iOS 学习 - 10下载(1) NSURLConnection 篇

程序的实现需要借助几个对象：

NSURLRequest：建立了一个请求，可以指定缓存策略、超时时间。和NSURLRequest对应的还有一个NSMutableURLRequest，如果请求定义为NSMutableURLRequest则可以指定请求方法（GET或POST）等信息。

NSURLConnection：用于发送请求，可以指定请求和代理。当前调用NSURLConnection的start方法后开始发送异步请求。

当然了这种方法比较原始。。。

//
//  ViewController.m
//  xiazai
//
//  Copyright © 2016年 asamu. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()<NSURLConnectionDataDelegate>
{
    NSMutableData *_data;//响应数据
    UITextField *_textField;
    UIButton *_button;
    UIProgressView *_progressView;
    UILabel *_label;
    long long _totalLength;
    NSDictionary *_musicDic;
}
@end

@implementation ViewController
#pragma mark -- UI方法
- (void)viewDidLoad {
    [super viewDidLoad];
    [self analysisJson];
    [self layoutUI];

}
#pragma mark -- 私有方法
#pragma mark  解析 JSON
-(void)analysisJson{
    NSError *error;
    NSString *str = @"http://douban.fm/j/mine/playlist?channel=3";
    NSURL *url = [NSURL URLWithString:str];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
    NSDictionary *musicDic = [[NSDictionary alloc]init];
    //遍历字典 取出 key - @"song"
    for (musicDic in dic[@"song"]) {
        _musicDic = musicDic;
    }
}

#pragma mark 界面布局
-(void)layoutUI{
    //地址栏
    _textField = [[UITextField alloc]initWithFrame:CGRectMake(, , , )];
    //加圆角和边框
    _textField.layer.cornerRadius = 3.0f;
    _textField.layer.borderWidth = 0.5f;
    _textField.textColor = [UIColor redColor];
     /*
     解析的 JOSN 中的 歌曲名加上 .mp3 的后缀
     这个名字就是存储在沙盒中的名字，所以要加 .mp3
     由于名称不一样，所以不会覆盖
     */
    NSString *musicName = [_musicDic[@"title"] stringByAppendingString:@".mp3"];
    _textField.text = musicName;
    [_textField sizeToFit];
    [self.view addSubview:_textField];
    //进度条
    _progressView = [[UIProgressView alloc]initWithFrame:CGRectMake(, , , )];
    [self.view addSubview:_progressView];
    //状态显示
    _label = [[UILabel alloc]initWithFrame:CGRectMake(, , , )];
    _label.textColor = [UIColor colorWithRed: green:/255.0 blue:1.0 alpha:1.0];
    [self.view addSubview:_label];
    //下载按钮
    _button = [[UIButton alloc]initWithFrame:CGRectMake(, , , )];
    [_button setTitle:@"下载" forState:UIControlStateNormal];
    [_button setTitleColor:[UIColor colorWithRed: green:/255.0 blue:1.0 alpha:1.0] forState:UIControlStateNormal];
    [_button addTarget:self action:@selector(sendRequest) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:_button];
}
#pragma mark -- 更新进度
-(void)updateProgress{
    if (_data.length == _totalLength) {
        _label.text = @"Finish downloaded";
    }else{
        _label.text = @"downing...";
        [_progressView setProgress:(float)_data.length/_totalLength];
    }
}
#pragma mark -- 发送请求
-(void)sendRequest{
    NSLog(@"begin");
    NSString *urlStr = [NSString stringWithFormat:_musicDic[@"url"],_textField.text];
    //解码
    urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    // 创建 URL 链接
    NSURL *url = [NSURL URLWithString:urlStr];
    //创建请求
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:20.0f];
    //创建连接
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    //启动连接
    [connection start];
}
#pragma mark -- 连接代理方法
#pragma mark 开始响应
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"receive response");
    _data = [[NSMutableData alloc]init];
    _progressView.progress = ;
    //通过响应头中的 Content-Length 取得整个响应的长度
    NSHTTPURLResponse *httpRespose = (NSHTTPURLResponse *)response;
    NSDictionary *httpResponseHeaderFields = [httpRespose allHeaderFields];
    _totalLength = [[httpResponseHeaderFields objectForKey:@"Content-Length"]longLongValue];
}
#pragma mark 接收响应数据,(根据响应内容的大小此方法会被重复调用)
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    NSLog(@"Receive data");
    //连续接收数据
    [_data appendData:data];
    //更新进度
    [self updateProgress];
}
#pragma mark 接收数据完成
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"loading finish");
    //数据接收完保存文集(注意苹果官方要求:下载数据只能保存在缓存目录)
    NSString *savePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
    savePath = [savePath stringByAppendingPathComponent:_textField.text];
    [_data writeToFile:savePath atomically:YES];
    NSLog(@"path:%@",savePath);
}
#pragma mark 请求失败
-(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
    NSLog(@"connection error,error detail is:%@",error.localizedDescription);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

随笔 10（）部分，都来自 KenshinCui,后系列就不一一列出，估计大神的 url 没用了，所以我换了个音乐的 url，可以用。初学者，若有错误，敬请指出，不甚感激。