Objective-C URL加載系統

要訪問互聯網的URL，即項目是有用的URL加載。它提供的下面的類的幫助：

NSMutableURLRequest
NSURLConnection
NSURLCache
NSURLAuthenticationChallenge
NSURLCredential
NSURLProtectionSpace
NSURLResponse
NSURLDownload
NSURLSession

下面是一個簡單的URL加載的例子。這是不能在命令行中運行。我們需要創建Cocoa應用程序。

這可以通過選擇新，然後在XCode項目下的OS X應用程序部分出現的窗口中選擇Cocoa應用程序。

完成步驟的順序點擊下一步，會被要求提供一個項目名稱，給它一個名字。

appdelegate.h 文件內容如下：

#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

現在，當我們編譯並運行程序，我們會得到以下的結果。

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，我們已經創建了一個簡單的JSON格式的，帶有時間和顯示時間的URL連接。

Objective-C教程