How load binary images in Xamarin

问题:

I'm working with Xamarin Forms and I want to load a listview with imagecells, also I'm binding the data with XAML. My webservice provider returns me the binary code of the images, ¿someone knows how I can convert this to show the image?

This is my XAML listview template:

    <ListView x:Name="lv_products">

      <ListView.ItemTemplate>
        <DataTemplate>
          <ImageCell
                    Text="{Binding Name}"
                    Detail="{Binding Description}"
                    ImageSource="{Binding Image, Converter={StaticResource cnvImage}}">
          </ImageCell>
        </DataTemplate>

      </ListView.ItemTemplate>
    </ListView>

And the converter:

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value != null && value is byte[])
        {

            byte[] binary = (byte[])value;

            Image image = new Image();
            image.Source = ImageSource.FromStream(() => new MemoryStream(binary));

            return image.Source;
        }
        return null;
    }

But picture appears empty (transparent).

回答1:

Here is working converter. I use MemoryStream and ImageSource.FromStream.

public class ByteImageConverter : IValueConverter
{
    public object Convert(object value, Type targetType,
                          object parameter, CultureInfo culture)
    {
        var image = value as byte[];
        if (image == null)
            return null;
        return ImageSource.FromStream(() => new MemoryStream(image));
    }

    public object ConvertBack(object value, Type targetType,
                              object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Just as sample here is my page

public partial class Page : ContentPage
{
    readonly ViewModel _bindingContext = new ViewModel();

    public Page()
    {
        InitializeComponent();

        BindingContext = _bindingContext;
        LoadImage();
    }

    private async void LoadImage()
    {
        var assembly = typeof (ByteImageConverter).GetTypeInfo().Assembly;
        var stream = assembly
              .GetManifestResourceStream("TestImage.c5qdlJqrb04.jpg");
        using (var ms = new MemoryStream())
        {
            await stream.CopyToAsync(ms);
            _bindingContext.Image = ms.ToArray();
        }
    }
}

public class ViewModel : INotifyPropertyChanged
{
    private byte[] _image;
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(
                             [CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }

    public byte[] Image
    {
        get { return _image; }
        set
        {
            _image = value;
            OnPropertyChanged();
        }
    }
}

回答2:

If you have a URL which returns the image file, why aren't you just use the URL as ImageSource ?

  <ImageCell  Text="{Binding Name}"
              Detail="{Binding Description}"
              ImageSource="{Binding ImageURL}">
  </ImageCell>

回答3:

You can convert byte array to Bitmap image, and assign that bitmap to the ImageView. I did this in Xamarin.Android, dnt know will it work with forms or not.

bitmap = BitmapFactory.DecodeByteArray(byte, 0, byte.Length);

Then use imageView.FromBitmap() to display this image.