//
//  YWebDownManager.h
//  WebImageDemo
//
//  Created by YueWen on 16/3/20.
//  Copyright © 2016年 YueWen. All rights reserved.
//#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>/***  下载成功后的回调**  @param path  下载成功在本地的路径*/
typedef void(^DownManagerFinishBlock)(NSString * path);/***  下载过程中的回调**  @param didFinish      本次下载的文件大小*  @param didFinishTotal 至此一共下载文件的大小*  @param Total          一共需要下载文件的大小*/
typedef void(^DownManagerProgressBlock)(CGFloat didFinish,CGFloat didFinishTotal,CGFloat Total);NS_CLASS_AVAILABLE_IOS(7_0) @interface YWebDownManager : NSObject//开始下载图片
- (void)startDownImagePath:(NSString *)imagePath NS_AVAILABLE_IOS(7_0);
- (void)startDownImageURL:(NSURL *)imageURL NS_AVAILABLE_IOS(7_0);//设置相关回调
- (void)downManagerFinishBlockHandle:(DownManagerFinishBlock)downManagerFinishBlockHandle;
- (void)downManagerProgressBlockHandle:(DownManagerProgressBlock)downManagerProgressBlockHandle;@end

实现方法:

@interface YWebDownManager ()<NSURLSessionDownloadDelegate>@property (nonatomic, copy)NSString * imagePath;        //记录图片url的字符串path
@property (nonatomic, copy)NSURL * imageURL;            //请求图片的url
@property (nonatomic, copy)NSString * imageName;        //转型后的图片名称
@property (nonatomic, copy)NSString * documentPath;     //沙盒路径@property (nonatomic, copy)DownManagerFinishBlock finishBlockHandle;        //下载完成后的回调
@property (nonatomic, copy)DownManagerProgressBlock progressBlockHandle;    //下载过程中的回调@end

设置回调的方法就是一个简单赋值的过程，不需要多说了

#pragma mark - 设置回调的方法
-(void)downManagerFinishBlockHandle:(DownManagerFinishBlock)downManagerFinishBlockHandle
{self.finishBlockHandle = downManagerFinishBlockHandle;
}-(void)downManagerProgressBlockHandle:(DownManagerProgressBlock)downManagerProgressBlockHandle
{self.progressBlockHandle = downManagerProgressBlockHandle;
}

实现两个getter方法，方便取值，一个依旧是获得沙盒路径，另一个就是获得转型base64字符串的图片名称，在本地存储的图片名就是这个字符串，为什么需要转换呢，我们很多时候看到缓存的图片是不是名字特别长呢，是因为害怕图片名字上会有难识别的特殊字符，所以需要base64来转换一下。

#pragma mark - Document Path
- (NSString *)documentPath
{return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, true) firstObject];
}#pragma mark - Image Name Base64
-(NSString *)imageName
{return [YWebDataHandle imageNameForBase64Handle:_imageURL.absoluteString];
}

接着开始用NSURLSession进行下载:这里会和NSURLConnection相似，因为习惯用AFNetworking，但不得不说这个第三方对于网络请求，着实强大，并且2.0版本也已经对之前的代码进行了重构，用NSURLSession代替了之前的NSURLConnection，但是楼主还是推荐看一下原生的类，拓展一下视野。

#pragma mark - 开始下载图片的方法
-(void)startDownImagePath:(NSString *)imagePath
{NSLog(@"开始下载图片啦,路径为:%@",imagePath);//赋值_imagePath = imagePath;//创建url对象NSURL * downURL = [[NSURL alloc]initWithString:_imagePath];//开始根据URL请求图片[self startDownImageURL:downURL];}- (void)startDownImageURL:(NSURL *)imageURL
{//开始赋值_imageURL = imageURL;//创建请求对象NSURLRequest * request = [NSURLRequest requestWithURL:_imageURL];//创建网络请求对象NSURLSession * session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:nil];//获取下载对象NSURLSessionDownloadTask * downLoadTask = [session downloadTaskWithRequest:request];//开始请求[downLoadTask resume];
}

实现代理方法,主要就是往本地存以及往外传值得一个过程:

#pragma mark - NSURLSessionDownload Delegate//下载完成
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{//路径字符串NSString * path = [NSString stringWithFormat:@"%@/YWebImageFile/%@",self.documentPath,self.imageName];//获取创建下载到的路径urlNSURL * url = [NSURL fileURLWithPath:path];//获取文件管理者NSFileManager * fileManager = [NSFileManager defaultManager];//存到文件[fileManager moveItemAtURL:location toURL:url error:nil];//主线程回调dispatch_async(dispatch_get_main_queue(), ^{//执行回调,传出路径if (self.finishBlockHandle) {self.finishBlockHandle(path);}});
}- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTaskdidWriteData:(int64_t)bytesWrittentotalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{//主线程进行回调dispatch_async(dispatch_get_main_queue(), ^{//执行过程的回调if (self.progressBlockHandle) {self.progressBlockHandle(bytesWritten,totalBytesWritten,totalBytesExpectedToWrite);}});
}

YWebDataHandle

NS_AVAILABLE_IOS(7_0) @interface YWebDataHandle : NSObject/***  将路径或者url转成base64处理的字符串**  @param path 需要处理的字符串**  @return 处理完毕的字符串*/
+ (NSString *)imageNameForBase64Handle:(NSString *)path;@end@implementation YWebDataHandle+(NSString *)imageNameForBase64Handle:(NSString *)path
{NSData * data = [path dataUsingEncoding:NSUTF8StringEncoding];NSString * imageNameBase = [data base64EncodedStringWithOptions:0];return [imageNameBase substringToIndex:imageNameBase.length - 2];
}@end

UIImageView + YWebImage

#import <UIKit/UIKit.h>/***  下载过程中的回调**  @param didFinish      本次下载的文件大小*  @param didFinishTotal 至此一共下载文件的大小*  @param Total          一共需要下载文件的大小*/
typedef void(^DownManagerProgressBlock)(CGFloat didFinish,CGFloat didFinishTotal,CGFloat Total);@interface UIImageView (YWebImage)//根据url设置图片
- (void)yw_setImageWithUrl:(NSString *)url;- (void)yw_setImageWithUrl:(NSString *)urlwithProgressHandle:(DownManagerProgressBlock)progresshandle;//根据url设置图片，并支持默认占位图
- (void)yw_setImageWithUrl:(NSString *)urlplaceHolderImage:(UIImage *)placeHodlerImage;- (void)yw_setImageWithUrl:(NSString *)urlplaceHolderImage:(UIImage *)placeHodlerImagewithProgressHandle:(DownManagerProgressBlock)progresshandle;@end

实现方法完成四个即可，看似是四个，有经验的人一看也就知道其实只实现一个即可，其他的调用主方法即可:

-(void)yw_setImageWithUrl:(NSString *)urlwithProgressHandle:(DownManagerProgressBlock)progresshandle
{//处理urlNSString * urlHandle = [YWebDataHandle imageNameForBase64Handle:url];//本地查询if([[YWebFileManager shareInstanceType] fileIsExist:urlHandle])//如果本地存在返回图片{NSLog(@"本地已经存在这个图片了!");self.image = [[YWebFileManager shareInstanceType] imageWithURL:urlHandle];}//不存在需要根据url下载else{NSLog(@"本地没有这个图片!");//开始下载[self downImage:url withProgressHandle:progresshandle];}
}

其它的三调用此方法即可：

{[self yw_setImageWithUrl:url withProgressHandle:^(CGFloat didFinish, CGFloat didFinishTotal, CGFloat Total) {}];
}- (void)yw_setImageWithUrl:(NSString *)url placeHolderImage:(UIImage *)placeHodlerImage
{[self yw_setImageWithUrl:url placeHolderImage:placeHodlerImage withProgressHandle:^(CGFloat didFinish, CGFloat didFinishTotal, CGFloat Total) {}];
}- (void)yw_setImageWithUrl:(NSString *)url placeHolderImage:(UIImage *)placeHodlerImage withProgressHandle:(DownManagerProgressBlock)progresshandle
{//设置占位图self.image = placeHodlerImage;//开始设置图片[self yw_setImageWithUrl:url withProgressHandle:progresshandle];
}

因为下载过程代码比较多，依照楼主的习惯还是拿出来当成一个方法:

//开始下载图片
- (void)downImage:(NSString *)url
{[self downImage:url withProgressHandle:^(CGFloat didFinish, CGFloat didFinishTotal, CGFloat Total) {}];
}//开始下载图片
- (void)downImage:(NSString *)url
withProgressHandle:(DownManagerProgressBlock)progresshandle
{YWebDownManager * webDownManager = [[YWebDownManager alloc]init];//开始下载[webDownManager startDownImagePath:url];//设置下载完毕的回调[webDownManager downManagerFinishBlockHandle:^(NSString *path) {//获得当前的图片对象UIImage * image = [UIImage imageWithContentsOfFile:path];self.image = image;}];//设置下载过程的回调[webDownManager downManagerProgressBlockHandle:^(CGFloat didFinish, CGFloat didFinishTotal, CGFloat Total) {//进行回调progresshandle(didFinish,didFinishTotal,Total);}];
}