【待整理】IOS开发之下载

一、传统的下载文件的方式　　

- (void)downloaderWithUrl:(NSURL *)url
{
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {

        if (!connectionError)
        {
            NSHTTPURLResponse *urlResponse = (NSHTTPURLResponse *)response;
            if (urlResponse.statusCode == 200 || urlResponse.statusCode == 304)
            {
                [data writeToFile:@"/Users/gxiangzi/Desktop/a.mp4" atomically:YES];
                NSLog(@"OK");
            }
        }else
        {
            NSLog(@"错误");
        }
    }];
}

但是这种方式存在着弊端:

　　1> 用不无法跟踪下载的进度，无法直观的显示下载进度

　　2> 文件下载的时候，都会先下载到内存之中，导致内存 > 所需文件的大小长度，会造成程序崩溃等现象(可以查看内存的耗费)

二、代理的方式下载程序(NSURLConnectionDownloadDelegate)

#import "GXDownloader.h"

@interface GXDownloader () <NSURLConnectionDownloadDelegate>

@end

@implementation GXDownloader

- (void)downloaderWithUrl:(NSURL*)url
{
    NSURLRequest* request = [NSURLRequest requestWithURL:url];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

#pragma mark - NSURLConnectionDownloadDelegate

/**
 bytesWritten: 表示下载的数据字节数
 totalBytesWritten:总的已经下载的字节数
 expectedTotalBytes:期望的总的字节数
 */
- (void)connection:(NSURLConnection*)connection didWriteData:(long long)bytesWritten totalBytesWritten:(long long)totalBytesWritten expectedTotalBytes:(long long)expectedTotalBytes
{
    float progress = (float)totalBytesWritten / expectedTotalBytes;
    NSLog(@"%f", progress);
}

/**
 *  @param connection
 *  @param totalBytesWritten : 总的已经下载的字节数
 *  @param expectedTotalBytes : 期望总的字节数
 */
- (void)connectionDidResumeDownloading:(NSURLConnection*)connection totalBytesWritten:(long long)totalBytesWritten expectedTotalBytes:(long long)expectedTotalBytes
{
}

/**
 *  @param connection
 *  @param destinationURL:下载完的目标路径
 */
- (void)connectionDidFinishDownloading:(NSURLConnection*)connection destinationURL:(NSURL*)destinationURL
{
    NSLog(@"%@", destinationURL);
}

优点：

　　1> 该种方式可以跟踪文件下载的进度；

　　2> 也可以解决内存消耗过大的问题

弊端：  这丫的 下载的文件没有 ，就是虽然你显示下载完成，但是你本地找不到该文件------没有任何卵用

三、第三种方式--代理(NSURLConnectionDataDelegate)

//
//  GXDownloader.m
//  02-下载
//
//  Created by gxiangzi on 15/8/21.
//  Copyright (c) 2015年 hqu. All rights reserved.
//

#import "GXDownloader.h"

@interface GXDownloader () <NSURLConnectionDataDelegate>

// 文件的总长度
@property (nonatomic, assign) long long expectedContentLength;

// 已经接受到文件的长度
@property (nonatomic, assign) long long receivedContentLength;

// 已经接收到的文件的总长度
@property (nonatomic, strong) NSMutableData* receivedData;

@end

@implementation GXDownloader

- (void)downloaderWithUrl:(NSURL*)url
{
    NSURLRequest* request = [NSURLRequest requestWithURL:url];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

#pragma mark - NSURLConnectionDataDelegate

/**
 *  已经接受到响应头
 */
- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
{
    self.expectedContentLength = response.expectedContentLength;
}

/**
 *  文件接受到一点的时候就是用
 */
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    // 把二进制数据进行拼接
    [self.receivedData appendData:data];
    // 拼接长度
    self.receivedContentLength += data.length;

    float progress = (float)self.receivedContentLength / self.expectedContentLength;

    NSLog(@"下载进度: %.2f",progress);

}

/**
 *  下载出错的时候调用
 */
- (void)connection:(NSURLConnection*)connection didFailWithError:(NSError*)error
{
}

/**
 *  当下载完成的时候调用
 */
- (void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"下载完成");

    // IOS 的文件路径，只能讲软件操作的数据放在沙盒内
    NSString *path = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
    NSString *fileName = [path stringByAppendingPathComponent:@"love.mp4"];

    NSLog(@"%@",fileName);

    [self.receivedData writeToFile:fileName atomically:YES];

}

#pragma mark -懒加载
- (NSMutableData*)receivedData
{
    if (!_receivedData) {
        _receivedData = [NSMutableData data];
    }
    return _receivedData;
}

@end

优点:

　　1> 可以检测到进度的问题

　　2> 文件的写入的路径之中，文件可以存在

弊端：

　　占用的内存太大　　

为了解决上面的问题： 引入了NSHandle  和 NSOutputStream ------下一点 写入文件一点

四、NSHandle的使用

//
//  GXDownloader.m
//  02-下载
//
//  Created by gxiangzi on 15/8/21.
//  Copyright (c) 2015年 hqu. All rights reserved.
//

#import "GXDownloader.h"

@interface GXDownloader () <NSURLConnectionDataDelegate>

// 文件的总长度
@property (nonatomic, assign) long long expectedContentLength;

// 已经接受到文件的长度
@property (nonatomic, assign) long long receivedContentLength;

@end

@implementation GXDownloader

- (void)downloaderWithUrl:(NSURL*)url
{
    NSURLRequest* request = [NSURLRequest requestWithURL:url];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

#pragma mark - NSURLConnectionDataDelegate

/**
 *  已经接受到响应头
 */
- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
{
    self.expectedContentLength = response.expectedContentLength;
}

/**
 *  文件接受到一点的时候就是用
 */
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    // 拼接长度
    self.receivedContentLength += data.length;

    float progress = (float)self.receivedContentLength / self.expectedContentLength;
    NSLog(@"%f",progress);

    NSString* path = @"/Users/gxiangzi/Desktop/a.mp4";

    NSFileHandle* handle = [NSFileHandle fileHandleForWritingAtPath:path];
    // 如果handle  不会帮我们创建文件
    if (handle == nil) {
        [data writeToFile:path atomically:YES];
    }
    else {
        //让offset指向文件的末尾,在末尾处追加数据
        [handle seekToEndOfFile];
        //写输入
        [handle writeData:data];
        //关闭  (等文件下载完成关闭更好)
        [handle closeFile];
    }

}

/**
 *  当下载完成的时候调用
 */
- (void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"下载完成");
}

@end

原理：下载一点数据 写一点数据

效果:能够达到占用很少内存

五、NSOutputStream的使用

//
//  GXDownloader.m
//  02-下载
//
//  Created by gxiangzi on 15/8/21.
//  Copyright (c) 2015年 hqu. All rights reserved.
//

#import "GXDownloader.h"

@interface GXDownloader () <NSURLConnectionDataDelegate>

// 文件的总长度
@property (nonatomic, assign) long long expectedContentLength;

// 已经接受到文件的长度
@property (nonatomic, assign) long long receivedContentLength;

@property (nonatomic, strong) NSOutputStream* stream;

@end

@implementation GXDownloader

- (void)downloaderWithUrl:(NSURL*)url
{
    NSURLRequest* request = [NSURLRequest requestWithURL:url];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

#pragma mark - NSURLConnectionDataDelegate

/**
 *  已经接受到响应头
 */
- (void)connection:(NSURLConnection*)connection didReceiveResponse:(NSURLResponse*)response
{
    self.expectedContentLength = response.expectedContentLength;

    NSString* path = @"/Users/gxiangzi/Desktop/a.mp4";

    // 注意 此处的url 为本地的路径
    // 前面加 file:// 无效
    // 只能使用 [NSURL fileURLWithPath:path]
   self.stream = [NSOutputStream outputStreamWithURL:[NSURL fileURLWithPath:path] append:YES];

    [self.stream open];

}

/**
 *  文件接受到一点的时候就是用
 */
- (void)connection:(NSURLConnection*)connection didReceiveData:(NSData*)data
{
    // 拼接长度
    self.receivedContentLength += data.length;

    float progress = (float)self.receivedContentLength / self.expectedContentLength;
    NSLog(@"%f", progress);

    [self.stream write:data.bytes maxLength:data.length];
}

/**
 *  当下载完成的时候调用
 */
- (void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"下载完成");
    [self.stream close];
}

- (NSOutputStream *)stream
{
    if (_stream == nil)
    {
        _stream = [[NSOutputStream alloc] init];
    }
    return _stream;
}

@end