自己封装的下载方法

1.MyDownloader.h文件

#import <Foundation/Foundation.h>

//前置声明
@class MyDownloader;
//协议
@protocol MyDownloaderDelegate <NSObject>

//下载失败
- (void)downloader:(MyDownloader *)downloder failWithReeor:(NSError *)error;

//下载成功,并且下载结束
- (void)downloaderFinish:(MyDownloader *)downloader;

@end


//NSURLConnectionDelegate协议用来处理下载是成功还是失败
//NSURLConnectionDataDelegate 用来处理下载成功时的网络返回的数据
@interface MyDownloader : NSObject<NSURLConnectionDelegate,NSURLConnectionDataDelegate>
//下载的方法
-(void)downloadWithUrlString:(NSString *)urlString;

//代理属性:
//MRC:assign  ARC:weak
/*
        基本类型     代理属性    其它对象
 MRC    assign      assign    retain
 ARC    assign      weak      strong
 */
@property (nonatomic,weak)id<MyDownloaderDelegate>delegate;

//获取下载回来的数据(_receiveData)
//readonly 表示只会自动生成的getter方法
@property (nonatomic,strong)NSData *receiveData;
//类型
@property (nonatomic,assign)NSInteger type;

@end

2.MyDownloader.m文件

#import "MyDownloader.h"
@implementation MyDownloader
{
    //下载对象
    NSURLConnection *_conn;
    //储存下来的数据
    NSMutableData *_receiveData;
}

-(instancetype)init
{
    self = [super init];
    if (self) {
        //初始化下载数据的对象
        _receiveData = [NSMutableData data];
    }
    return self;
}

-(void)downloadWithUrlString:(NSString *)urlString
{
    //1.创建NSURL类型的对象
    NSURL *url = [NSURL URLWithString:urlString];
    
    //2.创建NSURLRequest类型的对象
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    
    //3.创建NSURLConnection类型的对象
    _conn = [NSURLConnection connectionWithRequest:request delegate:self];
}

#pragma mark  -  NSURLConnection代理
//下载成功
//准备接受数据
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [_receiveData setLength:0];
}
//接受下载回来的数据
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [_receiveData appendData:data];
}
//下载完成
//程序会自动切换到主线程
-(void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    if (self.delegate) {
        [self.delegate downloaderFinish:self];
    }
}
//下载失败
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    if (self.delegate) {
        [self.delegate downloader:self failWithReeor:error];
    }
}

@end