ios实现断点下载

#import "ZYDownViewController.h"

@interface ZYDownViewController ()

@end

@implementation ZYDownViewController

{

   // NSMutableData * buffer;

    long long  _totalLength; //文件总大小

    long long  _currentLength; //当前下载大小  默认为0

    NSFileHandle * fileHandle;

    NSURLConnection * conn;

}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil

{

    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];

    if (self) {

        // Custom initialization

    }

    return self;

}

- (void)viewDidLoad

{

    [super viewDidLoad];

    // Do any additional setup after loading the view from its nib.

    NSString * pp=[self getPath];

    fileHandle =[NSFileHandle fileHandleForWritingAtPath:pp];

    _progress.progressViewStyle=1;

}

- (void)didReceiveMemoryWarning

{

    [super didReceiveMemoryWarning];

    // Dispose of any resources that can be recreated.

}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{

    //buffer=[[NSMutableData alloc] init];

    _totalLength=[response expectedContentLength] + _currentLength;

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{

    //[buffer appendData:data];

    if (fileHandle) {

        //定位到要写入文件的地方

        [fileHandle seekToFileOffset:[fileHandle seekToEndOfFile]];

        [fileHandle writeData:data];

    }

    _currentLength+=data.length;

    float f=(float)_currentLength/(float)_totalLength;

    _progress.progress=f;

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection{

    UIAlertView * alert=[[UIAlertView alloc]  initWithTitle:@"温馨提示" message:@"下载成功" delegate:self cancelButtonTitle:@"返回"  otherButtonTitles:nil, nil];

    [alert show];

}

- (IBAction)DownBtnClick:(id)sender {

    //断点下载

    NSString * path=[self getPath];   //获取路径

    long long filesize=0;

    NSFileManager * fileMg=[NSFileManager defaultManager];

    //获取文件信息字典

    NSDictionary  *dic=[fileMg  attributesOfItemAtPath:path error:nil];

    // 获取文件大小

    NSNumber * contentLength=[dic objectForKey:NSFileSize];

    //获取已经下载多少

    filesize=[contentLength longLongValue];

    _currentLength=filesize;

    //获取下载文件的大小

    NSURL * url=[NSURL URLWithString:@"http://localhost:8080/Servelet/3333.dmg"]; //测试服务代码

    NSMutableURLRequest * request=[NSMutableURLRequest requestWithURL:url];

    [request setHTTPMethod:@"POST"];

    //设置请求过后的字节  因为我们要求都是在建立在已经获取文件的大小的基础上的进行的

    [request addValue:[NSString stringWithFormat:@"bytes=%qu-",_currentLength] forHTTPHeaderField:@"Range"];

    conn=[NSURLConnection connectionWithRequest:request delegate:self];

}

-(NSString *) getPath{

    NSString * filePath=[NSHomeDirectory() stringByAppendingPathComponent:@"Documents/test.dmg"];

    NSFileManager * fileMg=[NSFileManager defaultManager];

    if (![fileMg fileExistsAtPath:filePath]) {

        [fileMg createFileAtPath:filePath contents:nil attributes:nil];

    }

    return filePath;

}

- (IBAction)CancelBtnClick:(id)sender {

    [conn cancel];

}

@end