Change image transparency with binding?

The Xamarin application has the following page structure: (to the center by content) Frame - StackLayout - ScrollView -Grid with two rows and one column - both an Image element in the first line and lable in the second label. Here is the actual code:

InitializeComponent(); Label lb = new Label { Text="pasta"}; img = new Image {Source ="pasta.jpg" }; Frame fr = new Frame { HeightRequest=250, WidthRequest=250 }; StackLayout st = new StackLayout {HeightRequest=fr.HeightRequest , WidthRequest =fr.WidthRequest , Orientation=StackOrientation.Vertical }; sc = new ScrollView { WidthRequest=st.WidthRequest , HeightRequest = st.HeightRequest }; Grid gr = new Grid { RowDefinitions = { new RowDefinition { Height =new GridLength(sc.HeightRequest) }, new RowDefinition { Height = new GridLength(sc.HeightRequest) } } , ColumnDefinitions = { new ColumnDefinition { Width = new GridLength(sc.WidthRequest)} } }; gr.Children.Add(img,0,0); gr.Children.Add(lb, 0, 1); sc.Content = gr; sc.Scrolled += On_scroll; st.Children.Add(sc); fr.Content = st; this.Content = fr; 

Now, what is actually required: it is necessary that the transparency of the image would decrease when scrolling. For this, I am Scrolled to the Scrolled event Scrolled

  sc.Scrolled += On_scroll; stp = new Stepper { Increment=0.5}; img.BindingContext = Img_Pr;//привязываем Img_Pr к img.BindingContext private void On_scroll(object sender, ScrolledEventArgs e) { stp.ValueChanged += Scroll_Step_img; //вызываем обработку stepper } 

to control the degree of transparency - I use Stepper - the handler of which I call in the event handler for the Scrolled event. On the Stepper object - stp - I call the ValueChanged event and subscribe a handler to it.

In order to control the transparency of the image - it does not have such a property, I decided to create a BindableProperty

 public class Image_Property_Class : Xamarin.Forms.Image { public static readonly BindableProperty transperentProperty = BindableProperty.Create("Transparent", typeof(Color), typeof(Xamarin.Forms.Image), new Color(255, 255, 255, 0)); public Color Transparent { set { SetValue(transperentProperty,value); } get { return (Color)GetValue(transperentProperty); } } } 

-For this, I created a class that is examined from the Image class and already in it created BindableProperty. In theory, through it, I want to change the value of the alpha channel of the original image - making it more transparent.

 public static Image_Property_Class Img_Pr = new Image_Property_Class { };//объект привязки 

In the event handler of the ValueChanged event of the ValueChanged object

 public static void Scroll_Step_img(object sender, ValueChangedEventArgs e) { //настраиваем объект привязки Img_Pr.SetBinding(Image_Property_Class.transperentProperty, "img.BackgroundColor"); //устанавливаем новое значение Img_Pr.Transparent = new Color(img.BackgroundColor.R, img.BackgroundColor.G, img.BackgroundColor.B, e.NewValue); } 

I set up a binding by setting the dependency and passing the Transperent property itself — a new value in the form of the -e event argument. But at the same time when scrolling the image does not become more transparent. Here is the complete code in order:

  ScrollView sc; public static Image img; Stepper stp; public MainPage() { InitializeComponent(); Label lb = new Label { Text="pasta"}; img = new Image {Source ="pasta.jpg" }; Frame fr = new Frame { HeightRequest=250, WidthRequest=250 }; StackLayout st = new StackLayout {HeightRequest=fr.HeightRequest , WidthRequest =fr.WidthRequest , Orientation=StackOrientation.Vertical }; sc = new ScrollView { WidthRequest=st.WidthRequest , HeightRequest = st.HeightRequest }; Grid gr = new Grid { RowDefinitions = { new RowDefinition { Height =new GridLength(sc.HeightRequest) }, new RowDefinition { Height = new GridLength(sc.HeightRequest) } } , ColumnDefinitions = { new ColumnDefinition { Width = new GridLength(sc.WidthRequest)} } }; gr.Children.Add(img,0,0); gr.Children.Add(lb, 0, 1); sc.Content = gr; sc.Scrolled += On_scroll; st.Children.Add(sc); fr.Content = st; this.Content = fr; stp = new Stepper { Increment=0.5}; img.BindingContext = Img_Pr;//привязываем Img_Pr к img.BindingContext } public static Image_Property_Class Img_Pr = new Image_Property_Class { };//объект привязки private void On_scroll(object sender, ScrolledEventArgs e) { stp.ValueChanged += Scroll_Step_img; //вызываем обработку stepper } public static void Scroll_Step_img(object sender, ValueChangedEventArgs e) { //настраиваем объект привязки Img_Pr.SetBinding(Image_Property_Class.transperentProperty, "img.BackgroundColor"); //устанавливаем новое значение Img_Pr.Transparent = new Color(img.BackgroundColor.R, img.BackgroundColor.G, img.BackgroundColor.B, e.NewValue); } } 

BindablePeoperty

 public class Image_Property_Class : Xamarin.Forms.Image { public static readonly BindableProperty transperentProperty = BindableProperty.Create("Transparent", typeof(Color), typeof(Xamarin.Forms.Image), new Color(255, 255, 255, 0)); public Color Transparent { set { SetValue(transperentProperty,value); } get { return (Color)GetValue(transperentProperty); } } }