Important: This check should always be performed asynchronously. The majority of answers below are synchronous so be careful otherwise you'll freeze up your app.

Swift

1. Install via CocoaPods or Carthage: https://github.com/ashleymills/Reachability.swift

2. Test reachability via closures

   let reachability = Reachability()!
   
   reachability.whenReachable = { reachability in
       if reachability.connection == .wifi {
           print("Reachable via WiFi")
       } else {
           print("Reachable via Cellular")
       }
   }
   
   reachability.whenUnreachable = { _ in
       print("Not reachable")
   }
   
   do {
       try reachability.startNotifier()
   } catch {
       print("Unable to start notifier")
   }
   

Objective-C

1. Add SystemConfiguration framework to the project but don't worry about including it anywhere

2. Add Tony Million's version of Reachability.h and Reachability.m to the project (found here: https://github.com/tonymillion/Reachability)

3. Update the interface section

   #import "Reachability.h"
   
   // Add this to the interface in the .m file of your view controller
   @interface MyViewController ()
   {
       Reachability *internetReachableFoo;
   }
   @end
   

4. Then implement this method in the .m file of your view controller which you can call

   // Checks if we have an internet connection or not
   - (void)testInternetConnection
   {
       internetReachableFoo = [Reachability reachabilityWithHostname:@"www.google.com"];
   
       // Internet is reachable
       internetReachableFoo.reachableBlock = ^(Reachability*reach)
       {
           // Update the UI on the main thread
           dispatch_async(dispatch_get_main_queue(), ^{
               NSLog(@"Yayyy, we have the interwebs!");
           });
       };
   
       // Internet is not reachable
       internetReachableFoo.unreachableBlock = ^(Reachability*reach)
       {
           // Update the UI on the main thread
           dispatch_async(dispatch_get_main_queue(), ^{
               NSLog(@"Someone broke the internet :(");
           });
       };
   
       [internetReachableFoo startNotifier];
   }
   

Important Note: The Reachability class is one of the most used classes in projects so you might run into naming conflicts with other projects. If this happens, you'll have to rename one of the pairs of Reachability.h and Reachability.m files to something else to resolve the issue.

Note: The domain you use doesn't matter. It's just testing for a gateway to any domain.

In general, if we want to have a clickable link in text displayed by UILabel, we would need to resolve two independent tasks:

1. Changing the appearance of a portion of the text to look like a link
2. Detecting and handling touches on the link (opening an URL is a particular case)

The first one is easy. Starting from iOS 6 UILabel supports display of attributed strings. All you need to do is to create and configure an instance of NSMutableAttributedString:

NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithString:@"String with a link" attributes:nil];
NSRange linkRange = NSMakeRange(14, 4); // for the word "link" in the string above

NSDictionary *linkAttributes = @{ NSForegroundColorAttributeName : [UIColor colorWithRed:0.05 green:0.4 blue:0.65 alpha:1.0],
                                  NSUnderlineStyleAttributeName : @(NSUnderlineStyleSingle) };
[attributedString setAttributes:linkAttributes range:linkRange];

// Assign attributedText to UILabel
label.attributedText = attributedString;

That's it! The code above makes UILabel to display String with a link

Now we should detect touches on this link. The idea is to catch all taps within UILabel and figure out whether the location of the tap was close enough to the link. To catch touches we can add tap gesture recognizer to the label. Make sure to enable userInteraction for the label, it's turned off by default:

label.userInteractionEnabled = YES;
[label addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTapOnLabel:)]]; 

Now the most sophisticated stuff: finding out whether the tap was on where the link is displayed and not on any other portion of the label. If we had single-lined UILabel, this task could be solved relatively easy by hardcoding the area bounds where the link is displayed, but let's solve this problem more elegantly and for general case - multiline UILabel without preliminary knowledge about the link layout.

One of the approaches is to use capabilities of Text Kit API introduced in iOS 7:

// Create instances of NSLayoutManager, NSTextContainer and NSTextStorage
NSLayoutManager *layoutManager = [[NSLayoutManager alloc] init];
NSTextContainer *textContainer = [[NSTextContainer alloc] initWithSize:CGSizeZero];
NSTextStorage *textStorage = [[NSTextStorage alloc] initWithAttributedString:attributedString];

// Configure layoutManager and textStorage
[layoutManager addTextContainer:textContainer];
[textStorage addLayoutManager:layoutManager];

// Configure textContainer
textContainer.lineFragmentPadding = 0.0;
textContainer.lineBreakMode = label.lineBreakMode;
textContainer.maximumNumberOfLines = label.numberOfLines;

Save created and configured instances of NSLayoutManager, NSTextContainer and NSTextStorage in properties in your class (most likely UIViewController's descendant) - we'll need them in other methods.

Now, each time the label changes its frame, update textContainer's size:

- (void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    self.textContainer.size = self.label.bounds.size;
}

And finally, detect whether the tap was exactly on the link:

- (void)handleTapOnLabel:(UITapGestureRecognizer *)tapGesture
{
    CGPoint locationOfTouchInLabel = [tapGesture locationInView:tapGesture.view];
    CGSize labelSize = tapGesture.view.bounds.size;
    CGRect textBoundingBox = [self.layoutManager usedRectForTextContainer:self.textContainer];
    CGPoint textContainerOffset = CGPointMake((labelSize.width - textBoundingBox.size.width) * 0.5 - textBoundingBox.origin.x,
                                              (labelSize.height - textBoundingBox.size.height) * 0.5 - textBoundingBox.origin.y);
    CGPoint locationOfTouchInTextContainer = CGPointMake(locationOfTouchInLabel.x - textContainerOffset.x,
                                                         locationOfTouchInLabel.y - textContainerOffset.y);
    NSInteger indexOfCharacter = [self.layoutManager characterIndexForPoint:locationOfTouchInTextContainer
                                                            inTextContainer:self.textContainer
                                   fractionOfDistanceBetweenInsertionPoints:nil];
    NSRange linkRange = NSMakeRange(14, 4); // it's better to save the range somewhere when it was originally used for marking link in attributed string
    if (NSLocationInRange(indexOfCharacter, linkRange)) {
        // Open an URL, or handle the tap on the link in any other way
        [[UIApplication sharedApplication] openURL:[NSURL URLWithString:@"https://stackoverflow.com/"]];
    }
}