Make Grid row/column definitions styleable

[jmacato]

What does the pull request do?

This is a PR for this concept i had in mind for a long time now. Unit tests seems to pass and ControlCatalog/DataGrid works too.

What is the current behavior?

Currently you can't set Grid's Row/ColumnDefinition property in Styles...

What is the updated/expected behavior with this PR?

This enables the user to set those properties in Styles. If combined with pseudoclasses, it can also enable responsive layout too.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?

[MarchingCube]

Can you add unit tests for this?

[grokys]

Seems to work well, however there's a definite problem with the way the properties are implemented, and also we need some unit tests that actually test this working with styles. Close though!

[grokys]

This comment isn't really true any more is it? The value's no longer being clamped.

[grokys]

Putting initialization in the getter for a styled property isn't a good idea because it won't be run when calling e.g. GetValue or GetObservable, for example this fails:

        [Fact]
        public void ColumnDefinitions_Should_Not_Be_Null()
        {
            var grid = new Grid();

            Assert.NotNull(grid.GetValue(Grid.ColumnDefinitionsProperty));
        }

It's not really possible to have lazily-initialized styled properties; you should initialize the properties in the constructor. This is the same in WPF/UWP: https://wpf.2000things.com/2010/11/07/118-dont-add-code-to-dependency-property-gettersetter/

[maxkatz6]

@grokys I don't remember about WPF, but UWP has default value factory in the DependencyProperty
See https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.propertymetadata.createdefaultvaluecallback?view=winrt-19041

It also helps in cases, when default value is mutable - https://devblogs.microsoft.com/oldnewthing/20191002-00/?p=102950

[maxkatz6]

Although it doesn't provide access to dependency object itself as I remember

[grokys]

I've spoken to @jmacato about this PR in private chat and we're running into the problem that collection properties currently cannot be styled due to a limitation of how XAML works.

I've opened an issue to discuss a proposed solution here: #4464

[grokys]

Given that this is very out of date by now, and the feature will need changes in the XAML compiler first, I'm going to close this PR to try to reduce noise in our PR list. We should definitely implement this feature though!

[CollinAlpert]

I hate to be that guy, but any updates on this? Is there anything I could help out with?

[wieslawsoltes]

I hate to be that guy, but any updates on this? Is there anything I could help out with?

If you really need that you can do this workaround using custom control based on Grid (bind to ColumnDefinitionsSource and/or RowDefinitionsSource:

public class BindableGrid : Grid
{
	public static readonly StyledProperty<string?> ColumnDefinitionsSourceProperty =
		AvaloniaProperty.Register<BindableGrid, string?>(nameof(ColumnDefinitionsSource));

	public static readonly StyledProperty<string?> RowDefinitionsSourceProperty =
		AvaloniaProperty.Register<BindableGrid, string?>(nameof(RowDefinitionsSource));

	public BindableGrid()
	{
		InvalidateDefinitions();
	}

	public string? ColumnDefinitionsSource
	{
		get => GetValue(ColumnDefinitionsSourceProperty);
		set => SetValue(ColumnDefinitionsSourceProperty, value);
	}

	public string? RowDefinitionsSource
	{
		get => GetValue(RowDefinitionsSourceProperty);
		set => SetValue(RowDefinitionsSourceProperty, value);
	}

	protected override void OnPropertyChanged<T>(AvaloniaPropertyChangedEventArgs<T> change)
	{
		base.OnPropertyChanged(change);

		if (change.Property == ColumnDefinitionsSourceProperty
			|| change.Property == RowDefinitionsSourceProperty)
		{
			InvalidateDefinitions();
		}
	}

	private void InvalidateDefinitions()
	{
		if (ColumnDefinitionsSource is not null && RowDefinitionsSource is not null)
		{
			var columns = GridLength.ParseLengths(ColumnDefinitionsSource).Select(x => new ColumnDefinition(x));
			ColumnDefinitions.Clear();
			ColumnDefinitions.AddRange(columns);

			var rows = GridLength.ParseLengths(RowDefinitionsSource).Select(x => new RowDefinition(x));
			RowDefinitions.Clear();
			RowDefinitions.AddRange(rows);

			InvalidateMeasure();
			InvalidateArrange();
		}
	}
}

[CollinAlpert]

@wieslawsoltes Thanks for the workaround, however I am trying to modify the ColumnDefinitions in a TimePicker to save some space.

[jmacato]

@CollinAlpert i would really love to revive this but @grokys and I hasnt settled on a final version of this issue #4464 . until then this will not move forward. Which is quite a shame tbh :(

[amwx]

I was looking at some things in MAUI which reminded me of this PR and it seems they have a nice solution for this:

Their BindableProperty.Create function takes an optional delegate for creating a default value, which passes in the reference to the BindableObject for creation, ex from their Grid

public static readonly BindableProperty ColumnDefinitionsProperty = BindableProperty.Create("ColumnDefinitions",
	typeof(ColumnDefinitionCollection), typeof(Grid), null, validateValue: (bindable, value) => value != null,
	propertyChanged: UpdateSizeChangedHandlers, defaultValueCreator: bindable =>
	{
                var colDef = new ColumnDefinitionCollection();
                colDef.ItemSizeChanged += ((Grid)bindable).DefinitionsChanged;
                return colDef;
	});

This is then invoked in BindableObject.GetValue() if necessary. This seems like a pretty straightforward IMO, and shouldn't be to hard to implement as I don't think it would require any big changes to implement and should avoid any issues with priority.