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="http://up.2cto.com/2012/0301/20120301094720431.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(@”http://up.2cto.com/2012/0301/20120301094720431.png”);
image1.ImageSource = new StorageCachedImage(uriSource);
用IsoStoreSpy查看（这里是我APP实际的图)
摘自 Kiminozo's Tech Blog