您可以使用自定义渲染器:

You could do it with custom renderer:

[assembly:ExportRenderer (typeof(NavigationPage), typeof(NavigationPageRenderer))]
namespace SuperForms.Samples.Droid
{
    public class NavigationPageRenderer : NavigationRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<NavigationPage> e)
        {
            base.OnElementChanged(e);

            var actionBar = ((Activity)Context).ActionBar;
            actionBar.SetIcon(Resource.Drawable.newIcon);
        }
    }
}

将图标添加到Resources/drawable文件夹:

外观如何: