Combobox selected item value set null in datagrid when the tab change

[Nikhilthambi]

Describe the bug I have a Datagrid and inside this Datagrid there is one Combobox. When I switch the tab the Combobox SelectedItem is empty automatically without any action.

To Reproduce Steps to reproduce the behavior:

1. Create 2 tabs
2. Inside one tab create a Datagrid and fill the cells one cell should be Combobox with list and selectedItem
3. Switch the tab and come back to Datagrid tab
4. You can see the selectedItem will be empty

Expected behavior To have the combobox retain their values after switching tabs (When change the Tab somehow the SelectedItem property value is set to null. This should not happen)

Screenshots Before switching tabs:

After switching tab:

Desktop (please complete the following information):

• OS: Windows 10
• Avalonia Version 0.10.19

Additional context there is already a closed ticket same scenario like this but the issue is still there. Please find the related closed bug ticket: https://github.com/AvaloniaUI/Avalonia/issues/5661

Could you please check and fix this issue?

Thanks

[timunie]

is the ComboBox bound to anything in the ViewModel?

[Nikhilthambi]

yes the value bound in the viewmodel.

[timunie]

In that case that shouldn't happen. However, current supported version is 11.0.4, so unlikely a bug in v0.10 gets fixed. I see two options for now:

1. Enable compiled bindings (if not yet) to debug binding issues better. If that doesn't help,
2. try DataGridTemplateColumn

[ykarpeev]

I am seeing an issue that I think is related. Selected item in combobox is null - if I scroll in my datagrid or resize the window then the combox selected value value shows up. This is with 11.0.4.

and after manipulating window size a few times.

I'll try to look into it here to see if I can find anything.

[timunie]

@ykarpeev please file a minimal sample to reproduce.

[Nikhilthambi]

I am seeing an issue that I think is related. Selected item in combobox is null - if I scroll in my datagrid or resize the window then the combox selected value value shows up. This is with 11.0.4.

and after manipulating window size a few times.

I'll try to look into it here to see if I can find anything.

I am also getting something similar issue, my case when I switch the tab and I tried with this 11.0.2 version.

[Nikhilthambi]

In that case that shouldn't happen. However, current supported version is 11.0.4, so unlikely a bug in v0.10 gets fixed. I see two options for now:

1. Enable compiled bindings (if not yet) to debug binding issues better. If that doesn't help,
2. try DataGridTemplateColumn

I tried both solution but still getting the same issue

[timunie]

@Nikhilthambi if you have a minimal sample to reproduce, please share it.

[ykarpeev]

Here is a minimal sample.

https://github.com/ykarpeev/avaloniadatagridrepro

For me, on resizing the window to a few pixels wide then resizing back a couple of times will make some of the selected items show up.

[ykarpeev]

https://github.com/AvaloniaUI/Avalonia/assets/6986975/92dbca59-f018-4dbd-bb43-49966e9a9375

[timunie]

@ykarpeev found your issue. You are binding to $parent[] but DataGridColumn cannot resolve it. So better to bind to named element here. Set x:Name to the window or DataGrid and bind to it via #root.DataContext...

Sent a PR: https://github.com/ykarpeev/avaloniadatagridrepro/pull/1

[ykarpeev]

Thank you. That solves part of my issue, but I think mine must be separate from the parent and is related to the fact that my datagrid is in a user control. If they are using a usercontrol maybe it is still the same.

Switching between tabs I see new errors

Binding]Error in binding to 'datagridrepro.Views.UserControl1'.'DataContext': 'Null value in expression '{empty}' at ''.'(UserControl1 #33189039) [Binding]Error in binding to 'Avalonia.Controls.ComboBox'.'ItemsSource': 'Null value in expression '{empty}' at '$parent[UserControl, 0].DataContext'.'(ComboBox #50685404) [Binding]Error in binding to 'Avalonia.Controls.ComboBox'.'ItemsSource': 'Null value in expression '{empty}' at '$parent[UserControl, 0].DataContext'.'(ComboBox #41270904) [Binding]Error in binding to 'Avalonia.Controls.ComboBox'.'ItemsSource': 'Null value in expression '{empty}' at '$parent[UserControl, 0].DataContext'.'(ComboBox #51461341)

https://github.com/AvaloniaUI/Avalonia/assets/6986975/178aee8a-ce9c-4ead-881a-c1826b129013

[ykarpeev]

I fixed this by wrapping the usercontrol in a contentcontrol..

        _<ContentControl>
            <local:UserControl1 DataContext="{Binding}" />
        </ContentControl>_

[timunie]

@ykarpeev you can also give the DataGrid or UserControl or whatever a name and use the same strategy.