We need more information on the SelfSizingDelegate

[rmarinho]

What i m missing is a MeasureMode,

MeasureMode
{
   Undefined,
   Exactly,
   AtMost
}

Undefined is - ok i don’t have any constrain use the max value you want,: MeasureMode AtMost - says take this constrain (parent size), measure yourself on it and try to be the min size you want , and MeasureMode.Exact is ok please use the size i gave to you .. for example in Stretch mode ..

void HandleSelfSizingDelegate(Xamarin.Flex.Item item, ref float width, ref float height) 
{
    var widthMode = FlexMeasureMode.Undefined;
    var heightMode = FlexMeasureMode.Undefined;

    var availableWidth = item.Parent.Width;
    var availableHeight = item.Parent.Height;
    var size = _measure?.Invoke(item as IFlexNode, availableWidth, widthMode, availableHeight, heightMode);
    width = (float)size.Value.Width;
    height = (float)size.Value.Height;
}

Here's my code on the Xamarin.Forms side of things

Size MeasureView(IFlexNode node, float width, FlexMeasureMode widthMode, float height, FlexMeasureMode heightMode)
{
    var constrainedWidth = (widthMode == FlexMeasureMode.Undefined) ? float.MaxValue : width;
    var constrainedHeight = (heightMode == FlexMeasureMode.Undefined) ? float.MaxValue : height;

    View view = node.Data as View;

    var sizeRequest = view.Measure(constrainedWidth, constrainedHeight);

    var sizeThatFitsWidth = (float)sizeRequest.Request.Width;
    var sizeThatFitsHeight = (float)sizeRequest.Request.Height;

    var finalWidth = SanitizeMeasurement(constrainedWidth, sizeThatFitsWidth, widthMode);
    var finalHeight = SanitizeMeasurement(constrainedHeight, sizeThatFitsHeight, heightMode);

    return new Size(finalWidth, finalHeight);
}

static float SanitizeMeasurement(float constrainedSize, float measuredSize, FlexMeasureMode measureMode)
{
    float result;
    if (measureMode == FlexMeasureMode.Exactly)
    {
        result = constrainedSize;
    }
        else if (measureMode == FlexMeasureMode.AtMost)
    {
        result = Math.Min(constrainedSize, measuredSize);
    }
    else
    {
        result = measuredSize;
    }

    return result;
}

[lrz]

Closing per prior discussion, we will instead introduce per-case fixes.