Xamarin MultiBinding Needs BindingContext from higher ancestor level or named Items in XAML tree

Question

I am Building a rectangular Grid of Homogeneous Buttons with Dynamic Rows and Columns to Be set at Runtime. The Code is in Xamarin. All the latest versions etc. Entire Project can be Downloaded here: https://github.com/BicycleMark/XamSweeper The Problem I am having is the MultiBinding Portion of the XAML. Any review or suggestions would be super-excellent

I used Nested StackPanels to create the Grid like this:

I succeeded at creating a MultiValueConverter for sizing the Buttons which are appearing correctly. I have Tested the Converter with a Unit Test and it functions as Expected. the [R,C] is printed in the Test of each Button. These are pulled from Model which is bound Correctly

The problem I am having is in Linking the MultiBinding to 3 Items I need to calculate Size for the Buttons:

The Width of Each Button is calculated with these three parameters

ActualWidth of Frame Holding the Buttons
Number of Columns Of Buttons Of Model
Spacing or Padding between each Button
If any [1..3] are null return 50 <--- This is What I return because my Binding is not working

The Height of Each Button is calculated with these three parameters

ActualHeight of Frame Holding the Buttons
Number of Rows Of Buttons Of Model
Spacing or Padding between each Button
If any [1..3] are null return 50 <--- This is What I return because my Binding is not working

Here is the Converter Described:

    public class SizeConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        if (values == null || values.Length <3 || values[2] == null || values[1] == null || values[0] == null)
            return 50;
        int numItems = (int)values[2];
        int separatorSize = (int)values[1]; 
        double frameSize = System.Convert.ToDouble(values[0]) ;
        
        int totalSeparatorSize = (numItems - 1) * separatorSize;
        int remainingArea = System.Convert.ToInt32(frameSize) - totalSeparatorSize;
        return remainingArea / numItems;
    }
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And Its Unit Test Which Passes:

 [DataRow(100, 2, 4)]
    [DataTestMethod]
    public void Test_Piece_Sizing(double frameSize, int separatorSize, int numItems)
    {
        var sizeConverter = new SizeConverter();
        object[] values = new object[] { frameSize, separatorSize, numItems };
        Assert.AreNotEqual(0,sizeConverter.Convert(values, typeof(int), null, System.Globalization.CultureInfo.CurrentCulture));
    }

The issue at hand is when I bind My Values in Xamarin My Converter gets Null passed from my XAML Here is the XAML

The Converter is Getting Called but I am passing 3 nulls each time. This is the Binding Error I am trying to repair

Entire Project can be Downloaded here: https://github.com/BicycleMark/XamSweeper

Leo Zhu · Accepted Answer

The Converter is Getting Called but I am passing 3 nulls each time.

You could try to set the BindingContext to the Frame like:

then you could get the value in your Converter.

But ActualWidth seems not be an existing bindable property.

Xamarin MultiBinding Needs BindingContext from higher ancestor level or named Items in XAML tree

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