绑定来自SQLite数据库，Xamarin表单的ListView图像

Question

I have a Person model:

 public class Person
 {
    [PrimaryKey, AutoIncrement]
    public int Id { get; set; }
    public string FirstName{ get; set; }
    public string LastName{ get; set; }
    public byte[] Image { get; set; }
 }

In my SQLite database I have pictures stored in the table. I'm trying to show the images in a ListView. So implemented a ImageConverter:

  public class ImageConverter : IValueConverter
{
  public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        ImageSource retSource = null;
        if (value != null)
        {
            byte[] imageAsBytes = (byte[])value;
            var stream = new MemoryStream(imageAsBytes);
            retSource = ImageSource.FromStream(() => stream);
        }
        return retSource;
    }
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo     culture)
    {
        throw new NotImplementedException();
    }

}

In the Xaml code I'm trying to bind och convert the image like this:

<Page.Resources>
    <converters:ImageConverter x:Key="ImageConverter" />
</Page.Resources>
<ContentPage.Content>
    <ListView x:Name="PersonListView">

        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell Height="220">
                  <Image Source="{Binding Image, Converter={StaticResource ImageConverter}}"/>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</ContentPage.Content>

When I run the page I get this error:

System.NullReferenceException: Object reference not set to an instance of an object.

I don't understand where it's wrong in my code. How can I view pictures from my database?

Answer 1

Try this code in your converter and let me know it works or not:

public class ImageConverter : IValueConverter
{
  public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {                        
        return "data:image;base64," + Convert.ToBase64String(value);;
    }
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo     culture)
    {
        throw new NotImplementedException();
    }

}