Sets up a source for the icon that is shown in the header of the column sorted in ascending order.
The Xamarin.Forms.ImageSource object, that specifies the image source.
GridControl provides you with two predefined themes - Light and Dark. The Default theme depends on the mobile platform. For iOS applications, the Default theme is Light, for Android - is Dark. To apply another theme to a grid, use the ThemeManager.ThemeName property. Then, you can customize the applied theme (if needed). For more information, see the How to: Customize Themes document.
To apply customization to a grid, call the ThemeManager.RefreshTheme method.
The CreateArrowUpImageSource method is abstract. So, to change the image source shown in your grid, override the method in the IHeaderCustomizer descendants.