扩展 Chris Baxter 的解决方案,此转换器使用本地版本(如果存在),否则下载并保存文件。
using System;
using System.Globalization;
using System.IO;
using System.Windows.Data;
using System.Windows.Media.Imaging;
namespace MyNamespace
{
public sealed class UriToCachedImageConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var url = value as string;
if (url == null)
return null;
var webUri = new Uri(url, UriKind.Absolute);
var filename = Path.GetFileName(webUri.AbsolutePath);
var localFilePath = Path.Combine("C:\\MyImagesFolder\\", filename);
if (File.Exists(localFilePath))
{
return BitmapFrame.Create(new Uri(localFilePath, UriKind.Absolute));
}
var image = new BitmapImage();
image.BeginInit();
image.CacheOption = BitmapCacheOption.OnLoad;
image.UriSource = webUri;
image.EndInit();
SaveImage(image, localFilePath);
return image;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
public void SaveImage(BitmapImage image, string localFilePath)
{
image.DownloadCompleted += (sender, args) =>
{
var encoder = new PngBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create((BitmapImage) sender));
using (var filestream = new FileStream(localFilePath, FileMode.Create))
{
encoder.Save(filestream);
}
};
}
}
}
并确保您可以在您的 xaml 中访问转换器
<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:u="clr-namespace:MyNamespace"
d:DesignHeight="500"
d:DesignWidth="420">
<UserControl.Resources>
<ResourceDictionary>
<u:UriToCachedImageConverter x:Key="UrlToCachedImageConverter" />
</ResourceDictionary>
</UserControl.Resources>
</UserControl>
并在图像上使用转换器
<Image Source="{Binding URL, Mode=OneWay, Converter={StaticResource UrlToCachedImageConverter}, IsAsync=true}"/>