AFN的使用

首先得下载AFNetworking库文件，下载时得首先弄清楚，你将要开发的软件兼容的最低版本是多少。AFNetworking 2.0或者之后的版本需要xcode5.0版本并且只能为IOS6或更高的手机系统上运行，如果开发MAC程序，那么2.0版本只能在MAC OS X 10.8或者更高的版本上运行。

    NSString *str=[NSString stringWithFormat:@"https://alpha-api.app.net/stream/0/posts/stream/global"];

    NSURL *url = [NSURL URLWithString:[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    //    从URL获取json数据

    AFJSONRequestOperation *operation1 = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, NSDictionary* JSON) {

                NSLog(@"获取到的数据为：%@",JSON);

    } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id data) {

        NSLog(@"发生错误！%@",error);

    }];

    [operation1 start];

第二种方法，利用AFHTTPRequestOperation 先获取到字符串形式的数据，然后转换成json格式，将NSString格式的数据转换成json数据，利用IOS5自带的json解析方法：

   NSString *str=[NSString stringWithFormat:@"https://alpha-api.app.net/stream/0/posts/stream/global"];

    NSURL *url = [NSURL URLWithString:[str stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];

   AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];

    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

        NSString *html = operation.responseString;

             NSData* data=[html dataUsingEncoding:NSUTF8StringEncoding];

             id dict=[NSJSONSerialization  JSONObjectWithData:data options:0 error:nil];

        NSLog(@"获取到的数据为：%@",dict);

    }failure:^(AFHTTPRequestOperation *operation, NSError *error) {

        NSLog(@"发生错误！%@",error);

    }];

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];

    [queue addOperation:operation];

如果发生Error Domain=NSURLErrorDomain Code=-1000 "bad URL" UserInfo=0x14defc80 {NSUnderlyingError=0x14deea10 "bad URL", NSLocalizedDescription=bad URL这个错误，请检查URL编码格式。有没有进行stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding

如何通过URL获取图片

异步获取图片，通过队列实现，而且图片会有缓存，在下次请求相同的链接时，系统会自动调用缓存，而不从网上请求数据。

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0.0f, 100.0f, 100.0f, 100.0f)];


    [imageView setImageWithURL:[NSURL URLWithString:@"http://i.imgur.com/r4uwx.jpg"] placeholderImage:[UIImage imageNamed:@"placeholder-avatar"]];


    [self.view addSubview:imageView];

上面的方法是官方提供的，还有一种方法，

NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.scott-sherwood.com/wp-content/uploads/2013/01/scene.png"]];

    AFImageRequestOperation *operation = [AFImageRequestOperation imageRequestOperationWithRequest:request imageProcessingBlock:nil success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {

       self.backgroundImageView.image = image;

    } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {

       NSLog(@"Error %@",error);

    }];

    [operation start];

如果使用第一种URLWithString：  placeholderImage：会有更多的细节处理，其实实现还是通过AFImageRequestOperation处理，可以点击URLWithString：  placeholderImage：方法进去看一下就一目了然了。所以我觉得还是用第一种好。

如何通过URL获取plist文件

通过url获取plist文件的内容，用的很少，这个方法在官方提供的方法里面没有

    NSString *weatherUrl = @"http://www.calinks.com.cn/buick/kls/Buickhousekeeper.plist";

    NSURL *url = [NSURL URLWithString:[weatherUrl stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    [AFPropertyListRequestOperation addAcceptableContentTypes:[NSSet setWithObject:@"text/plain"]];

    AFPropertyListRequestOperation *operation = [AFPropertyListRequestOperation propertyListRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id propertyList) {

        NSLog(@"%@",(NSDictionary *)propertyList);

    }failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id propertyList) {

        NSLog(@"%@",error);

    }];

    [operation start];

如果稍不留神，可能就出现Error Domain=AFNetworkingErrorDomain Code=-1016 "Expected content type {(

    "application/x-plist"

)}, got text/plain" UserInfo=0x16e91ce0 {NSLocalizedRecoverySuggestion=

...

...

, AFNetworkingOperationFailingURLRequestErrorKey= { }, NSErrorFailingURLKey=, NSLocalizedDescription=Expected content type {(

    "application/x-plist"

)}, got text/plain, AFNetworkingOperationFailinponseErrorKey= { URL:  } { status code: 200, headers {

    "Accept-Ranges" = bytes;

    Connection = "keep-alive";

    "Content-Length" = 974;

    "Content-Type" = "text/plain";

    Date = "Sat, 25 Jan 2014 07:29:26 GMT";

    Etag = ""1014c2-3ce-4ee63e1c80e00"";

    "Last-Modified" = "Wed, 25 Dec 2013 23:04:24 GMT";

    Server = "nginx/1.4.2";

} }}

可能还会出现乱码，解决办法就是[AFPropertyListRequestOperation addAcceptableContentTypes:[NSSet setWithObject:@"text/plain"]];

如何通过URL获取XML数据

xml解析使用AFXMLRequestOperation，需要实现苹果自带的NSXMLParserDelegate委托方法，XML中有一些不需要的协议格式内容，所以就不能像json那样解析，还得实现委托。我之前有想过能否所有的XML链接用一个类处理，而且跟服务端做了沟通，结果很不方便，效果不好。XML大多标签不同，格式也不固定，所以就有问题，使用json就要方便的多。

第一步；在.h文件中加入委托NSXMLParserDelegate

第二步；在.m文件方法中加入代码

    NSURL *url = [NSURL URLWithString:@"http://113.106.90.22:5244/sshopinfo"];

    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    AFXMLRequestOperation *operation =

    [AFXMLRequestOperation XMLParserRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, NSXMLParser *XMLParser) {

        XMLParser.delegate = self;

        [XMLParser setShouldProcessNamespaces:YES];

        [XMLParser parse];

    }failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, NSXMLParser *XMLParser) {

        NSLog(@"%@",error);

    }];

    [operation start];

第三步；在.m文件中实现委托方法

    //在文档开始的时候触发

-(void)parserDidStartDocument:(NSXMLParser *)parser{

    NSLog(@"解析开始！");

}

//解析起始标记

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict{

    NSLog(@"标记：%@",elementName);

}

//解析文本节点

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string{

    NSLog(@"值：%@",string);

}

//解析结束标记

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName{

    NSLog(@"结束标记：%@",elementName);

}

//文档结束时触发

-(void) parserDidEndDocument:(NSXMLParser *)parser{

    NSLog(@"解析结束！");

}

运行的结果：

   BaseURLString = @"http://www.raywenderlich.com/downloads/weather_sample/";

    NSURL *baseURL = [NSURL URLWithString:[NSString stringWithFormat:BaseURLString]];

    NSDictionary *parameters = [NSDictionary dictionaryWithObject:@"json" forKey:@"format"];

    AFHTTPClient *client = [[AFHTTPClient alloc] initWithBaseURL:baseURL];

    [client registerHTTPOperationClass:[AFJSONRequestOperation class]];

    [client setDefaultHeader:@"Accept" value:@"text/html"];

    [client postPath:@"weather.php" parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {

        NSString* newStr = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];

        NSLog(@"POST请求:%@",newStr);

    }failure:^(AFHTTPRequestOperation *operation, NSError *error) {

        NSLog(@"%@",error);

    }];

    [client getPath:@"weather.php" parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {

        NSString* newStr = [[NSString alloc] initWithData:responseObject encoding:NSUTF8StringEncoding];

        NSLog(@"GET请求：%@",newStr);

    }failure:^(AFHTTPRequestOperation *operation, NSError *error) {

        NSLog(@"%@",error);

    }];

运行结果：