How to zoom the whole gantt when the FontSize changes?

To zoom the gantt's UI when the FontSize changes for example, do this:

// In your MainPage.xaml.cs, for example

double oldSize = this.FontSize;

// Change the font size.

this.FontSize = 11;

// Adjust the zoom level to reflect the font size change.

this.gantt.ZoomUIByFactor(this.FontSize / oldSize);