1、使用AFNetwoking

//導入
#import "AFNetworking.h"
#import "UIKit+AFNetworking.h"
//和導入系統框架  MobileCoreServices、SystemConfiguration、sec 。。忽略

網絡監聽

AFNetworkReachabilityManager  網絡監聽管理者對象

方法：
設置監聽
  setReachabilityStatusChangeBlock 
啟動監聽
  startMonitoring 

代碼：

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event{ 
//創建網絡監聽管理者對象 AFNetworkReachabilityManager *manager = [AFNetworkReachabilityManager sharedManager]; 
/* typedef NS_ENUM(NSInteger, AFNetworkReachabilityStatus) { 
  AFNetworkReachabilityStatusUnknown = -1,//未識別的網絡 
  AFNetworkReachabilityStatusNotReachable = 0,//不可達的網絡(未連接) 
  AFNetworkReachabilityStatusReachableViaWWAN = 1,//2G,3G,4G... 
  AFNetworkReachabilityStatusReachableViaWiFi = 2,//wifi網絡 }; */ 
//設置監聽 
 [manager setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) { 
  switch (status) { 
    case AFNetworkReachabilityStatusUnknown: 
      NSLog(@"未識別的網絡"); 
      break; 
    case AFNetworkReachabilityStatusNotReachable:
      NSLog(@"不可達的網絡(未連接)"); 
      break; 
    case AFNetworkReachabilityStatusReachableViaWWAN: 
      NSLog(@"2G,3G,4G...的網絡"); 
      break; 
    case AFNetworkReachabilityStatusReachableViaWiFi: 
      NSLog(@"wifi的網絡"); 
      break; 
    default: 
      break; 
    } 
  }]; 
//開始監聽 
[manager startMonitoring];}

下載

//
NSURLSessionConfiguration
> + defaultSessionConfiguration 
：創建一個默認的NSURLSessionConfiguration

AFURLSessionManager
> - initWithSessionConfiguration 
：初始化AFURLSessionManager 通過 NSURLSessionConfiguration

> - downloadTaskWithRequest
：創建 NSURLSessionDownloadTask 對象

NSURLSessionDownloadTask
> - resume 

代碼：

    NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    //繼承自AFURLSessionManager。類似于1和2的關系。也是方便HTTP以及https請求的使用，增加了一些接口，方便調用。
    AFURLSessionManager *sessionManager = [[AFURLSessionManager alloc] initWithSessionConfiguration:sessionConfig];
    
    NSURL *url = [NSURL URLWithString:@"http://www.361810.com/uploads/allimg/150409/2053363O4-0.jpg"];
    
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    //progress 進度條 destination 最終地址  completionHandler 完成處理程序
    NSURLSessionDownloadTask *downloadTask = [sessionManager downloadTaskWithRequest:request progress:nil destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {
        
        
        
        NSLog(@"%@",[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject]);
        
        //創建下載地址
        NSURL *downloadURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
        return [downloadURL URLByAppendingPathComponent:[response suggestedFilename]];
        
    } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {
        
        //這時候已經在主線程了
        
        //先將filePath轉換成data類型
        NSData *data = [NSData dataWithContentsOfURL:filePath];
        //轉換成image
        UIImage *image = [UIImage imageWithData:data];
        _imageView.image = image;
    }];
    
    //繼續操作
    [downloadTask resume];

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