WP7应用开发笔记 继承BitmapSource并使用独立存储来缓存远程的图片

作为Web App访问远程图片是经常的遇到功能，Wp本身提供了Image 很好的支持通过图片的Uri显示图片

public ImageSource Source { get; set; }

<Image Source="https://www.google.com/intl/en_com/images/srpr/logo3w.png" />

为了减少网络流量，需要将图片缓存到本地数据存储中。复习一下WP的本地数据存储：

 

Windows Phone 本地数据存储

Windows Phone 应用程序可以使用独立存储将数据储存到手机本地。应用程序可以通过三种方式储存数据：

1. 设置：使用 IsolatedStorageSettings 类将数据存储为键/值对。
2. 文件和文件夹：使用 IsolatedStorageFile 类存储文件和文件夹。
3. 本地数据库：7.1新增，只能支持LINQ TO SQL ，不能写SQL语句。

本地存储图片

首先图片应该选择IsolatedStorageFile来存储：

WP提供了一个叫IsolatedStorageFileStream的Stream和FileStream操作一样

using (var fileStream = isolatedStorageFile.OpenFile(filePath, FileMode.OpenOrCreate, FileAccess.Write)) 
{ 
       stream.CopyTo(fileStream); 
}

缓存的思路

现在是思路是首先检查是否被缓存里，首先定义一个公用的缓存文件夹，在静态构造函数中创建文件夹

private const string CacheDirectory = "CachedImages"; 
        
        static StorageCachedImage() 
        {

            //创建缓存目录 
            using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()) 
            { 
                if (!isolatedStorageFile.DirectoryExists(CacheDirectory)) 
                { 
                    isolatedStorageFile.CreateDirectory(CacheDirectory); 
                } 
            } 
        }

然后将Url转换成文件名，我的方法比较简单直接替换’/’符号。使用FileExists判断文件是否存在

//文件路径 
filePath = Path.Combine(CacheDirectory, uriSource.AbsolutePath.TrimStart('/').Replace('/', '_'));

/// <summary> 
       /// 打开缓存源 
       /// </summary> 
       private void OpenCatchSource() 
       { 
           bool exist; 
           using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()) 
           { 
               exist = isolatedStorageFile.FileExists(filePath); 
           } 
           if (exist) 
           { 
               SetCacheStreamSource(); 
           } 
           else 
           { 
               SetWebStreamSource(); 
           } 
       } 

如果没有缓存则通过Uri下载图片并保存到IsolatedStorageFile。

使用httpWebRequest实现下载，使用IsolatedStorageFileStream保存图片

/// <summary> 
       /// 下载Uri中的图片 
       /// </summary> 
       private void SetWebStreamSource() 
       { 
           var httpWebRequest = (HttpWebRequest)WebRequest.Create(uriSource); 
           httpWebRequest.AllowReadStreamBuffering = true; 
           httpWebRequest.BeginGetResponse(ResponseCallBack, httpWebRequest); 
       }


       /// <summary> 
       /// 下载回调 
       /// </summary> 
       /// <param name="asyncResult"></param> 
       private void ResponseCallBack(IAsyncResult asyncResult) 
       { 
           var httpWebRequest = asyncResult.AsyncState as HttpWebRequest; 
           if(httpWebRequest == null)return; 
           try 
           { 
               var response = httpWebRequest.EndGetResponse(asyncResult); 
               using(var stream = response.GetResponseStream()) 
               using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()) 
               using (var fileStream = isolatedStorageFile.OpenFile 
                   (filePath, FileMode.OpenOrCreate, FileAccess.Write)) 
               { 
                   stream.CopyTo(fileStream);//保存到本地 
               } 
               Dispatcher.BeginInvoke(SetCacheStreamSource); 
           } 
           catch(Exception err) 
           { 
               Debug.WriteLine(err.Message); 
           } 
       } 

保存到本地后下载，用IsolatedStorageFileStream打开本地图像流，并通过父类的SetSource设置图片流。

private void SetCacheStreamSource() 
       { 
           using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication()) 
           using (var stream = isolatedStorageFile.OpenFile(filePath, FileMode.Open, FileAccess.Read)) 
           { 
               SetSource(stream); 
           } 

完整代码如下：

using System;
using System.Diagnostics;
using System.IO;
using System.IO.IsolatedStorage;
using System.Net;
using System.Windows.Media.Imaging;

namespace KimiStudio.Controls
{
    /// <summary>
    /// 独立存储缓存的图片源
    /// </summary>
    public sealed class StorageCachedImage : BitmapSource
    {
        private readonly Uri uriSource;
        private readonly string filePath;
        private const string CacheDirectory = "CachedImages";
        
        static StorageCachedImage()
        {

            //创建缓存目录
            using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
            {
                if (!isolatedStorageFile.DirectoryExists(CacheDirectory))
                {
                    isolatedStorageFile.CreateDirectory(CacheDirectory);
                }
            }
        }

        /// <summary>
        /// 创建一个独立存储缓存的图片源
        /// </summary>
        /// <param name="uriSource"></param>
        public StorageCachedImage(Uri uriSource)
        {
            this.uriSource = uriSource;

            //文件路径
            filePath = Path.Combine(CacheDirectory, uriSource.AbsolutePath.TrimStart('/').Replace('/', '_'));
            OpenCatchSource();
        }

        /// <summary>
        /// 打开缓存源
        /// </summary>
        private void OpenCatchSource()
        {
            bool exist;
            using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
            {
                exist = isolatedStorageFile.FileExists(filePath);
            }
            if (exist)
            {
                SetCacheStreamSource();
            }
            else
            {
                SetWebStreamSource();
            }
        }

        /// <summary>
        /// 设置缓存流到图片
        /// </summary>
        private void SetCacheStreamSource()
        {
            using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
            using (var stream = isolatedStorageFile.OpenFile(filePath, FileMode.Open, FileAccess.Read))
            {
                SetSource(stream);
            }
        }

        /// <summary>
        /// 下载Uri中的图片
        /// </summary>
        private void SetWebStreamSource()
        {
            var httpWebRequest = (HttpWebRequest)WebRequest.Create(uriSource);
            httpWebRequest.AllowReadStreamBuffering = true;
            httpWebRequest.BeginGetResponse(ResponseCallBack, httpWebRequest);
        }


        /// <summary>
        /// 下载回调
        /// </summary>
        /// <param name="asyncResult"></param>
        private void ResponseCallBack(IAsyncResult asyncResult)
        {
            var httpWebRequest = asyncResult.AsyncState as HttpWebRequest;
            if(httpWebRequest == null)return;
            try
            {
                var response = httpWebRequest.EndGetResponse(asyncResult);
                using(var stream = response.GetResponseStream())
                using (var isolatedStorageFile = IsolatedStorageFile.GetUserStoreForApplication())
                using (var fileStream = isolatedStorageFile.OpenFile
                    (filePath, FileMode.OpenOrCreate, FileAccess.Write))
                {
                    stream.CopyTo(fileStream);
                }
                Dispatcher.BeginInvoke(SetCacheStreamSource);
            }
            catch(Exception err)
            {
                Debug.WriteLine(err.Message);
            }
        }
    }

   
}

测试

定义一个Image

Uri uriSource = new Uri(@”https://www.google.com/intl/en_com/images/srpr/logo3w.png”);

image1.ImageSource = new StorageCachedImage(uriSource);

用IsoStoreSpy查看（这里是我APP实际的图)