如何在xamarin.ios中添加放大和缩小按钮功能来更改地图比例？

// 创建放大按钮
UIButton zoomInButton = new UIButton(UIButtonType.Custom);
zoomInButton.Frame = new CGRect(10, 10, 50, 50);
zoomInButton.SetTitle("+", UIControlState.Normal);
zoomInButton.TouchUpInside += (sender, e) =>
{
    // 放大地图
    MKCoordinateSpan span = new MKCoordinateSpan(mapView.Region.Span.LatitudeDelta * 0.5, mapView.Region.Span.LongitudeDelta * 0.5);
    MKCoordinateRegion region = new MKCoordinateRegion(mapView.Region.Center, span);
    mapView.SetRegion(region, true);
};

// 创建缩小按钮
UIButton zoomOutButton = new UIButton(UIButtonType.Custom);
zoomOutButton.Frame = new CGRect(70, 10, 50, 50);
zoomOutButton.SetTitle("-", UIControlState.Normal);
zoomOutButton.TouchUpInside += (sender, e) =>
{
    // 缩小地图
    MKCoordinateSpan span = new MKCoordinateSpan(mapView.Region.Span.LatitudeDelta * 2, mapView.Region.Span.LongitudeDelta * 2);
    MKCoordinateRegion region = new MKCoordinateRegion(mapView.Region.Center, span);
    mapView.SetRegion(region, true);
};

// 将按钮添加到视图中
View.AddSubview(zoomInButton);
View.AddSubview(zoomOutButton);