IOS开发网络加载图片缓存策略之──ASIDownloadCache缓存策略
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 <UIKit/UIKit.h>
2
3 @class ASIDownloadCache;
4
5 @interface SplitDemoAppDelegate : NSObject <UIApplicationDelegate,UITabBarControllerDelegate> {
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 <Foundation/Foundation.h>
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：
ResourceContainer
resourceURL = _resourceURL;
hostObject = _hostObject;
resourceDidReceive = _resourceDidReceive;
appDelegate = _appDelegate;
httpRequest = _httpRequest;
imageView = _imageView;
-()init{
(self == [super init]){
self.appDelegate = (SplitDemoAppDelegate *)[[UIApplication sharedApplication] ];
}
self;
}
-()main{
(self.hostObject == nil)
;
(self.resourceURL == nil){
[self resourceDidReceive:nil];
;
}
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:)];
[self.httpRequest startAsynchronous];
}
- ()dealloc {
[_resourceURL release];
[_hostObject release];
[_httpRequest release];
[_imageView release];
[super dealloc];
}
-()didStartHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
}
-()didFinishHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
([request responseStatusCode] == || [request responseStatusCode] == ){
([request didUseCachedResponse]){
NSLog(,[self.resourceURL absoluteURL]);
}
{
NSLog();
}
[self resourceDidReceive:[request responseData]];
}
{
[self resourceDidReceive:nil];
}
}
-()didFailedHttpRequest:(ASIHTTPRequest *)request{
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
[self resourceDidReceive:nil];
}
-()cancelReourceGet{
[self.httpRequest cancel];
}
-()resourceDidReceive:(NSData *)resource{
([self.hostObject respondsToSelector:self.resourceDidReceive]){
(resource != nil && self.imageView != nil){
self.imageView.image = [UIImage imageWithData:resource];
}
[self.hostObject performSelectorOnMainThread:self.resourceDidReceive withObject:self.imageViewwaitUntilDone:NO];
}
}
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:
<UIKit/UIKit.h>
DetailViewController :UIViewController {
NSURL *_imageURL;
NSMutableArray *_originalIndexArray;
NSMutableDictionary *_originalOperationDic;
NSOperationQueue *_requestImageQueue;
}
@property (nonatomic, retain) NSURL *imageURL;
@property (nonatomic, retain) NSMutableArray *originalIndexArray;
@property (nonatomic, retain) NSMutableDictionary *originalOperationDic;
@property (nonatomic, retain) NSOperationQueue * requestImageQueue;
-()displayProductImage;
-()displayImageByIndex:(NSInteger)index ByImageURL:(NSURL *)url;
-()imageDidReceive:(UIImageView *)imageView;
在DetailViewController.m实现文件中:
DetailViewController
imageURL = _imageURL;
originalIndexArray = _originalIndexArray;
originalOperationDic = _originalOperationDic;
requestImageQueue = _requestImageQueue;
- ()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];
}
-()displayProductImage
{
NSURL *url = [NSURL URLWithString:];
imageCount = [self.xxxx.imageNum intValue];
( i=; i<imageCount; i++) {
NSString *str1 = ;
self.imageURL = [url URLByAppendingPathComponent:str1];
[self displayImageByIndex:i ByImageURL:self.productImageURL];
}
}
-() displayImageByIndex:(NSInteger)index ByImageURL:(NSURL *)url
{
NSString *indexForString = [NSString stringWithFormat:,index];
([self.originalIndexArray containsObject:indexForString]) {
;
}
UIImageView *imageView = [[UIImageView alloc] init];
imageView.tag = index;
ResourceContainer *imageOperation = [[ResourceContainer alloc] init];
imageOperation.resourceURL = url;
imageOperation.hostObject = self;
imageOperation.resourceDidReceive = @selector(imageDidReceive:);
imageOperation.imageView = imageView;
[imageView release];
[self.requsetImageQueue addOperation:imageOperation];
[self.originalOperationDic setObject:imageOperation forKey:indexForString];
[imageOperation release];
}
-()imageDidReceive:(UIImageView *)imageView
{
(imageView == nil||imageView.image == nil) {
imageView.image = [UIImage imageNamed:];
}
[self.openFlowView setImage:imageView.image forIndex:imageView.tag];
[self.originalIndexArray addObject:[NSString stringWithFormat:,imageView.tag]];
[self.originalOperationDic removeObjectForKey:[NSString stringWithFormat:,imageView.tag]];
}
- ()dealloc
{
[_requestImageQueue release];
[_originalIndexArray release];
[_originalOperationDic release];
[_imageURL release];
[super dealloc];
}
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！