要访问互联网的URL，即项目是有用的URL加载。它提供的下面的类的帮助：

• NSMutableURLRequest

• NSURLConnection

• NSURLCache

• NSURLAuthenticationChallenge

• NSURLCredential

• NSURLProtectionSpace

• NSURLResponse

• NSURLDownload

• NSURLSession

下面是一个简单的URL加载的例子。这是不能在命令行中运行。我们需要创建Cocoa应用程序。

这可以通过选择新，然后在XCode项目下的OS X应用程序部分出现的窗口中选择Cocoa应用程序。

完成步骤的顺序点击下一步，会被要求提供一个项目名称，给它一个名字。

appdelegate.h 文件内容如下：

#import <Cocoa/Cocoa.h>

@interface AppDelegate : NSObject <NSApplicationDelegate>

@property (assign) IBOutlet NSWindow *window;

@end

更新以下AppDelegate.m文件：

#import "AppDelegate.h"

@interface SampleClass:NSObject<NSURLConnectionDelegate>
{
    NSMutableData *_responseData;
}
- (void)initiateURLConnection;

@end


@implementation SampleClass

- (void)initiateURLConnection
{
    // Create the request.
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://date.jsontest.com"]];
    
    // Create url connection and fire request
    NSURLConnection *conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    [conn start];
}
#pragma mark NSURLConnection Delegate Methods

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
    // A response has been received, this is where we initialize the instance var you created
    // so that we can append data to it in the didReceiveData method
    // Furthermore, this method is called each time there is a redirect so reinitializing it
    // also serves to clear it
    _responseData = [[NSMutableData alloc] init];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
    // Append the new data to the instance variable you declared
    [_responseData appendData:data];
}

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection
                  willCacheResponse:(NSCachedURLResponse*)cachedResponse {
    // Return nil to indicate not necessary to store a cached response for this connection
    return nil;
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    // The request is complete and data has been received
    // You can parse the stuff in your instance variable now
    NSLog(@"%@",[[NSString alloc]initWithData:_responseData encoding:NSUTF8StringEncoding]);
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
    // The request has failed for some reason!
    // Check the error var
}

@end

@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    SampleClass *sampleClass = [[SampleClass alloc]init];
    [sampleClass initiateURLConnection];
    // Insert code here to initialize your application
}
@end

现在，当我们编译并运行程序，我们会得到以下的结果。

2013-09-29 16:50:31.953 NSURLConnectionSample[1444:303] {
   "time": "11:20:31 AM",
   "milliseconds_since_epoch": 1380453631948,
   "date": "09-29-2013"
}

在上述程序中，我们已经创建了一个简单的JSON格式的，带有时间和显示时间的URL连接。