Make WPF/SL grid ignore a child element when determining size

Question

I have a Grid which has several children, one of which is a ScrollViewer. I want the Grid to size itself based on all of its children except the ScrollViewer, which

Answer 1

Pavlo Glazkov's answer works very well for me! I have used it for a control that does not want to specify explicit sizes ... I added some logic and properties to defeat one dimension:

public sealed class NoSizeDecorator
            : Decorator
    {
        /// 

        /// Sets whether the width will be overridden.
        /// 
        public static readonly DependencyProperty DisableWidthOverrideProperty
                = DependencyProperty.Register(
                        nameof(NoSizeDecorator.DisableWidthOverride),
                        typeof(bool),
                        typeof(NoSizeDecorator),
                        new FrameworkPropertyMetadata(
                                false,
                                FrameworkPropertyMetadataOptions.AffectsMeasure));

        /// 

        /// Sets whether the width will be overridden.
        /// 
        public bool DisableWidthOverride
        {
            get => (bool)GetValue(NoSizeDecorator.DisableWidthOverrideProperty);
            set => SetValue(NoSizeDecorator.DisableWidthOverrideProperty, value);
        }

        /// 

        /// Sets whether the height will be overridden.
        /// 
        public static readonly DependencyProperty DisableHeightOverrideProperty
                = DependencyProperty.Register(
                        nameof(NoSizeDecorator.DisableHeightOverride),
                        typeof(bool),
                        typeof(NoSizeDecorator),
                        new FrameworkPropertyMetadata(
                                false,
                                FrameworkPropertyMetadataOptions.AffectsMeasure));

        /// 

        /// Sets whether the height will be overridden.
        /// 
        public bool DisableHeightOverride
        {
            get => (bool)GetValue(NoSizeDecorator.DisableHeightOverrideProperty);
            set => SetValue(NoSizeDecorator.DisableHeightOverrideProperty, value);
        }


        protected override Size MeasureOverride(Size constraint)
        {
            UIElement child = Child;
            if (child == null)
                return new Size();
            constraint
                    = new Size(
                            DisableWidthOverride
                                    ? constraint.Width
                                    : 0D,
                            DisableHeightOverride
                                    ? constraint.Height
                                    : 0D);
            child.Measure(constraint);
            return new Size(
                    DisableWidthOverride
                            ? child.DesiredSize.Width
                            : 0D,
                    DisableHeightOverride
                            ? child.DesiredSize.Height
                            : 0D);
        }
    }