You should add a breakpoint in the line foto.Source = Zdjecie; to see if you have get the correct value of Zdjecie. I wrote a simple demo and it works on my sided, you can check below codes:
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
}
private void Button_Clicked(object sender, EventArgs e)
{
string jsonStr = "[{'Nazwa': 'Czekolada mleczna Sport & Fitness','Opis': 'Przykładowy opis produktu Czekolada mleczna Sport & Fitness', 'Zdjecie': 'https://interactive-examples.mdn.mozilla.net/media/examples/grapefruit-slice-332-332.jpg'}]";
var ObjContactList = JsonConvert.DeserializeObject<List<RootObject>>(jsonStr);
RootObject obj = ObjContactList[0];
foto.Source = obj.Zdjecie;
}
}
public class RootObject
{
public string Nazwa { get; set; }
public string Opis { get; set; }
public string Zdjecie { get; set; }
}
And in Xaml:
<StackLayout>
<!-- Place new controls here -->
<Button Clicked="Button_Clicked" Text="Click to load the Image"
HorizontalOptions="Center"
/>
<Image HorizontalOptions="Center" Source="" x:Name="foto"
WidthRequest="200" HeightRequest="200"/>
</StackLayout>