Objective-C 中的 Url 加载系统

URL 加载在访问 URL（即来自 internet 的项目）时很有用。它使用了以下类：

NSMutableURLRequest
NSURLConnection
NSURLCache
NSURLAuthenticationChallenge
NSURLCredential
NSURLProtectionSpace
NSURLResponse
NSURLDownload
NSURLSession

下面是一个简单的 url 加载实例。这不能在命令行上运行。我们需要创建 Cocoa 应用程序。

这可以通过在 XCode 中选择 New，然后在出现的窗口的 OSX 应用程序部分下投影并选择 Cocoa 应用程序来完成。

单击 "下一步" 完成一系列步骤，系统将要求您提供项目名称，您可以为其命名。

appdelegate.h 文件如下:

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

更新 AppDelegate.m 文件如下:

#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

结果如下:

2022-07-07 16:50:31.953 NSURLConnectionSample[1444:303] {
   "time": "11:20:31 AM",
   "milliseconds_since_epoch": 1380453631948,
   "date": "07-07-2022"
}

在上面的程序中，我们创建了一个简单的 URL 连接，它以 JSON 格式占用时间并显示时间。

Objective-C 中的 Url 加载系统

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