为什么用于 Web 服务的 RESTful 不适用于 iOS（提供的代码）？

Question

I used the following code to test out fetching data from the provided link in the code, but both data and response are nil.

RestViewController.h

#import <UIKit/UIKit.h>

@interface RestViewController : UIViewController

@property (nonatomic, strong) IBOutlet UILabel *greetingId;
@property (nonatomic, strong) IBOutlet UILabel *greetingContent;

- (IBAction)fetchGreeting;

@end

RestViewController.m

#import "RestViewController.h"

@interface RestViewController ()

@end

@implementation RestViewController

- (IBAction)fetchGreeting;
{
    NSURL *url = [NSURL URLWithString:@"http://rest-service.guides.spring.io/greeting"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [NSURLConnection sendAsynchronousRequest:request
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *response,
                                               NSData *data, NSError *connectionError)
     {
         if (data.length > 0 && connectionError == nil)
         {
             NSDictionary *greeting = [NSJSONSerialization JSONObjectWithData:data
                                                                      options:0
                                                                        error:NULL];
             self.greetingId.text = [[greeting objectForKey:@"id"] stringValue];
             self.greetingContent.text = [greeting objectForKey:@"content"];
         }
     }];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    [self fetchGreeting];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

In the storyboard, there are 3 UI components, two text labels and one button. Once the button (fetchGreeting) is clicked, the labels should fetch the data from the link and update the two text labels (greetingID and greetingContent) with the right data.

I followed the instructions from the following link exactly, but it still doesn't seem to fetch any data and can't seem to figure it out. Any guidance would be greatly appreciated.

Answer 1

Your code has a type here:

- (IBAction)fetchGreeting;

Should be:

- (IBAction)fetchGreeting

Also, you're using a deprecated method for IOS9, which is this:

    [NSURLConnection sendAsynchronousRequest:request
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:^(NSURLResponse *response,
                                           NSData *data, NSError *connectionError)
 {
     if (data.length > 0 && connectionError == nil)
     {
         NSDictionary *greeting = [NSJSONSerialization JSONObjectWithData:data
                                                                  options:0
                                                                    error:NULL];
         self.greetingId.text = [[greeting objectForKey:@"id"] stringValue];
         self.greetingContent.text = [greeting objectForKey:@"content"];
     }
 }];

Also, if you're planning to work with IOS9, you need to either use HTTPS or temporarily allow HTTP connections by adding this to your project's PLIST.

    <key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key><true/>
</dict>

Here's an updated method:

    NSURLSessionDataTask *downloadTask = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    if (data.length > 0 && error == nil)
    {
        NSDictionary *greeting = [NSJSONSerialization JSONObjectWithData:data
                                                                 options:0
                                                                   error:NULL];
        self.greetingId.text = [[greeting objectForKey:@"id"] stringValue];
        self.greetingContent.text = [greeting objectForKey:@"content"];
    }
}];
[downloadTask resume];