[BUG] MAUI Toolkit Converters Not Triggering for ObservableCollection Property changes.

[divyesh008]

Is there an existing issue for this?

• I have searched the existing issues

Did you read the "Reporting a bug" section on Contributing file?

• I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

Current Behavior

I have created a custom control using the CollectionView that includes a floating "Add" button. The visibility of this button depends on two conditions:

1. The AttachmentList should contain data.
2. The IsEditable property should be set to true.

To implement this, I used the following .NET MAUI Toolkit converters:

• IsMultiValueAllTrueConverter
• IsListNotNullOrNotEmptyConverter

The Button visibility is bound using a MultiBinding as shown below:

<Button
    Grid.Row="0"
    Text="Add"
    -----
    VerticalOptions="End">
    <Button.IsVisible>
         <MultiBinding Converter="{StaticResource IsMultiValueAllTrueConverter}">
            <Binding
                Path="Attachments"
                Converter="{StaticResource IsListNotNullOrNotEmptyConverter}"/>
            <Binding Path="IsEditable"/>
        </MultiBinding>
    </Button.IsVisible>
</Button>

Issue:

When deleting all items from the AttachmentList, the converters are not triggered, and the floating "Add" button remains visible, even though the list is empty. Despite implementing INotifyPropertyChanged for AttachmentList manually, the behavior persists.

Workaround:

To resolve the issue temporarily, I introduced a new bindable property, HasData, which is a boolean. Its value is updated during data loading and deletion actions. This property is then used in the MultiBinding, and the visibility logic works as expected:

<Button
    Grid.Row="0"
    Text="Add"
    -----
    VerticalOptions="End">
    <Button.IsVisible>
        <MultiBinding Converter="{StaticResource IsMultiValueAllTrueConverter}">
            <Binding Path="HasData"/>
            <Binding Path="IsEditable"/>
        </MultiBinding>
    </Button.IsVisible>
</Button>

Expected Behavior

The IsMultiValueAllTrueConverter and IsListNotNullOrNotEmptyConverter must handle changes in any ObservableCollection accurately. Specifically, they should respond to Add and Delete operations within the collection.

Steps To Reproduce

• Load a list of attachments in the AttachmentList property using ToggleData.
• Click Toggle Edit Mode button to get the floating Add button
• Delete all the items from the list.
• Observe that the "Add" button remains visible, even though the list is empty.

The.issue.mov

Link to public reproduction project repository

https://github.com/divyesh008/Converters_bug.git

Environment

- .NET MAUI CommunityToolkit: 9.0.3, 11.0.0
- OS: Macos 16.0, Windows Build 10.0.19041.0
- .NET MAUI: 9.0.0/9.0.100

Anything else?

Request:

Please investigate this and provide a fix or guidance for a more robust solution.

[TheCodeTraveler]

Be sure to manually assign Behavior.BindingContext.

More information is available in the release notes: https://github.com/CommunityToolkit/Maui/releases/tag/10.0.0

Additional information available on StackOverflow: https://stackoverflow.com/a/79099574/5953643

[divyesh008]

@brminnick The issue is not related to behavior but rather to the ObservableCollection property changes not being tracked by the .NET MAUI Toolkit converter. In other words, the changes in the ObservableCollection are not being properly notified or observed by the converter.

[bijington]

@divyesh008 the converter should not subscribe to any events on the ObservableCollection in order to monitor changes inside the collection because there is no lifecycle to know when to unsubscribe from the events. If you want to achieve something like this I would recommend either writing the code behind in your control or creating something like a Behavior to solve your issue.

[Divyesh-Bhatt]

Thank you for your feedback. I appreciate your concerns about subscribing to events on the ObservableCollection and the potential lifecycle challenges this approach might introduce. While handling changes via the OnPropertyChanged method in the code-behind is certainly an option, the primary advantage of using an ObservableCollection lies in its ability to automatically notify changes. This is particularly beneficial when working with controls such as CollectionView, ListView, or BindableStackLayout, which rely on these notifications to reflect updates dynamically and maintain seamless functionality.

The IsListNotNullOrEmptyConverter has been specifically designed to work with these controls. As such, whenever the ItemSource property becomes null or empty, the converter should trigger automatically to reflect the updated state.

, but that still looks odd to me that why converters are not getting notified

If there are alternative approaches or suggestions to improve the implementation while maintaining this functionality, I would be happy to consider them. Please let me know your thoughts.

[stephenquan]

I think there's a typo and the list converter is named IsListNotNullOrEmptyConverter and not IsListNotNullOrNotEmptyConverter.

Your problem could be solved if you were to bind to Attachments.Count and IsEditable.

As an example of this, I use the MultiMathExpressionConverter with an appropriate expression.

<Button
    Grid.Row="0"
    IsVisible="{MultiBinding {Binding Attachments.Count},
                             {Binding IsEditable},
                             Converter={StaticResource MultiMathExpressionConverter},
                             ConverterParameter='!! x0 and x1'}"
    Text="Add"
    VerticalOptions="End" />

[divyesh008]

Thanks for the suggestion, I've tried it but this did not worked.

[stephenquan]

I see there were two reasons why it may have now worked. (1) I got the expression wrong, I have now corrected it to read !! x0 and x1, (2) I forgot to state that it requires CommunityToolkit.Maui versions 11.0.0 for it to work.

Another expression that may have been easier to read is:

                <Button
                    Grid.Row="0"
                    IsVisible="{MultiBinding {Binding Attachments.Count},
                                             {Binding IsEditable},
                                             Converter={StaticResource MultiMathExpressionConverter},
                                             ConverterParameter='( x0 gt 0 ) and x1'}"
                    Text="Add"
                    VerticalOptions="End" />

[divyesh008]

I'm able to handle this using

<Button.IsVisible>
    <MultiBinding Converter="{StaticResource IsMultiValueAllTrueConverter}">
        <Binding Path="Attachments.Count" Converter="{StaticResource IntToBoolConverter}"/>
        <Binding Path="IsEditable" />
    </MultiBinding>
</Button.IsVisible>