xamarin forms custom layout

All layouts are derived from Xamarin.Forms.Layout. (i.e. StackLayout, Grid, RelativeLayout etc..)
Layout class is reponsible for adding and removing children from layout.

Layout must to override 'LayoutChildren' method and 'LayoutChildren' method is responsible for postioning children on screen.
Here you can set postion of each child on screen.

Another 'OnSizeRequest' method is required to make sure layout is sized correctly when it is placed inside other layout.