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// // FileDownload.h // 01.文件下载 // // Created by wyh on 15-1-29. // Copyright (c) 2015年 itcast. All rights reserved. // #import <Foundation/Foundation.h> @interface FileDownload : NSObject - (void)downloadFileWithURL:(NSURL *)url completion:(void (^)(UIImage *image))completion; @end
// // FileDownload.m // 01.文件下载 // // Created by wyh on 15-1-29. // Copyright (c) 2015年 itcast. All rights reserved. // #import "FileDownload.h" #import "NSString+Password.h" #define kTimeOut 2.0f // 每次下载的字节数 #define kBytesPerTimes 20250 @interface FileDownload() @property (nonatomic, strong) NSString *cacheFile; @property (nonatomic, strong) UIImage *cacheImage; @end @implementation FileDownload /** 为了保证开发的简单,所有方法都不使用多线程,所有的注意力都保持在文件下载上 在开发中如果碰到比较绕的计算问题时,建议: 1> 测试数据不要太大 2> 测试数据的数值变化,能够用笔算计算出准确的数值 3> 编写代码对照测试 */ //- (NSString *)cacheFile //{ // if (!_cacheFile) { // NSString *cacheDir = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0]; // _cacheFile = [cacheDir stringByAppendingPathComponent:@"123.png"]; // } // return _cacheFile; //} - (UIImage *)cacheImage { if (!_cacheImage) { _cacheImage = [UIImage imageWithContentsOfFile:self.cacheFile]; } return _cacheImage; } - (void)setCacheFile:(NSString *)urlStr { NSString *cacheDir = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0]; urlStr = [urlStr MD5]; _cacheFile = [cacheDir stringByAppendingPathComponent:urlStr]; } - (void)downloadFileWithURL:(NSURL *)url completion:(void (^)(UIImage *image))completion { // GCD中的串行队列异步方法 dispatch_queue_t q = dispatch_queue_create("cn.itcast.download", DISPATCH_QUEUE_SERIAL); dispatch_async(q, ^{ NSLog(@"%@", [NSThread currentThread]); // 把对URL进行MD5加密之后的结果当成文件名 self.cacheFile = [url absoluteString]; // 1. 从网络下载文件,需要知道这个文件的大小 long long fileSize = [self fileSizeWithURL:url]; // 计算本地缓存文件大小 long long cacheFileSize = [self localFileSize]; if (cacheFileSize == fileSize) { dispatch_async(dispatch_get_main_queue(), ^{ completion(self.cacheImage); }); NSLog(@"文件已经存在"); return; } // 2. 确定每个数据包的大小 long long fromB = 0; long long toB = 0; // 计算起始和结束的字节数 while (fileSize > kBytesPerTimes) { // 20480 + 20480 // toB = fromB + kBytesPerTimes - 1; // 3. 分段下载文件 [self downloadDataWithURL:url fromB:fromB toB:toB]; fileSize -= kBytesPerTimes; fromB += kBytesPerTimes; } [self downloadDataWithURL:url fromB:fromB toB:fromB + fileSize - 1]; dispatch_async(dispatch_get_main_queue(), ^{ completion(self.cacheImage); }); }); } #pragma mark 下载指定字节范围的数据包 /** NSURLRequestUseProtocolCachePolicy = 0, // 默认的缓存策略,内存缓存 NSURLRequestReloadIgnoringLocalCacheData = 1, // 忽略本地的内存缓存 NSURLRequestReloadIgnoringCacheData */ - (void)downloadDataWithURL:(NSURL *)url fromB:(long long)fromB toB:(long long)toB { NSLog(@"数据包:%@", [NSThread currentThread]); NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:kTimeOut]; // 指定请求中所要GET的字节范围 NSString *range = [NSString stringWithFormat:@"Bytes=%lld-%lld", fromB, toB]; [request setValue:range forHTTPHeaderField:@"Range"]; NSLog(@"%@", range); NSURLResponse *response = nil; NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL]; // 写入文件,覆盖文件不会追加 // [data writeToFile:@"/Users/aplle/Desktop/1.png" atomically:YES]; [self appendData:data]; NSLog(@"%@", response); } #pragma mark - 读取本地缓存文件大小 - (long long)localFileSize { // 读取本地文件信息 NSDictionary *dict = [[NSFileManager defaultManager] attributesOfItemAtPath:self.cacheFile error:NULL]; NSLog(@"%lld", [dict[NSFileSize] longLongValue]); return [dict[NSFileSize] longLongValue]; } #pragma mark - 追加数据到文件 - (void)appendData:(NSData *)data { // 判断文件是否存在 NSFileHandle *fp = [NSFileHandle fileHandleForWritingAtPath:self.cacheFile]; // 如果文件不存在创建文件 if (!fp) { [data writeToFile:self.cacheFile atomically:YES]; } else { // 如果文件已经存在追加文件 // 1> 移动到文件末尾 [fp seekToEndOfFile]; // 2> 追加数据 [fp writeData:data]; // 3> 写入文件 [fp closeFile]; } } #pragma mark - 获取网络文件大小 - (long long)fileSizeWithURL:(NSURL *)url { // 默认是GET NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:0 timeoutInterval:kTimeOut]; // HEAD 头,只是返回文件资源的信息,不返回具体是数据 // 如果要获取资源的MIMEType,也必须用HEAD,否则,数据会被重复下载两次 request.HTTPMethod = @"HEAD"; // 使用同步方法获取文件大小 NSURLResponse *response = nil; [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL]; // expectedContentLength文件在网络上的大小 NSLog(@"%lld", response.expectedContentLength); return response.expectedContentLength; } @end
// // ViewController.m // 01.文件下载 // // Created by wyh on 15-1-29. // Copyright (c) 2015年 itcast. All rights reserved. // #import "ViewController.h" #warning 包含FileDownload.h文件 #import "FileDownload.h" @interface ViewController () @property (nonatomic, strong) FileDownload *download; @property (weak, nonatomic) IBOutlet UIImageView *imageView; @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; #warning 创建FileDownload对象,并调用方法downloadFileWithURL: self.download = [[FileDownload alloc] init]; [self.download downloadFileWithURL:[NSURL URLWithString:@"http://localhost/itcast/images/head4.png"] completion:^(UIImage *image) { self.imageView.image = image; }]; } @end
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原文地址:http://www.cnblogs.com/wangyinghui/p/4356711.html