IOS开发网络加载图片缓存策略之──ASIDownloadCache缓存策略

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：

#import <UIKit/UIKit.h>
@class ASIDownloadCache;

@interface SplitDemoAppDelegate : NSObject <UIApplicationDelegate,UITabBarControllerDelegate> {
    UIWindow *_window;
    ASIDownloadCache *_downloadCache;            //下载缓存策略
}
 
@property (nonatomic, retain) ASIDownloadCache *downloadCache;
@end

    在SplitDemoAppDelegate.m文件中，代码如下：

#import "SplitDemoAppDelegate.h"
@implementation SplitDemoAppDelegate
@synthesize window=_window;
@synthesize downloadCache = _downloadCache;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions
{
    //初始化ASIDownloadCache缓存对象
   ASIDownloadCache *cache = [[ASIDownloadCache alloc] init];
   self.downloadCache = cache;
  [cache release];
 
   //路径
   NSArray *paths =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
  NSString *documentDirectory = [paths objectAtIndex:0];
   //设置缓存存放路径
   [self.downloadCache setStoragePath:[documentDirectorystringByAppendingPathComponent:@"resource"]];
   //设置缓存策略
    [self.downloadCache setDefaultCachePolicy:ASIOnlyLoadIfNotCachedCachePolicy];
    // Override point for customization after application launch.
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)dealloc
{
    [_window release];
    [_downloadCache release];
   [super dealloc];
}
 
@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：

#import <Foundation/Foundation.h>
#import "ASIHTTPRequest.h"
#import "SplitDemoAppDelegate.h"
 
@interface ResourceContainer : NSOperation {
NSURL *_resourceURL;            //资源请求url
NSObject *_hostObject;             
SEL _resourceDidReceive;      //资源接手响应方法  
SplitDemoAppDelegate *_appDelegate;            //应用委托对象
ASIHTTPRequest *_httpRequest;            
UIImageView *_imageView;              
}
 
@property (nonatomic, retain) NSURL *resourceURL;
@property (nonatomic, retain) NSObject *hostObject;
@property (nonatomic, assign) SEL resourceDidReceive;
@property (nonatomic, assign) SplitDemoAppDelegate   *appDelegate;
@property (nonatomic, retain) ASIHTTPRequest *httpRequest;
@property (nonatomic, retain) UIImageView *imageView;
 
//http请求回调方法
-(void)didStartHttpRequest:(ASIHTTPRequest *)request;
-(void)didFinishHttpRequest:(ASIHTTPRequest *)request;
-(void)didFailedHttpRequest:(ASIHTTPRequest *)request;
 
//取消资源请求
-(void)cancelReourceGet;
//资源接收回调方法
-(void)resourceDidReceive:(NSData *)resource;
 
@end

    ResourceContainer.m文件实现：

#import "ResourceContainer.h"
#import "HttpConstant.h"
#import "ASIDownloadCache.h"
 
@implementation ResourceContainer
 
@synthesize resourceURL = _resourceURL;
@synthesize hostObject = _hostObject;
@synthesize resourceDidReceive = _resourceDidReceive;
@synthesize appDelegate = _appDelegate;
@synthesize httpRequest = _httpRequest;
@synthesize imageView = _imageView;
 
-(id)init{
if(self == [super init]){
self.appDelegate = (SplitDemoAppDelegate *)[[UIApplication sharedApplication] delegate];
}
return self;
}
 
-(void)main{
if(self.hostObject == nil)
return;
if(self.resourceURL == nil){
[self resourceDidReceive:nil];
return;
}
 
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:self.resourceURL];
self.httpRequest = request;
[self.httpRequest setDownloadCache:self.appDelegate.downloadCache];
[self.httpRequest setDelegate:self];
[self.httpRequest setDidStartSelector:@selector(didStartHttpRequest:)];
[self.httpRequest setDidFinishSelector:@selector(didFinishHttpRequest:)];
[self.httpRequest setDidFailSelector:@selector(didFailedHttpRequest:)];
    //发异步请求
[self.httpRequest startAsynchronous];
}
 
- (void)dealloc {
[_resourceURL release];
[_hostObject release];
[_httpRequest release];
[_imageView release];
    [super dealloc];
}
 
//开始请求
-(void)didStartHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
}
//请求成功返回处理结果
-(void)didFinishHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
 
    if([request responseStatusCode] == 200 || [request responseStatusCode] == 304){
//判断是否来自缓存
        if([request didUseCachedResponse]){
NSLog(@"=========资源请求：%@ 来自缓存============",[self.resourceURL absoluteURL]);
        }else{
            NSLog(@"=========资源请求：图片不来自缓存============");
        }
[self resourceDidReceive:[request responseData]];
}else {
[self resourceDidReceive:nil];
    }
}
//失败请求返回处理结果
-(void)didFailedHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
[self resourceDidReceive:nil];
}
//取消资源请求
-(void)cancelReourceGet{
[self.httpRequest cancel];
}
//资源接收处理方法
-(void)resourceDidReceive:(NSData *)resource{
if([self.hostObject respondsToSelector:self.resourceDidReceive]){
if(resource != nil && self.imageView != nil){
self.imageView.image = [UIImage imageWithData:resource];
}
 
[self.hostObject performSelectorOnMainThread:self.resourceDidReceive withObject:self.imageViewwaitUntilDone:NO];
}
}
 
@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，

 

#import <UIKit/UIKit.h>
@interface DetailViewController :UIViewController {
 
    NSURL                          *_imageURL;                    //图片url
    NSMutableArray            *_originalIndexArray;        //保存请求图片的号
    NSMutableDictionary     *_originalOperationDic;     //保存图片请求队列
    NSOperationQueue        *_requestImageQueue;    //图片请求队列
 
}

@property (nonatomic, retain) NSURL                        *imageURL;
@property (nonatomic, retain) NSMutableArray          *originalIndexArray;
@property (nonatomic, retain) NSMutableDictionary   *originalOperationDic;
@property (nonatomic, retain) NSOperationQueue      * requestImageQueue;
 
//显示图片信息
-(void)displayProductImage;
//根据图片序号显示请求图片资源
-(void)displayImageByIndex:(NSInteger)index ByImageURL:(NSURL *)url;
 
//处理图片请求返回信息
-(void)imageDidReceive:(UIImageView *)imageView;
 
@end

     在DetailViewController.m实现文件中，

 

 

#import "ProductDetailViewController.h"
//这里引入在第二步中，我们创建的对象
#import "ResourceContainer.h"

@implementation DetailViewController
 
@synthesize imageURL = _imageURL;
 
@synthesize originalIndexArray = _originalIndexArray;
@synthesize originalOperationDic = _originalOperationDic;
@synthesize requestImageQueue = _requestImageQueue;
 

- (void)viewDidLoad
{
     [super viewDidLoad];
     
     NSOperationQueue *tempQueue = [[NSOperationQueue alloc] init];
     self.requsetImageQueue = tempQueue;
     [tempQueue release];
 
      NSMutableArray *array = [[NSMutableArray alloc] init];
      self.originalIndexArray = array;
      [array release];
 
       NSMutableDictionary *dic = [[NSMutableDictionary alloc] init];
       self.originalOperationDic = dic;
       [dic release];
}
 
//显示图片信息
-(void)displayProductImage
{
    NSURL *url = [NSURL URLWithString:@"http://xxx.xxx.xxx.xxx"];
 
    //这个是从器返回有图片数目，self.xxxx根据具体的场合
    int imageCount = [self.xxxx.imageNum intValue];
 
    for (int i=0; i<imageCount; i++) {
        NSString *str1 = @"这里是拼图片请求url，根据实际需求";
        self.imageURL = [url URLByAppendingPathComponent:str1];
        //根据图片号请求资源
        [self displayImageByIndex:i ByImageURL:self.productImageURL];
    }
}
 
//根据图片序号显示请求图片资源
-(void) displayImageByIndex:(NSInteger)index ByImageURL:(NSURL *)url
{
    NSString *indexForString = [NSString stringWithFormat:@"%d",index];
    //若数组中已经存在该图片编号，说明图片加载完毕，直接返回
    if ([self.originalIndexArray containsObject:indexForString]) {
         return;
    }
    //创建UIImageView对象
    UIImageView *imageView = [[UIImageView alloc] init];
    imageView.tag = index;
    //创建资源请求对象
    ResourceContainer  *imageOperation = [[ResourceContainer alloc] init];
    imageOperation.resourceURL = url;
    imageOperation.hostObject = self;
    //设置收到图片信息处理理方法
    imageOperation.resourceDidReceive = @selector(imageDidReceive:);
    imageOperation.imageView = imageView;
    [imageView release];
    //将图片请求对象加入图片请求队列中
    [self.requsetImageQueue addOperation:imageOperation];
    [self.originalOperationDic setObject:imageOperation forKey:indexForString];
    [imageOperation release];
}
 
//处理图片请求返回信息
-(void)imageDidReceive:(UIImageView *)imageView
{
    if (imageView == nil||imageView.image == nil) {
            imageView.image = [UIImage imageNamed:@"no-pic-300-250.png"];
     }
 
    //将图片信息加载到前台，self.openFlowView是我用的coverFlow，coverFlow的使用方法网上很多，自己找吧
    [self.openFlowView setImage:imageView.image forIndex:imageView.tag];
    [self.originalIndexArray addObject:[NSString stringWithFormat:@"%d",imageView.tag]];
    [self.originalOperationDic removeObjectForKey:[NSString stringWithFormat:@"%d",imageView.tag]];
 
}
 
- (void)dealloc
{
     [_requestImageQueue release];
     [_originalIndexArray release];
     [_originalOperationDic release];
     [_imageURL release];
 
     [super dealloc];
}
 
@end

 文章转载自：http://blog.csdn.net/pjk1129/article/details/6574280