update_layout.md

Updating the Layout

Updating the On-screen Layout

There are many things that can be done programatically to a layout that might require it to be recalculated and updated on screen. XibFree deliberately provides no support for automatically updating the layout in response to such changes - this is by design, and based on the fact that there are things outside of XibFree's scope that can affect layout.

That said, invoking XibFree to update itself it trivial - simply call the standard iOS method SetNeedsUpdate() on the UILayoutHost view.

Say for example you update the text of a label that has an AutoSize.WrapContent dimension, you would need something like this:

_label.Text = "New text that may cause the layout to change";
_layoutHost.SetNeedsLayout();

Navigation Extensions

XibFree provides a number of UIView extension methods that help navigate between the UIView hierarchy and XibFree's layout tree.

• GetNativeView() - retrieves the NativeView associated with a UIView
• GetLayoutHost() - retrieves the UILayoutHost hosting a UIView

(for these methods to work, the view must be in a layout hierarchy that is currently hosted by a UILayoutHost)

More Examples

Changing a view's margins:

_label.GetNativeView().LayoutMargins.Right = 100;
_label.GetLayoutHost().SetNeedsLayout();

Toggling a view between Visibility.Visible and Visibility.Gone:

_label.GetNativeView().Gone = !_label.GetNativeView().Gone;
_label.GetLayoutHost().SetNeedsLayout();

Inserting a new view into the view hierarchy:

_layout.AddSubView(new UILabel(RectangleF.Empty)) { ... };
_layout.GetLayoutHost().SetNeedsLayout();

Removing a view from the view hierarchy:

var host = _label.GetLayoutHost();				// We need to get the host before removing the view
_label.GetNativeView().RemoveFromSuperview();
host.SetNeedsLayout();

Adding a layer to a view group. Although this doesn't actually change the layout, the positioning of a ViewGroup's layer happens as part of the measure/layout cycle.

_viewGroup.Label = new CAGradientLayer() { ... };
_viewGroup.GetLayoutHost().SetNeedsLayout();