[MAC] Expander with visual bug due to animation sizing

[bow-meow]

Expected Behavior

Having an expander set as the content of a panel with no size limitations should just work.
You should be able to expand/collapse the control with no visual errors.

Actual Behavior

Doing the above will cause the header to gain in size once exiting its collapsed state to expanded.

Steps to Reproduce the Problem

I have managed to reproduce this in your test app in the 'ExpanderSection' with only one line of code at the bottom of the ctor

public ExpanderSection()
{
    var expandedCheckBox = new CheckBox { Text = "Expanded" };
    var enabledCheckBox = new CheckBox { Text = "Enabled" };

    var expander = new Expander
    {
    Header = "Test Header",
    Content = new Panel { Size = new Size(200, 200), BackgroundColor = Colors.Blue }
    };

    expandedCheckBox.CheckedBinding.Bind(expander, e => e.Expanded);
    enabledCheckBox.CheckedBinding.Bind(expander, e => e.Enabled);

    LogEvents(expander);

    var expander2 = new Expander
    {
        Header = new StackLayout
    {
        Orientation = Orientation.Horizontal,
        Items = { "Test Expanded with custom header", new TextBox() }
    },
        Expanded = true,
        Content = new Panel { Size = new Size(300, 200), BackgroundColor = Colors.Blue }
    };

    LogEvents(expander2);

    Content = new StackLayout
    {
        Padding = new Padding(10),
        Items =
        {
            new StackLayout 
            {
                Orientation = Orientation.Horizontal,
                Items =
                {
                    expandedCheckBox,
                    enabledCheckBox
                }
            },
            expander,
            expander2
        }
    };

    Content = expander2; <----------this is the only line I added to make this bug happen
}

My Thoughts

I believe this is to do with the animation sizing code in the ExpanderHandler, in the method 'UpdateExpandedState', because when the 'EnableAnimation' is set to false, this visual bug no longer occures. It could be to do with something else though, not totally sure, this is just what I observed ( :

Specifications

• Version: latest
• Platform(s): Mac, XamMac
• Operating System(s): macOS 10.13

[cwensley]

Hey @bow-meow, thanks for reporting the issue!