iOS开发系列-文件下载

小文件下载

NSURLConnection下载小文件

#import "ViewController.h"

@interface ViewController ()<NSURLConnectionDataDelegate>
/** 记录文件的总大小 */
@property (nonatomic, assign) long long totalSize;
/** 下载的文件名  */
@property (nonatomic, strong) NSString *fileName;
/** 已经下载的data */
@property (nonatomic, strong) NSMutableData *downLoadData;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/resources/videos/minion_04.mp4"];
    NSURLRequest *rquest = [NSURLRequest requestWithURL:url];
    // 发送请求
    [NSURLConnection connectionWithRequest:rquest delegate:self];
    
}

#pragma mark - NSURLConnectionDataDelegate
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSHTTPURLResponse *httpRespone = (NSHTTPURLResponse *)response;
    _totalSize = httpRespone.expectedContentLength; // 获取下载文件的总大小
    _fileName = httpRespone.suggestedFilename; // 下载文件的名
    NSLog(@"%@", httpRespone);
    // 获取响应头字段的value
    // NSString *contentLength = httpRespone.allHeaderFields[@"Content-Length"]; // 也可以获取文件的总长度
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // 拼接NSData
    [self.downLoadData appendData:data];
    
    // 计算进度
    NSUInteger currLength = self.downLoadData.length;
    double progress = (currLength * 1.0 / self.totalSize) * 100;
    NSLog(@"------------------%@", [NSString stringWithFormat:@"%.2f%%", progress]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    // 下载完成将下载的Data写入沙河
    NSString *path = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject;
    NSString *filePath = [path stringByAppendingPathComponent:self.fileName];
    [self.downLoadData writeToFile:filePath options:kNilOptions error:nil];
    
}

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

@end

NSURLSession下载小文件

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSURL *url = [NSURL URLWithString:@"http://img.zcool.cn/community/0142135541fe180000019ae9b8cf86.jpg@1280w_1l_2o_100sh.png"];
    // 创建session
    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDownloadTask *task = [session downloadTaskWithURL:url completionHandler:^(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        NSString *filePath = [FMFILE stringByAppendingPathComponent:response.suggestedFilename];
        [[NSFileManager defaultManager] moveItemAtURL:location toURL:[NSURL fileURLWithPath:filePath] error:nil];
    }];
    
    // 执行task
    [task resume];
  
}

NSURLSessionDownloadTask下载完文件后自动将文件临时存储在沙盒的tmp目录下，通过Block的location返回。我们需要将tmp目录下的文件剪切到要存储的目录下否则系统自动清理。
这里注意:[NSURL fileURLWithPath:filePath]返回的URL是带有协议头的，而[NSURL URLWithString:@""];返回的是不带协议头的URL。

因此开发中建议使用NSURLSessionDownloadTask下载小文件。

大文件下载

NSURLConnection下载大文件

大文件的下载不能像小文件下载的方式将服务器每次返回的data拼接到内存。而是需要边下载边写进沙盒，这里需要使用NSFileHander这个类。

#import "ViewController.h"

#define FMFILE NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject

@interface ViewController ()<NSURLConnectionDataDelegate>
/** 记录文件的总大小 */
@property (nonatomic, assign) long long totalLength;
/** 当前总长度 */
@property (nonatomic, assign) long long currLength;

@property (nonatomic, strong) NSFileHandle *handle;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/resources/videos/minion_04.mp4"];
    NSURLRequest *rquest = [NSURLRequest requestWithURL:url];
    // 发送请求
    [NSURLConnection connectionWithRequest:rquest delegate:self];
    
}

#pragma mark - NSURLConnectionDataDelegate
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // 下载完成将下载的Data写入沙河
    NSHTTPURLResponse *httpRespone = (NSHTTPURLResponse *)response;
    NSString *fileName = httpRespone.suggestedFilename; // 下载文件的名
    NSString *filePath = [FMFILE stringByAppendingPathComponent:fileName];
    
    // 接收到一个响应创建空的文件
    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
    
    self.totalLength = httpRespone.expectedContentLength; // 获取下载文件的总大小
    
    self.handle = [NSFileHandle fileHandleForWritingAtPath:filePath];
}

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

    // 每次文件从文件内容尾部拼接
    [self.handle seekToEndOfFile];
    
    // 开始写入数据
    [self.handle writeData:data];
    
    // 拼接总长度
    self.currLength += data.length;
    
    // 计算当前进度
    CGFloat progress = self.currLength * 1.0 / self.totalLength;
    NSLog(@"下载进度----%.2f%%", progress *100);
    
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [self.handle closeFile];
    self.handle = nil;
    
    // 清零数据
    self.currLength = 0;
    self.totalLength = 0;
}

@end

NSURLSession下载大文件

#import "ViewController.h"

#define FMFILE NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).firstObject
@interface ViewController ()<NSURLSessionDownloadDelegate>

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186:32812/resources/videos/minion_04.mp4"];
    
    NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    NSURLSessionDownloadTask *task = [session downloadTaskWithURL:url];
    
    [task resume];
}

#pragma mark - NSURLSessionDataDelegate
/*
 每当写入数据到临时文件就会调用该方法
 bytesWritten 这次写入数据的长度
 totalBytesWritten 已经写入的文件长度
 totalBytesExpectedToWrite 要下载文件的中长度
 */
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    CGFloat progress = totalBytesWritten * 1.0 / totalBytesExpectedToWrite;
    NSLog(@"----------%.2f%%", progress*100);
}

/*
 恢复下载
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes
{
    
}

// 现在完毕
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSString *filePath = [FMFILE stringByAppendingPathComponent:downloadTask.response.suggestedFilename];
    // 剪切文件
    [[NSFileManager defaultManager] moveItemAtURL:location toURL:[NSURL fileURLWithPath:filePath] error:nil];
}

// 完成跟失败都会来到这个代理方法
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    NSLog(@"------------%s", __func__);
}
@end

NSURLSession断点下载大文件

NSURLSession创建的Task的的父类NSURLSessionTask有三个方法，因此它的子类都有这些方法。我们就可以利用这几个方法做断点下载。

- (void)suspend;
- (void)resume;
- (void)cancel;