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一: 利用NSFileHandle对象实现大文件下载

 1.要了解NSFileHandle的用法，注意下载完要关闭这个对象。还要记得每次写入之前将它的文件指针挪位！

////  ViewController.m//  多值参数////  Created by Mac on 16/1/23.//  Copyright © 2016年 Mac. All rights reserved.//#define ZZFile  [ [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingString:@"minion_15.mp4"]#import "ViewController.h"@interface ViewController ()
     
      @property (weak, nonatomic) IBOutlet UIProgressView *proView;//@property (nonatomic, strong) NSMutableData *fileData;@property (nonatomic, assign) NSInteger contentLength;@property (nonatomic, assign) NSInteger currentLength;@property (nonatomic, strong) NSFileHandle *handle;//@property (nonatomic, strong) UIImage *image;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    //  这种方法没法暂停，只适合下载小文件        NSURL *url = [[NSURL alloc] initWithString:@"http://120.25.226.186:32812/resources/videos/minion_15.mp4" ];    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];    // 设置connect的代理    [NSURLConnection connectionWithRequest:request delegate:self];}#pragma mark - NSURLConnect 的代理// connection接收到响应,此时应当创建数据准备拼接data- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSHTTPURLResponse *)response{    NSHTTPURLResponse *newResponse = response;        // 获得文件的总长度    self.contentLength = [newResponse.allHeaderFields[@"Content-Length"] integerValue];    // 创建一个空的文件    [[NSFileManager defaultManager] createFileAtPath:ZZFile contents:nil attributes:nil];        self.handle = [NSFileHandle fileHandleForWritingAtPath:ZZFile];}// 接收到了数据，这个方法会被多次调用，需要在这里拼接数据- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{// 接收到数据后写入文件    // 设置当前下载量    self.currentLength += data.length;        // 制定文件的写入位置，在当前文件的最后面    [self.handle seekToEndOfFile];        // 写入数据    [self.handle writeData:data];        self.proView.progress = 1.0 * self.currentLength / self.contentLength;    }// 下载完成- (void)connectionDidFinishLoading:(NSURLConnection *)connection{    // 下载完毕后需要关闭handle    [self.handle closeFile];        self.handle = nil;        self.currentLength = 0;    }@end