网络请求AFNetworking使用量不用过多的说了，但是在开发过程中，需要用到自己去封装一个网络请求，此处主要是说一下NSUrlSession的用法，顺便说一下，这个网络请求库，是同时支持HTTP和HTTPS请求的，应为在iOS9之后，默认的请求方式是HTTPS；

当然，Xcode工程中需要在info.plist文件中加入下面的节点：App Transport Security Settings(字典类型) ->添加Allow Arbitrary Loads为bool类型，设置为YES，大概意思就是说，是否允许任性的加载？ 设为 YES 的话就将禁用了 AppTransportSecurity 转而使用用户自定义的设置。

首先创建一个继承与NSObject的.h和.m的类，.h中的代码如下：

#import <Foundation/Foundation.h>

typedef void (^CompletioBlock)(NSDictionary *dic, NSURLResponse *response, NSError *error);
typedef void (^SuccessBlock)(NSDictionary *data);
typedef void (^FailureBlock)(NSError *error);
@interface SYNetworkHelper : NSObject<NSURLSessionDelegate>

/**
 *  get请求
 */
+ (void)getWithUrlString:(NSString *)url parameters:(id)parameters success:(SuccessBlock)successBlock failure:(FailureBlock)failureBlock;

/**
 * post请求
 */
+ (void)postWithUrlString:(NSString *)url parameters:(id)parameters success:(SuccessBlock)successBlock failure:(FailureBlock)failureBlock;

@end

.m中的实现如下：

#import "SYNetworkHelper.h"

//定义一个变量
static SYFlashNetworkHelper *helper = nil;

@implementation SYNetworkHelper

//实例化对象
+ (instancetype)shareHelper
{
    @synchronized(self) {
        if (!helper) {
            helper = [[SYFlashNetworkHelper alloc] init];
        }
        return helper;
    }
}

//get请求
+ (void)getWithUrlString:(NSString *)url parameters:(id)parameters success:(SuccessBlock)successBlock failure:(FailureBlock)failureBlock
{
    [self shareHelper];
    NSMutableString *mutableUrl = [[NSMutableString alloc] initWithString:url];
    if ([parameters allKeys]) {
        [mutableUrl appendString:@"?"];
        for (id key in parameters) {
            NSString *value = [[parameters objectForKey:key] stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
            [mutableUrl appendString:[NSString stringWithFormat:@"%@=%@&", key, value]];
        }
    }
    NSString *urlEnCode = [[mutableUrl substringToIndex:mutableUrl.length - 1] stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlEnCode]];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:helper delegateQueue:queue];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (error) {
            failureBlock(error);
        } else {
            NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
            successBlock(dic);
        }
    }];
    [dataTask resume];
}

//post请求
+ (void)postWithUrlString:(NSString *)url parameters:(id)parameters success:(SuccessBlock)successBlock failure:(FailureBlock)failureBlock
{
    [self shareHelper];
    NSURL *nsurl = [NSURL URLWithString:url];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:nsurl];
    //设置请求方式
    request.HTTPMethod = @"POST"; 
    NSString *postStr = [SYFlashNetworkHelper parseParams:parameters];
    //设置请求体
    request.HTTPBody = [postStr dataUsingEncoding:NSUTF8StringEncoding];
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:helper delegateQueue:queue];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (error) {
            failureBlock(error);
        } else {
            NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
            successBlock(dic);
        }
    }];
    [dataTask resume];
}

//把NSDictionary解析成post格式的NSString字符串
+ (NSString *)parseParams:(NSDictionary *)params
{
    NSString *keyValueFormat;
    NSMutableString *result = [NSMutableString new];
    NSMutableArray *array = [NSMutableArray new];
    //实例化一个key枚举器用来存放dictionary的key
    NSEnumerator *keyEnum = [params keyEnumerator];
    id key;
    while (key = [keyEnum nextObject]) {
        keyValueFormat = [NSString stringWithFormat:@"%@=%@&", key, [params valueForKey:key]];
        [result appendString:keyValueFormat];
        [array addObject:keyValueFormat];
    }
    return result;
}

#pragma mark - NSURLSessionDelegate 代理方法

//主要就是处理HTTPS请求的
- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential *))completionHandler
{
    NSURLProtectionSpace *protectionSpace = challenge.protectionSpace;
    if ([protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        SecTrustRef serverTrust = protectionSpace.serverTrust;
        completionHandler(NSURLSessionAuthChallengeUseCredential, [NSURLCredential credentialForTrust:serverTrust]);
    } else {
        completionHandler(NSURLSessionAuthChallengePerformDefaultHandling, nil);
    }
}

@end