iOS學習-10下載(1) NSURLConnection 篇

程式的實現需要藉助幾個對象：

NSURLRequest：建立了一個請求，可以指定緩存策略、超時時間。和NSURLRequest對應的還有一個NSMutableURLRequest，如果請求定義為NSMutableURLRequest則可以指定請求方法（GET或POST）等信息。

NSURLConnection：用於發送請求，可以指定請求和代理。當前調用NSURLConnection的start方法後開始發送非同步請求。

當然了這種方法比較原始。。。

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

#import "ViewController.h"

@interface ViewController ()<NSURLConnectionDataDelegate>
{
    NSMutableData *_data;//響應數據
    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];
    //遍歷字典 取出 key - @"song"
    for (musicDic in dic[@"song"]) {
        _musicDic = musicDic;
    }
}

#pragma mark 界面佈局
-(void)layoutUI{
    //地址欄
    _textField = [[UITextField alloc]initWithFrame:CGRectMake(10, 50, 300, 25)];
    //加圓角和邊框
    _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 的尾碼
     這個名字就是存儲在沙盒中的名字，所以要加 .mp3
     由於名稱不一樣，所以不會覆蓋
     */
    NSString *musicName = [_musicDic[@"title"] stringByAppendingString:@".mp3"];
    _textField.text = musicName;
    [_textField sizeToFit];
    [self.view addSubview:_textField];
    //進度條
    _progressView = [[UIProgressView alloc]initWithFrame:CGRectMake(10, 100, 300, 25)];
    [self.view addSubview:_progressView];
    //狀態顯示
    _label = [[UILabel alloc]initWithFrame:CGRectMake(10, 130, 300, 25)];
    _label.textColor = [UIColor colorWithRed:0 green:146/255.0 blue:1.0 alpha:1.0];
    [self.view addSubview:_label];
    //下載按鈕
    _button = [[UIButton alloc]initWithFrame:CGRectMake(10, 500, 300, 25)];
    [_button setTitle:@"下載" forState:UIControlStateNormal];
    [_button setTitleColor:[UIColor colorWithRed:0 green:146/255.0 blue:1.0 alpha:1.0] forState:UIControlStateNormal];
    [_button addTarget:self action:@selector(sendRequest) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:_button];
}
#pragma mark -- 更新進度
-(void)updateProgress{
    if (_data.length == _totalLength) {
        _label.text = @"Finish downloaded";
    }else{
        _label.text = @"downing...";
        [_progressView setProgress:(float)_data.length/_totalLength];
    }
}
#pragma mark -- 發送請求
-(void)sendRequest{
    NSLog(@"begin");
    NSString *urlStr = [NSString stringWithFormat:_musicDic[@"url"],_textField.text];
    //解碼
    urlStr = [urlStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    // 創建 URL 鏈接
    NSURL *url = [NSURL URLWithString:urlStr];
    //創建請求
    NSURLRequest *request = [[NSURLRequest alloc]initWithURL:url cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:20.0f];
    //創建連接
    NSURLConnection *connection = [[NSURLConnection alloc]initWithRequest:request delegate:self];
    //啟動連接
    [connection start];
}
#pragma mark -- 連接代理方法
#pragma mark 開始響應
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSLog(@"receive response");
    _data = [[NSMutableData alloc]init];
    _progressView.progress = 0;
    //通過響應頭中的 Content-Length 取得整個響應的長度
    NSHTTPURLResponse *httpRespose = (NSHTTPURLResponse *)response;
    NSDictionary *httpResponseHeaderFields = [httpRespose allHeaderFields];
    _totalLength = [[httpResponseHeaderFields objectForKey:@"Content-Length"]longLongValue];
}
#pragma mark 接收響應數據,(根據響應內容的大小此方法會被重覆調用)
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
    NSLog(@"Receive data");
    //連續接收數據
    [_data appendData:data];
    //更新進度
    [self updateProgress];
}
#pragma mark 接收數據完成
-(void)connectionDidFinishLoading:(NSURLConnection *)connection{
    NSLog(@"loading finish");
    //數據接收完保存文集(註意蘋果官方要求:下載數據只能保存在緩存目錄)
    NSString *savePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)lastObject];
    savePath = [savePath stringByAppendingPathComponent:_textField.text];
    [_data writeToFile:savePath atomically:YES];
    NSLog(@"path:%@",savePath);
}
#pragma mark 請求失敗
-(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

參考 KenshinCui,估計大神的 url 沒用了，所以我換了個音樂的 url，可以用。初學者，若有錯誤，敬請指出，不甚感激。