Objective-C URL加载系统

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  URL加载系统

  URL加载对于访问URL（即来自Internet的项目）很有用。它在以下类的帮助下提供-

  • NSMutableURLRequest
  • NSURLConnection
  • NSURLCache
  • NSURLAuthentication挑战
  • NSURLCredential
  • NSURLProtectionSpace
  • NSURLResponse
  • NSURLDownload
  • NSURLSession

  这是一个简单的URL加载示例。这不能在命令行上运行。我们需要创建可可应用程序。这可以通过在XCode中选择“新建”，然后在出现的窗口的“OS X应用程序”部分下选择“Project”并选择“Cocoa Application”来完成。单击下一步完成步骤序列，将要求您提供一个项目名称，然后可以为其命名。appdelegate.h文件将如下所示-

  
  #import <Cocoa/Cocoa.h>
  
  @interface AppDelegate : NSObject <NSApplicationDelegate>
  
  @property (assign) IBOutlet NSWindow *window;
  
  @end
  

  将AppDelegate.m文件更新为以下内容-

  
  #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时，我们将得到以下结果。

  
  2020-08-24 16:50:31.953 NSURLConnectionSample[1444:303] {
     "time": "11:20:31 AM",
     "milliseconds_since_epoch": 1380453631948,
     "date": "09-29-2013"
  }
  

  在上面的程序中，我们创建了一个简单的URL连接，该连接以JSON格式花费时间并显示时间。