. The problem is that when I update my DataSource indirectly (by modifying my reference to the list), the ListBox does not update to reflect the changes. I've tried Update()ing the ListBox and Refresh()ing the ListBox, but that does nothing. I even tried deriving and calling the RefreshItems() protected member, which sometimes works, but sometimes when I do that the program crashes saying that I have accessed corrupted memory (in C#? who would've thought). I think the way to update the ListBox might have something to do with the protected DataManager member, but I don't know how to use that. Does anyone know how to solve my problem?
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Try this:

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
List<KeyValuePair<int, string>> data = new List<KeyValuePair<int, string>>();

KeyValuePair<int, string> item;

for (int i = 1; i < 10; i++)
{
item = new KeyValuePair<int, string>(i, "Item " + i.ToString());
data.Add(item);

}

listBox1.DataSource = data;
listBox1.DisplayMember = "Value";
listBox1.ValueMember = "Key";

}

private void button1_Click(object sender, EventArgs e)
{
KeyValuePair<int, string> item = new KeyValuePair<int,string>(11,"Item 11");

List<KeyValuePair<int, string>> data = (List<KeyValuePair<int, string>>)listBox1.DataSource;
data.Add(item);

listBox1.DataSource = null;
listBox1.DataSource = data;

}
}

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Quote:
Original post by Machaira
Try this:
*** Source Snippet Removed ***


Thanks, that seems to work. But is there any simple function that can just make the DataSource update? Your way seems a little hackey, and it also destroys the user's selection (although I guess you could store SelectedIndex before reseting the DataSource and then reset SelectedIndex).
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I've had the same problem myself before, and the solution is actually quite simple, it's just not immediately obvious because you have to recast the appropriate object before you get the method you want.

((CurrencyManager)myListBox.BindingContext).Refresh();

That's the one line bit of code to refresh your listbox with new data from the DataSource. Alternatively, you can create a CurrencyManager variable, casted from myListBox.BindingContext, but you only really need to do that if you're going to be using the CurrencyManager for something else too.

Another rather different solution is to use a BindingList as the data source. This automatically fires events and updates the DataSource whenever an item is added/removed/editted.

Hope this helps... :)
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I thought there was a way to rebind, but couldn't remember nor find it in the two minutes I had to whip that up. [sad] Glad someone was here to pick up my slack. [wink]
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Quote:
Original post by alex_myrpg
I've had the same problem myself before, and the solution is actually quite simple, it's just not immediately obvious because you have to recast the appropriate object before you get the method you want.

((CurrencyManager)myListBox.BindingContext).Refresh();

That's the one line bit of code to refresh your listbox with new data from the DataSource. Alternatively, you can create a CurrencyManager variable, casted from myListBox.BindingContext, but you only really need to do that if you're going to be using the CurrencyManager for something else too.

Another rather different solution is to use a BindingList as the data source. This automatically fires events and updates the DataSource whenever an item is added/removed/editted.

Hope this helps... :)


Ah thanks alot!
I actually did ((CurrencyManager)listBox.BindingContext[listBox.DataSource]).Refresh(); -- BindingContext appears to be a collection of BindingManagerBases.
Thanks to both of you for your help.
A final question: does anyone know an article on msdn or elsewhere explaining the basics of data binding in a readable manner?
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Ah, my slight mistake there. That's what happens when I type the code out directly here without testing it, but I'm glad you found the solution easily from there.

Here's your MSDN article (at least the most appropriate one I could find): http://msdn2.microsoft.com/en-us/library/ef2xyb33(vs.80).aspx

Good luck...
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