Modifying original DataSource doesn't update ComboBox

Question

I have a ComboBox with a DataSource set to application settings as follows

public DetailsForm()
{
    InitializeComponent();
    this.comboBox1.DataSource = TextSelectionSettings.Default.categories;
}

But I want users to add extra items to the combo box if they need to at runtime. So I just made a simple click event on a textbox to test adding a new string to the list.

private void textBox1_MouseClick(object sender, MouseEventArgs e)
{
    TextSelectionSettings.Default.categories.Add("test");
    TextSelectionSettings.Default.Save();
}

However the ComboBox doesn't show the new string I added to the settings.

How can I refresh the ComboBox to show the changes in the settings?

Refresh() function on the combo box did not work.
setting the DataSource again did not work either.
I cannot add the Item directly to ComboBox using Items.Add() method because the DataSource is set.

In order for it to pick up on the change it must implement `INotifyPropertyChanged` or `INotifyCollectionChanged`. Try setting the `DataSource = null` and then set it again. — Ron Beyer, Apr 05 '18 at 21:08
@RonBeyer setting DataSource to null and then back again to the categories worked, thank you — erotavlas, Apr 05 '18 at 21:10

Ron Beyer · Accepted Answer · 2018-04-05T21:23:00.553

5

In order for the Data Bindings in Windows Forms (and WPF) to work, it has to have some kind of change-notification like IBindingList or INotifyCollectionChanged to be able to notice the changes.

Calling Refresh() is simply for painting and doesn't refresh the bindings
Setting the .DataSource to the same thing won't work (you don't change anything, so it doesn't notice it as a change)

The work-around is to set the .DataSource to null and then set it back to the collection again. This causes it to re-evaluate the binding (because it is a different object than the current null one) and reset your values.

edited Apr 05 '18 at 21:23

answered Apr 05 '18 at 21:13

Ron Beyer

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`INotifyPropertyChanged` is completely irrelevant to the problem. Relevant interface for this problem (receiving `ListChanged` notifications) is `IBindingLust` as described in the [linked post](https://stackoverflow.com/a/33625054/3110834). – Reza Aghaei Apr 05 '18 at 21:22
@RezaAghaei I removed it, although for other Data bindings `INotifyPropertyChanged` would be relevant to data binding (things like Textbox), but yes, not relevant in this scenario. – Ron Beyer Apr 05 '18 at 21:24

Modifying original DataSource doesn't update ComboBox

1 Answers1