ios 图片的网络下载和显示（可缓存）

思路是：已存在的图片则从本地读取，本地不存在的图片则从网上下载到本地

在这里下载图片使用的是ASIHTTPRequest，

asi-http-request的使用参考：http://blog.csdn.net/marujunyy/article/details/8474518

下面是用法和自己写的一个类的代码：

现在需要使用它的类的.h文件中添加delegate，如下：

#import <UIKit/UIKit.h>#import "AsyncImageView.h"@interface RelatedAppsUIView : UIView<AsyncImageDelegate>{        __weak IBOutlet UIImageView *appImageView;}@end

然后在使用它的类的.m文件中添加代理的方法，如下：

#import "RelatedAppsUIView.h"@implementation RelatedAppsUIView-(void)awakeFromNib{    AsyncImageView *asyncImageView=[[AsyncImageView alloc] init];    //如果有多个图片，则添加tag        asyncImageView.delegate=self;    asyncImageView.tag=1001;    [asyncImageView loadImageFromURL:[NSURL URLWithString:[@"http://csdnimg.cn/www/images/csdnindex_logo.gif" stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];}#pragma mark - AsyncImageDelegate-(void)getImageSuccess:(UIImage *)image tag:(NSNumber *)tag{    NSLog(@"tag ->>%@",tag);    appImageView.image=image;}-(void)getImageFail:(UIImage *)image tag:(NSNumber *)tag{    //TUDO 添加默认图片  错误返回}@end

下面是类：AsyncImageView的.h和.m文件的代码

//  AsyncImageView.h#import <Foundation/Foundation.h>#import <UIKit/UIKit.h>#import "ASIFormDataRequest.h"@protocol AsyncImageDelegate <NSObject>-(void)getImageSuccess:(UIImage *)image tag:(NSNumber *)tag;-(void)getImageFail:(UIImage *)image tag:(NSNumber *)tag;@end@interface AsyncImageView : NSObject <ASIHTTPRequestDelegate>{    NSURL *urls;    id<AsyncImageDelegate> delegate;    int tag;}@property (nonatomic,assign) int tag;@property (nonatomic,retain)  id<AsyncImageDelegate> delegate;- (void)loadImageFromURL:(NSURL*)url;//-(NSString *)GetTempPath:(NSString*)filename;-(BOOL)isExistsFile:(NSString *)filepath;-(UIImage *)getImage:(NSString*)filename;-(void)writeDataToFile:(NSString*)filename fileData:(NSData *)fileData;-(NSString *) getCacheFilePath:(NSString *)filename;@end

//  AsyncImageView.m#import "AsyncImageView.h"@implementation AsyncImageView@synthesize delegate,tag;- (void)dealloc {    [delegate release];    //    //NSLog(@"AsyncImageView delloc");    [super dealloc];}- (void)loadImageFromURL:(NSURL*)url {//    NSLog(@"--loadImageFromURL>>%@",url);    if(url!=nil&&![url isEqual:@""]) {        if ([self isExistsFile:[url description]]) {            //返回数据             if ([delegate respondsToSelector:@selector(getImageSuccess:tag:)]) {                [delegate performSelector:@selector(getImageSuccess:tag:) withObject:[self getImage:[url description]] withObject:[NSNumber numberWithInt:self.tag]];            }        }else{            urls=url;            [self retain];            ASIHTTPRequest *request = [[[ASIHTTPRequest alloc] initWithURL:urls] autorelease];            [request setDelegate:self];            [request startAsynchronous];        }    }}-(void)requestFailed:(ASIHTTPRequest *)request{    if ([delegate respondsToSelector:@selector(getImageFail:tag:)]) {        [delegate performSelector:@selector(getImageFail:tag:) withObject:nil withObject:[NSNumber numberWithInt:self.tag]];    }    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;    [self release];}- (void)requestFinished:(ASIHTTPRequest *)request{    NSData *responseData = [request responseData];    UIImage *image=[UIImage imageWithData:responseData];    if (image!=nil) {        [self writeDataToFile:[urls description] fileData:responseData];        if ([delegate respondsToSelector:@selector(getImageSuccess:tag:)]) {            [delegate performSelector:@selector(getImageSuccess:tag:) withObject:image withObject:[NSNumber numberWithInt:self.tag]];        }    }else{        if ([delegate respondsToSelector:@selector(getImageFail:tag:)]) {            [delegate performSelector:@selector(getImageFail:tag:) withObject:image withObject:[NSNumber numberWithInt:self.tag]];        }    }    [self release];}-(BOOL)isExistsFile:(NSString *)filepath{    NSFileManager *filemanage = [NSFileManager defaultManager];    NSArray *array=[filepath componentsSeparatedByString:@"//"];    NSArray *arrayName=[filepath componentsSeparatedByString:@"/"];    NSString *file=[NSString stringWithFormat:@"%@/%@",[array lastObject],[arrayName lastObject]];    return [filemanage fileExistsAtPath:[self getCacheFilePath:file]];}-(UIImage *)getImage:(NSString*)filename{    NSArray *array=[filename componentsSeparatedByString:@"//"];    NSArray *arrayName=[filename componentsSeparatedByString:@"/"];    NSString *file=[NSString stringWithFormat:@"%@/%@",[array lastObject],[arrayName lastObject]];    UIImage *image=[UIImage imageWithData:[NSData dataWithContentsOfFile:[self getCacheFilePath:file]]];    return image;}-(NSString *) getCacheFilePath:(NSString *)filename{NSArray *paths=NSSearchPathForDirectoriesInDomains(NSCachesDirectory,NSUserDomainMask,YES);NSString *path=[paths objectAtIndex:0];NSString *filePath=[path stringByAppendingPathComponent:filename];return filePath;}-(void)writeDataToFile:(NSString*)filename fileData:(NSData *)fileData{    NSArray *array=[filename componentsSeparatedByString:@"//"];    [[NSFileManager defaultManager] createDirectoryAtPath:[self getCacheFilePath:[array lastObject]] withIntermediateDirectories:YES attributes:nil error:nil];    NSArray *arrayName=[filename componentsSeparatedByString:@"/"];    NSString *file=[NSString stringWithFormat:@"%@/%@",[array lastObject],[arrayName lastObject]];    [fileData writeToFile:[self getCacheFilePath:file] atomically:YES];}@end