依靠NSOutputStream,NSURLSession,NSURLSessionDataTask创建一个支持断点下载的任务

最新推荐文章于 2018-04-08 18:45:34 发布

战略观察者

最新推荐文章于 2018-04-08 18:45:34 发布

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CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/baohanqing/article/details/51179706

本文介绍了一个iOS应用中实现断点续传下载功能的方法。通过NSURLSessionDataDelegate接口，利用NSOutputStream进行文件写入，实现了从上次下载的位置继续下载的功能，并记录了已下载的数据量。此外，还介绍了如何使用plist文件保存文件的总大小，以便于下次启动应用时能够正确地显示进度。

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//
//  ViewController.m
//  BreakPointDownload
//
//  Created by hq on 16/4/18.
//  Copyright © 2016年 hanqing. All rights reserved.
//

#import "ViewController.h"
#import "NSString+Hash.h"

//定义文件等下载路径cache路径
#define HQFilePath NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject

#define HQFileURLString @"http://xxx/resources/videos/minion_01.mp4"


//定义我们的文件名,直接只用url因为每个url对应一个文件是唯一的
#define HQFileName HQFileURLString.md5String


@interface ViewController () <NSURLSessionDataDelegate>

@property (weak, nonatomic) IBOutlet UILabel *downloadStatus;
@property (weak, nonatomic) IBOutlet UIProgressView *pro;
@property (weak, nonatomic) IBOutlet UILabel *downSize;

@property (weak, nonatomic) IBOutlet UIButton *loadBut;

//文件等总大小
@property(nonatomic,assign) NSInteger fileTotalSize;
//当前文件下载了多少
@property(nonatomic,assign) NSInteger fileCurrentSize;


@property(nonatomic,strong) NSOutputStream *outputStream;

@property(nonatomic,strong) NSURLSessionDataTask *task;


- (IBAction)butClicked:(UIButton *)sender;

@property(nonatomic,strong) NSOperationQueue *queue;

@end

@implementation ViewController


-(NSURLSessionDataTask *)task{
    
    if (!_task) {
      
        NSURLSession *session=[NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc] init]];
        
        NSMutableURLRequest *request=[NSMutableURLRequest requestWithURL:[NSURL URLWithString:HQFileURLString]];
        
        //指定从哪个位置继续下载
        [request setValue:[NSString stringWithFormat:@"bytes=%ld-",[self getCurrentDownloadSize]] forHTTPHeaderField:@"Range"];
        
        _task=[session dataTaskWithRequest:request];
        
    }
    
    return _task;
}



-(NSOutputStream *)outputStream{
    
    if (!_outputStream) {
       
        _outputStream=[[NSOutputStream alloc]initToFileAtPath:[HQFilePath stringByAppendingPathComponent:HQFileName] append:YES];
    }
    return _outputStream;
}


- (void)viewDidLoad {
    [super viewDidLoad];

    
    NSString *plistPath=[HQFilePath stringByAppendingPathComponent:@"fileSize.plist"];
    
    //获取文件的总大小
    NSInteger totalSize=[[NSDictionary dictionaryWithContentsOfFile:plistPath][HQFileName] integerValue];
    
    if (totalSize==0) {
        self.downSize.hidden=YES;
        self.pro.progress=0;
    }
    else{
        self.downSize.hidden=NO;
        self.downSize.text=[NSString stringWithFormat:@"%.0f％",1.0*[self getCurrentDownloadSize]/totalSize*100];
        self.pro.progress=1.0*[self getCurrentDownloadSize]/totalSize;
    }

    
    if (totalSize==[self getCurrentDownloadSize]&&totalSize!=0) {
        
        self.downloadStatus.hidden=NO;
        
        self.loadBut.enabled=NO;
        
        [self.loadBut setTitle:@"开始下载" forState:UIControlStateNormal];
        
    }
    
    NSLog(@"%@",[HQFilePath stringByAppendingPathComponent:HQFileName]);

    
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    
}

- (IBAction)butClicked:(UIButton *)sender {
    
    if ([self.loadBut.titleLabel.text isEqualToString:@"开始下载"]) {
       
        [self.task resume];
        
        [self.loadBut setTitle:@"暂停" forState:UIControlStateNormal];
        
    }
    else if([self.loadBut.titleLabel.text isEqualToString:@"暂停"]){
        
        [self.task suspend];
        
        [self.loadBut setTitle:@"继续下载" forState:UIControlStateNormal];
        
    }
    else{
        
       [self.task resume];
       [self.loadBut setTitle:@"暂停" forState:UIControlStateNormal];
        
    }
    
}

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler{
    
    [self.outputStream open];
    
    //必须开启才能接收服务端的请求
    completionHandler(NSURLSessionResponseAllow);
    
    //表示服务器当前能返回给我们的文件等大小
    self.fileTotalSize=[response.allHeaderFields[@"Content-Length"] integerValue]+[self getCurrentDownloadSize];

    //把文件的总大小写入我们的plist文件，key就用我们的文件名
    NSString *plistPath=[HQFilePath stringByAppendingPathComponent:@"fileSize.plist"];
    
    NSMutableDictionary *dict=[NSMutableDictionary dictionaryWithContentsOfFile:plistPath];
    if (dict==nil) {
        dict=[NSMutableDictionary dictionary];
    }
    //用我们的md5的url当作key
    dict[HQFileName]=@(self.fileTotalSize);
    
    [dict writeToFile:plistPath atomically:YES];
    
    
}

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data{
    
    
    [self.outputStream write:[data bytes] maxLength:data.length];
    
    self.fileCurrentSize=[self getCurrentDownloadSize];
    
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        
        self.downSize.hidden=NO;
        
        self.pro.progress=(1.0*self.fileCurrentSize/self.fileTotalSize);
        
        self.downSize.text=[NSString stringWithFormat:@"%.0f%%",(1.0*self.fileCurrentSize/self.fileTotalSize)*100];
        
    }];

    NSLog(@"%ld",self.fileCurrentSize);
    
}

-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{
    
    if (error) {
        return;
    }
    
    
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
    
        self.downloadStatus.hidden=NO;
        
        self.loadBut.enabled=NO;
        
        [self.loadBut setTitle:@"开始下载" forState:UIControlStateNormal];
    }];
    
    [self.outputStream close];
    self.outputStream=nil;
    
    self.task=nil;
    
}

//判断文件现在已经下载了多少
-(NSInteger) getCurrentDownloadSize{
    
    NSDictionary *dict=[[NSFileManager defaultManager] attributesOfItemAtPath:[HQFilePath stringByAppendingPathComponent:HQFileName] error:nil];
    
    return [dict[@"NSFileSize"] integerValue];
    
}


@end