将 WPF 中的图像源绑定到 URL

我一直在浏览不同的帖子，试图找出我的问题出了什么问题。基本上我的用户控件上有一个 Image 标签，以及我想绑定到 url 的 Source。然而这不起作用。我尝试过使用返回的 ValueConverterBitmapImage(new Uri((string)value));但这不起作用。我唯一能得到的是你不能绑定到一个网址，你必须下载你想要绑定的图像。我不想下载我搜索的所有图像。是否有解决方法可以完成此任务，而无需在本地下载图像。我认为 ValueConverter 方法返回 BitmapImage 是最好的。请帮忙？

public class MyViewModel
{
    private string _posterUrl;
        public string PosterUrl
        {
            get
            {
                //Get Image Url, this is an example and will be retrieved from somewhere else.
                _posterUrl = "http://www.eurobuzz.org/wp-content/uploads/2012/08/logo.jpg";
                return _posterUrl;    
            }
            set 
            { 
                _posterUrl = value;
                NofityPropertyChanged(p => p.PosterUrl);
            }
        }
}

这是我的值转换器：

public class BitmapImageConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(value is string)
            return new BitmapImage(new Uri((string)value, UriKind.RelativeOrAbsolute));

        if(value is Uri)
            return new BitmapImage((Uri)value);

        throw new NotSupportedException();
    }

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

这是我的 XAML：

<Image Source="{Binding PosterUrl, Converter={StaticResource bitmapImageConverter}}" Width="100" Height="100" />

因此，它绑定到包含 imageurl 的 PosterUrl 属性，并将其转换为位图图像。有任何想法吗？

Try it

<Image Helpers:ImageAsyncHelper.SourceUri="{Binding Url, IsAsync=True}" x:Name="img" />

Where

using System;
using System.Windows;
using System.Windows.Data;
using System.Windows.Controls;

public class ImageAsyncHelper : DependencyObject {
    public static Uri GetSourceUri(DependencyObject obj){
        return (Uri)obj.GetValue(SourceUriProperty);
    }

    public static void SetSourceUri(DependencyObject obj, Uri value){
        obj.SetValue(SourceUriProperty, value);
    }

    public static readonly DependencyProperty SourceUriProperty =
        DependencyProperty.RegisterAttached("SourceUri",
            typeof(Uri),
            typeof(ImageAsyncHelper),
            new PropertyMetadata { PropertyChangedCallback = (obj, e) =>
                ((Image)obj).SetBinding(
                    Image.SourceProperty,
                    new Binding("VerifiedUri"){
                        Source = new ImageAsyncHelper{
                            _givenUri = (Uri)e.NewValue
                        },
                        IsAsync = true
                    }
                )
            }
        );

    private Uri _givenUri;
    public Uri VerifiedUri {
        get {
            try {
                System.Net.Dns.GetHostEntry(_givenUri.DnsSafeHost);
                return _givenUri;
            }
            catch (Exception) {
                return null;
            }
        }
    }
}

And

public Uri Url {
    get {
        return new Uri(SomeString, UriKind.Absolute);
    }
}