在我们实际工程中，很多情况需要从网络上加载图片，然后将图片在imageview中显示出来，但每次都要从网络上请求，会严重影响用户体验，为了不是每次显示都需要从网上下载数据，希望将图片放到本地缓存，因此我们需要一个好的的缓存策略，今天我将我在项目工程中的实际经验分享给大家，我这里主要介绍一下强大的ASIHTTPRequest的缓存策略，以及使用方法：

 

    下面是具体步骤：

一、设置缓存策略

    首先在SplitDemoAppDelegate委托代理中，实现如下代码：

    在SplitDemoAppDelegate.h文件中，代码如下：

 

1 #import 
     
        2  3 @class ASIDownloadCache;  4  5 @interface SplitDemoAppDelegate : NSObject 
      
        {
     6  7     UIWindow *_window;  8  9     ASIDownloadCache*_downloadCache;            //下载缓存策略 10 11 } 12 13 @property (nonatomic, retain) ASIDownloadCache*downloadCache; 14 15 @end
      
     

 

在SplitDemoAppDelegate.m文件中，代码如下:

1 #import "SplitDemoAppDelegate.h"  2  3 @implementation SplitDemoAppDelegate  4  5 @synthesize window=_window;  6  7 @synthesize downloadCache = _downloadCache;  8  9 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions 10 11 {
     12 13     //初始化ASIDownloadCache缓存对象 14 15    ASIDownloadCache *cache = [[ASIDownloadCache alloc] init]; 16 17    self.downloadCache = cache; 18 19   [cache release]; 20 21 22    //路径 23 24    NSArray *paths =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES); 25 26   NSString *documentDirectory = [paths objectAtIndex:0]; 27 28    //设置缓存存放路径 29 30    [self.downloadCache setStoragePath:[documentDirectorystringByAppendingPathComponent:@"resource"]]; 31 32    //设置缓存策略 33 34     [self.downloadCache setDefaultCachePolicy:ASIOnlyLoadIfNotCachedCachePolicy]; 35 36     // Override point for customization after application launch. 37 38     [self.window makeKeyAndVisible]; 39 40     return YES; 41 42 } 43 44 45 - (void)dealloc 46 47 {
     48 49     [_window release]; 50 51     [_downloadCache release]; 52 53    [super dealloc]; 54 55 } 56 57 @end

 

    二、创建缓存线程

    这一步是创建一个NSOperation类，实现缓存的方法，代码如下：

    ResourceContainer.h文件实现：

 

1 #import 
          
             2  3 #import "ASIHTTPRequest.h"  4  5 #import "SplitDemoAppDelegate.h"  6  7   8  9 @interface ResourceContainer : NSOperation {
         10 11 NSURL*_resourceURL;            //资源请求url 12 13 NSObject*_hostObject;             14 15 SEL_resourceDidReceive;      //资源接手响应方法  16 17 SplitDemoAppDelegate*_appDelegate;            //应用委托对象 18 19 ASIHTTPRequest*_httpRequest;            20 21 UIImageView*_imageView;              22 23 } 24 25  26 27 @property (nonatomic, retain) NSURL*resourceURL; 28 29 @property (nonatomic, retain) NSObject*hostObject; 30 31 @property (nonatomic, assign) SELresourceDidReceive; 32 33 @property (nonatomic, assign) SplitDemoAppDelegate   *appDelegate; 34 35 @property (nonatomic, retain) ASIHTTPRequest*httpRequest; 36 37 @property (nonatomic, retain) UIImageView*imageView; 38 39  40 41 //http请求回调方法 42 43 -(void)didStartHttpRequest:(ASIHTTPRequest *)request; 44 45 -(void)didFinishHttpRequest:(ASIHTTPRequest *)request; 46 47 -(void)didFailedHttpRequest:(ASIHTTPRequest *)request; 48 49  50 51 //取消资源请求 52 53 -(void)cancelReourceGet; 54 55 //资源接收回调方法 56 57 -(void)resourceDidReceive:(NSData *)resource; 58 59 @end
          

 

ResourceContainer.m文件实现：

1 #import "ResourceContainer.h"   2 #import "HttpConstant.h"   3 #import "ASIDownloadCache.h"   4 @implementation ResourceContainer   5 @synthesize resourceURL = _resourceURL;   6 @synthesize hostObject = _hostObject;   7 @synthesize resourceDidReceive = _resourceDidReceive;   8 @synthesize appDelegate = _appDelegate;   9 @synthesize httpRequest = _httpRequest;  10 @synthesize imageView = _imageView;  11  12 -(id)init{
         13  14      if(self == [super init]){
         15  16      self.appDelegate = (SplitDemoAppDelegate *)[[UIApplication        sharedApplication] delegate];  17  18       }  19  20    return self;  21  22 }  23  24  25 -(void)main{
         26  27       if(self.hostObject == nil)  28       return;  29  30      if(self.resourceURL == nil){
         31           [self resourceDidReceive:nil];  32           return;  33      }  34  35       ASIHTTPRequest *request = [ASIHTTPRequest     requestWithURL:self.resourceURL]  36       self.httpRequest = request;  37  38   39  40 [self.httpRequest setDownloadCache:self.appDelegate.downloadCache];  41 [self.httpRequest setDelegate:self];  42 [self.httpRequest setDidStartSelector:@selector(didStartHttpRequest:)];  43 [self.httpRequest setDidFinishSelector:@selector(didFinishHttpRequest:)];  44 [self.httpRequest setDidFailSelector:@selector(didFailedHttpRequest:)];  45  46     //发异步请求  47  48 [self.httpRequest startAsynchronous];  49  50 }  51  52 - (void)dealloc {
         53  54 [_resourceURL release];  55 [_hostObject release];  56 [_httpRequest release];  57 [_imageView release];  58 [super dealloc];  59  60 }  61  62 //开始请求  63  64 -(void)didStartHttpRequest:(ASIHTTPRequest *)request{
         65  66 [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];  67  68 }  69  70 //请求成功返回处理结果  71  72 -(void)didFinishHttpRequest:(ASIHTTPRequest *)request{
         73  74 [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];  75  76   77  78     if([request responseStatusCode] == 200 || [request responseStatusCode] == 304){
         79  80 //判断是否来自缓存  81  82         if([request didUseCachedResponse]){
         83  84 NSLog(@"=========资源请求：%@ 来自缓存============",[self.resourceURL absoluteURL]);  85  86         }  87          else{
         88  89             NSLog(@"=========资源请求：图片不来自缓存============");  90         }  91  92  93      [self resourceDidReceive:[request responseData]];  94  95 }  96  97 else {
         98  99        [self resourceDidReceive:nil]; 100 101        } 102 103 } 104 105 //失败请求返回处理结果 106 107 -(void)didFailedHttpRequest:(ASIHTTPRequest *)request{
        108 109 [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO]; 110 111 [self resourceDidReceive:nil]; 112 113 } 114 115 //取消资源请求 116 117 -(void)cancelReourceGet{
        118 119 [self.httpRequest cancel]; 120 121 } 122 123 //资源接收处理方法 124 125 -(void)resourceDidReceive:(NSData *)resource{
        126 127 if([self.hostObject respondsToSelector:self.resourceDidReceive]){
        128 129 if(resource != nil && self.imageView != nil){
        130 131 self.imageView.image = [UIImage imageWithData:resource]; 132 133 } 134 135 136 [self.hostObject performSelectorOnMainThread:self.resourceDidReceive withObject:self.imageViewwaitUntilDone:NO]; 137 138 } 139 140 } 141 142 @end

 

    到第二步，我们的缓存策略的设置，以及资源请求和接收数据方法已经构建完毕，下面介绍一下如何使用我们上面创建的NSOperation类

 

    三、图片请求（利用上面创建的类）

    这里以我的工程为例进行分析：

在DetailViewController.h声明文件中:

 

1 #import 
          
             2  3 @interface DetailViewController :UIViewController {
         4  5     NSURL                         *_imageURL;                    //图片url  6  7     NSMutableArray            *_originalIndexArray;        //保存请求图片的号  8  9     NSMutableDictionary     *_originalOperationDic;     //保存图片请求队列 10 11     NSOperationQueue        *_requestImageQueue;    //图片请求队列 12 13 } 14 15 @property (nonatomic, retain) NSURL                       *imageURL; 16 @property (nonatomic, retain) NSMutableArray          *originalIndexArray; 17 @property (nonatomic, retain) NSMutableDictionary   *originalOperationDic; 18 @property (nonatomic, retain) NSOperationQueue      * requestImageQueue; 19 20 //显示图片信息 21 22 -(void)displayProductImage; 23 24 //根据图片序号显示请求图片资源 25 26 -(void)displayImageByIndex:(NSInteger)index ByImageURL:(NSURL *)url; 27 28 //处理图片请求返回信息 29 30 -(void)imageDidReceive:(UIImageView *)imageView; 31 32 @end
          

 

 在DetailViewController.m实现文件中:

1 #import "ProductDetailViewController.h"   2   3 //这里引入在第二步中，我们创建的对象   4 #import "ResourceContainer.h"   5   6 @implementation DetailViewController   7 @synthesize imageURL = _imageURL;   8 @synthesize originalIndexArray = _originalIndexArray;   9 @synthesize originalOperationDic = _originalOperationDic;  10 @synthesize requestImageQueue = _requestImageQueue;  11  12  13 - (void)viewDidLoad  14  15 {
         16  17      [super viewDidLoad];  18      NSOperationQueue *tempQueue = [[NSOperationQueue alloc] init];  19  20      self.requsetImageQueue = tempQueue;  21      [tempQueue release];  22  23       NSMutableArray *array = [[NSMutableArray alloc] init];  24  25       self.originalIndexArray = array;  26       [array release];  27  28        NSMutableDictionary *dic = [[NSMutableDictionary alloc] init];  29  30        self.originalOperationDic = dic;  31        [dic release];  32  33 }  34  35 //显示图片信息  36  37 -(void)displayProductImage  38  39 {
         40  41     NSURL *url = [NSURL URLWithString:@"http://xxx.xxx.xxx.xxx"];  42  43     //这个是从器返回有图片数目，self.xxxx根据具体的场合  44  45     int imageCount = [self.xxxx.imageNum intValue];  46  47     for (int i=0; i

    经过上述步骤，我们实现了加载网络图片时缓存功能，增强了用户体验效果。代码中可能会有诸多问题，希望网友指教，有更好的缓存方法，也希望一起交流！