网络篇----NSURLConnection断点下载

#import "HMViewController.h"
#import "DACircularProgressView.h"

@interface HMViewController () <NSURLConnectionDataDelegate>
- (IBAction)download:(UIButton *)sender;

/**
*  用来写数据的文件句柄对象
*/
@property (nonatomic, strong) NSFileHandle *writeHandle;
/**
*  文件的总大小
*/
@property (nonatomic, assign) long long totalLength;
/**
*  当前已经写入的文件大小
*/
@property (nonatomic, assign) long long currentLength;

/**
*  连接对象
*/
@property (nonatomic, strong) NSURLConnection *conn;

@property (nonatomic, weak) DACircularProgressView *circleView;
@end

@implementation HMViewController

- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

DACircularProgressView *circleView = [[DACircularProgressView alloc] init];
circleView.frame = CGRectMake(100, 50, 100, 100);
circleView.progressTintColor = [UIColor redColor];
circleView.trackTintColor = [UIColor blueColor];
circleView.progress = 0.0000001;
[self.view addSubview:circleView];
self.circleView = circleView;
}

#pragma mark - NSURLConnectionDataDelegate代理方法
/**
*  请求失败时调用（请求超时、网络异常）
*
*  @param error      错误原因
*/
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
NSLog(@"didFailWithError");
}

/**
*  1.接收到服务器的响应就会调用
*
*  @param response   响应
*/
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
if (self.currentLength) return;

// 文件路径
NSString *caches = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
NSString *filepath = [caches stringByAppendingPathComponent:@"videos.zip"];

// 创建一个空的文件 到 沙盒中
NSFileManager *mgr = [NSFileManager defaultManager];
[mgr createFileAtPath:filepath contents:nil attributes:nil];

// 创建一个用来写数据的文件句柄
self.writeHandle = [NSFileHandle fileHandleForWritingAtPath:filepath];

// 获得文件的总大小
self.totalLength = response.expectedContentLength;
}

/**
*  2.当接收到服务器返回的实体数据时调用（具体内容，这个方法可能会被调用多次）
*
*  @param data       这次返回的数据
*/
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// 移动到文件的最后面
[self.writeHandle seekToEndOfFile];

// 将数据写入沙盒
[self.writeHandle writeData:data];

// 累计文件的长度
self.currentLength += data.length;
//显示下载的百分比
self.circleView.progress = (double)self.currentLength/ self.totalLength;
}

/**
*  3.加载完毕后调用（服务器的数据已经完全返回后）
*/
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
self.currentLength = 0;
self.totalLength = 0;

// 关闭文件
[self.writeHandle closeFile];
self.writeHandle = nil;
}

- (IBAction)download:(UIButton *)sender {
// 状态取反
sender.selected = !sender.isSelected;

// 断点续传
// 断点下载

if (sender.selected) { // 继续（开始）下载
// 1.URL
NSURL *url = [NSURL URLWithString:@"http://localhost:8080/MJServer/resources/videos.zip"];

// 2.请求
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];

// 设置请求头
NSString *range = [NSString stringWithFormat:@"bytes=%lld-", self.currentLength];
[request setValue:range forHTTPHeaderField:@"Range"];

// 3.下载(创建完conn对象后，会自动发起一个异步请求)
self.conn = [NSURLConnection connectionWithRequest:request delegate:self];
} else { // 暂停
[self.conn cancel];
self.conn = nil;
}
}
@end