windows phone 图片缓存-优快云博客

本文介绍了一种自定义的缓存机制，用于高效地加载图像资源，并通过实例展示了如何在WPF应用程序中应用该机制。通过实现一个缓存类和相应的属性绑定，实现了图像的本地缓存与远程加载的结合，提高了用户体验和资源利用率。

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media.Imaging;
using System.Text;
using System.IO.IsolatedStorage;
using System.IO;

namespace Cache
{
    public class ImageCache : DependencyObject
    {
        public static readonly DependencyProperty SourceProperty = DependencyProperty.RegisterAttached(
          "Source",
          typeof(String),
          typeof(ImageCache),
          new PropertyMetadata(String.Empty, OnSourceChanged)
          );
        public static void SetSource(DependencyObject source, String value)
        {
            source.SetValue(SourceProperty, value);
        }
        public static String GetSource(DependencyObject source)
        {
            return (String)source.GetValue(SourceProperty);
        }

        private static void OnSourceChanged(DependencyObject target, DependencyPropertyChangedEventArgs args)
        {
            String value = args.NewValue as String;
            if (String.IsNullOrEmpty(value) == true)
            {
                return;
            }
            Image image = target as Image;
            if (image != null)
            {
                image.Source = new BitmapWithCacheSource(value);
                return;
            }
            BitmapImage bitmapImage = target as BitmapImage;
            if (bitmapImage != null)
            {
                new BitmapWithCacheSource(value, bitmapImage);
                return;
            }
        }
    }
    public sealed class BitmapWithCacheSource : BitmapSource
    {
        private static readonly Encoding UTF8Encoding = Encoding.UTF8;
        public const string IMAGECACHEDIRECTORY = "ImagesCache/";
        private IsolatedStorageFile _iso = IsolatedStorageFile.GetUserStoreForApplication();

        private readonly String _imageWebUrl;
        private readonly String _imageCacheFileName;

        static BitmapWithCacheSource()
        {
            String imageCacheDriectory = IMAGECACHEDIRECTORY.TrimEnd('/');
            IsolatedStorageFile iso = IsolatedStorageFile.GetUserStoreForApplication();
            if (iso.DirectoryExists(imageCacheDriectory) == false)
            {
                iso.CreateDirectory(imageCacheDriectory);
            }
        }

        private String ToInternalKey(String value)
        {
            if (String.IsNullOrEmpty(value))
            {
                return String.Empty;
            }
            String exName = value.Substring(value.LastIndexOf('.'));
            byte[] bytes = UTF8Encoding.GetBytes(value);
            return Convert.ToBase64String(bytes) + exName;
        }

        public BitmapWithCacheSource(String imageWebUrl) : this(imageWebUrl, null) { }

        public BitmapWithCacheSource(String imageWebUrl, BitmapImage bitmapImage)
        {
            this._imageWebUrl = imageWebUrl;
            this._imageCacheFileName = IMAGECACHEDIRECTORY + ToInternalKey(this._imageWebUrl);
            this.SetImageStreamSource(bitmapImage);
        }

        private void SetImageStreamSource(BitmapImage bitmapImage)
        {
            BitmapSource bitmapSource = this;
            if (bitmapImage != null)
            {
                bitmapSource = bitmapImage;
            }
            if (_iso.FileExists(this._imageCacheFileName) == true)
            {
                SetImageCacheStreamSource(bitmapSource);
                return;
            }
            if (bitmapImage == null)
            {
                SetImageWebStreamSource();
                return;
            }
            bitmapImage.UriSource = new Uri(this._imageWebUrl, UriKind.Absolute);
            bitmapImage.ImageOpened += bitmapImage_ImageOpened;
        }

        private void bitmapImage_ImageOpened(object sender, RoutedEventArgs e)
        {
            BitmapImage bitmapImage = (BitmapImage)sender;
            bitmapImage.ImageOpened -= bitmapImage_ImageOpened;
            WriteableBitmap writeableBitmap = new WriteableBitmap(bitmapImage);
            using (var fileStream = this._iso.OpenFile(this._imageCacheFileName, FileMode.Create, FileAccess.Write))
            {
                writeableBitmap.SaveJpeg(fileStream, bitmapImage.PixelWidth, bitmapImage.PixelHeight, 0, 100);
            }
        }

        private void SetImageCacheStreamSource(BitmapSource source)
        {
            using (var imageStream = this._iso.OpenFile(this._imageCacheFileName, FileMode.Open, FileAccess.Read))
            {
                source.SetSource(imageStream);
            }
        }

        private void SetImageWebStreamSource()
        {
            var httpWebRequest = (HttpWebRequest)WebRequest.Create(this._imageWebUrl);
            httpWebRequest.AllowReadStreamBuffering = true;
            httpWebRequest.BeginGetResponse(ResponseCallBack, httpWebRequest);
        }

        private void ResponseCallBack(IAsyncResult asyncResult)
        {
            var httpWebRequest = asyncResult.AsyncState as HttpWebRequest;
            try
            {
                var response = httpWebRequest.EndGetResponse(asyncResult);
                var stream = response.GetResponseStream();
                using (var fileStream = this._iso.OpenFile(this._imageCacheFileName, FileMode.Create, FileAccess.Write))
                {
                    stream.CopyTo(fileStream);
                    base.Dispatcher.BeginInvoke(() =>
                    {
                        stream.Seek(0, SeekOrigin.Begin);
                        base.SetSource(stream);
                        stream.Dispose();
                    });
                }
            }
            catch
            {

            }
        }

    }
}

　　调用方法

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
        {
            base.OnNavigatedTo(e);
            this.imagesStackPanel.DataContext = "url";
        }

private void Button_Click(object sender, RoutedEventArgs e)
        {
            BitmapImage bitmapImage = new BitmapImage();
            bitmapImage.DownloadProgress += bitmapImage_DownloadProgress;
            //使用方式2
            Cache.ImageCache.SetSource(bitmapImage,"url");
            this.bitmapImageImage.Source = bitmapImage;
        }

        void bitmapImage_DownloadProgress(object sender, DownloadProgressEventArgs e)
        {
            this.imageDownloadProgress.Value = e.Progress;
        }

　　前台：

<StackPanel x:Name="imagesStackPanel"
                xmlns:cache="clr-namespace:Cache"
                Margin="20">
        <!--使用方式1-->
        <Image cache:ImageCache.Source="{Binding}"
               MaxHeight="300" />

        <Button Content="使用BitmapImage"
                Click="Button_Click" />
        <ProgressBar x:Name="imageDownloadProgress"
                     VerticalAlignment="Top" />
        <Image x:Name="bitmapImageImage"
               MaxHeight="300" />
    </StackPanel>