前言

1. 無論是NSURLConnection還是NSURLSession要實(shí)現(xiàn)斷點(diǎn)續(xù)傳,原理都差不多:記錄下載位置,下次開始下載的時(shí)候帶著該位置請(qǐng)求網(wǎng)絡(luò)即可.
2. 下面只介紹下NSURLSession的斷點(diǎn)續(xù)傳,文章末尾的demo里NSURLConnection和NSURLSession都實(shí)現(xiàn)了斷點(diǎn)續(xù)傳,大家可以自取.

封裝了一個(gè)類,演示下實(shí)現(xiàn)過程,上代碼

//
//  YYSessionVC.m
//  文件下載(可斷點(diǎn)續(xù)傳)
//
//  Created by yyMae on 16/1/21.
//  Copyright (c) 2016年 yyMae. All rights reserved.
//

#import "YYSessionVC.h"

@interface YYSessionVC ()<NSURLSessionDownloadDelegate>
//顯示下載進(jìn)度
@property (nonatomic, strong) UIProgressView *progressView;
@property (nonatomic, strong) UILabel *progressL;

@property (nonatomic, strong) NSURLSessionDownloadTask *downloadTask;//下載任務(wù)
@property (nonatomic, strong) NSData *resumeData;//記錄下載位置
@property (nonatomic, strong) NSURLSession *session;

@property (nonatomic, strong) UIButton *button;
@end

@implementation YYSessionVC

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    self.title = @"NSURLSession";
    [self addView];
    //NSLog(@"%@",NSHomeDirectory());
}

- (void)addView{
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    button.frame = CGRectMake(0, 0, 200, 20);
    button.center = CGPointMake(self.view.frame.size.width * 0.5, 250);
    [button setTitle:@"download" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(download1:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
    self.button = button;
    UIProgressView *progressView = [[UIProgressView alloc]initWithFrame:CGRectMake(0, 0, 200, 20)];
    progressView.center = CGPointMake(self.view.frame.size.width * 0.5, 150);
    [self.view addSubview:progressView];
    self.progressView = progressView;
    UILabel *progressL = [[UILabel alloc]initWithFrame:CGRectMake(0, 0, 200, 20)];
    progressL.center = CGPointMake(progressView.center.x, 190);
    progressL.text = @"下載進(jìn)度:0.000000";
    [self.view addSubview:progressL];
    self.progressL = progressL;
}

/**
 *  session懶加載
 *
 *  @return session
 */
-(NSURLSession *)session{
    if (_session == nil) {
        //??????
        NSURLSessionConfiguration *cfg = [NSURLSessionConfiguration defaultSessionConfiguration];
        _session = [NSURLSession sessionWithConfiguration:cfg delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    }
    return _session;
}

//從0開始下載
- (void)start{
    //conerstone下載地址
    NSURL* url = [NSURL URLWithString:@"http://att4.weiphone.net/temp16/201405/06/7/Cornerstone_v2.7.10.dmg"];
    //創(chuàng)建下載任務(wù)
    self.downloadTask = [self.session downloadTaskWithURL:url];
    //開始任務(wù)
    [self.downloadTask resume];
}

//繼續(xù)下載
- (void)resume{
    //傳入上次暫停返回的數(shù)據(jù)
    self.downloadTask = [self.session downloadTaskWithResumeData:self.resumeData];
    //開始任務(wù)
    [self.downloadTask resume];
    
    self.resumeData = nil;
}

//暫停下載
- (void)pause{
    __weak typeof(self) selfVC = self;
    [self.downloadTask cancelByProducingResumeData:^(NSData *resumeData) {
        selfVC.resumeData = resumeData;
        selfVC.downloadTask = nil;
    }];
}
- (void)download1:(UIButton *)sender{
    sender.selected = !sender.isSelected;
    if (nil == self.downloadTask) {
        if (self.resumeData) {//繼續(xù)下載
            [self.button setTitle:@"暫停" forState:UIControlStateNormal];
            [self resume];
        }else{//開始下載
            [self.button setTitle:@"暫停" forState:UIControlStateNormal];
            [self start];
        }
    }else{//暫停下載
        [self.button setTitle:@"繼續(xù)" forState:UIControlStateNormal];
        [self pause];
    }
}

#pragma mark -- NSURLSessionDownloadDelegate
/**
 *  下載完成調(diào)用
 *
 *  @param session
 *  @param downloadTask
 *  @param location     文件臨時(shí)地址
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{
    //獲取文件路徑
    NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *filePath = [caches stringByAppendingPathComponent:downloadTask.response.suggestedFilename];
    //剪切文件到路徑
    NSFileManager *fm = [NSFileManager defaultManager];
    [fm moveItemAtPath:location.path toPath:filePath error:nil];
    //提示下載完成
    [[[UIAlertView alloc]initWithTitle:@"下載完成" message:downloadTask.response.suggestedFilename delegate:self cancelButtonTitle:@"知道了" otherButtonTitles: nil] show];
}

/**
 *  每次寫入沙盒完畢調(diào)用
 *
 *  @param session
 *  @param downloadTask
 *  @param bytesWritten              本次寫入大小
 *  @param totalBytesWritten         已經(jīng)寫入大小
 *  @param totalBytesExpectedToWrite 文件總大小
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
    //下載進(jìn)度
    self.progressView.progress = (double)totalBytesWritten / totalBytesExpectedToWrite;
    NSString *str = [NSString stringWithFormat:@"下載進(jìn)度:%f",(double)totalBytesWritten / totalBytesExpectedToWrite];
    self.progressL.text = str;
}

/**
 *  恢復(fù)下載時(shí)調(diào)用
 *
 *  @param session
 *  @param downloadTask
 *  @param fileOffset
 *  @param expectedTotalBytes
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes{
    
}

    

@end

demo下載地址
https://github.com/yyMae/download