Ever needed to handle the tap event but needed to distinguish between tap and double tap? I guess everybody sometimes get to such issue and surprisingly prior iOS 4 there is no simple way how to do it.

With iOS4 you just call UITapGestureRecognizer and you are ready to go, so how to do it with version prior iOS4? Here you go:

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
	NSUInteger numTaps = [[touches anyObject] tapCount];
 
	if (numTaps < 2) 
	{
		[self performSelector:@selector(doSomeSingleTapAction) withObject:nil afterDelay: 0.25];
 
		[self.nextResponder touchesEnded:touches withEvent:event];
	} 
     	else 
     	{
		if(numTaps == 2) 
          	{
			[NSObject cancelPreviousPerformRequestsWithTarget:self];
 
			[self performSelector:@selector(doSomeDblTapAction) withObject:nil afterDelay: 0.25];
		}		
 
	}
}

When using affine transform to rotate views (UIIMageView in most cases, right?) for example like this:

CGAffineTransform transform = 
	CGAffineTransformMakeRotation(-b->GetAngle());
 
oneView.transform = transform;

 Make sure you then translate the object using its center property and not using the frame property, as frame is already affected by the affine transform and your image would be corrupted.

Happy coding!

Had the need to show the datetime in the toolbar next to the touch button. Just adding the UILabel as subview to the UIToolbar makes the app to crash. But there is a solution:

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UILabel* timeLabel = [[UILabel alloc] initWithFrame:CGRectMake(5, 5, 240, 20)];
timeLabel.backgroundColor = [UIColor clearColor];
timeLabel.textColor = [UIColor whiteColor];
 
// add your text here, using NSDateFormatter for example
timeLabel.text = @""; 
 
// create the bar button item where we specify the label as a view to use to init with     
UIBarButtonItem *dateTimeText = [[UIBarButtonItem alloc] initWithCustomView:timeLabel];

When setting up an image to the UIImageView for dbl resolution for retina display make sure to set the image after setting the frame of the view as initWithImage on UIImageView does not work properly.

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UIImageView *backgroundImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
[backgroundImageView setImage:[UIImage imageNamed:@"bg-wall01.jpg"]];

Where in resources we have file named "bg-wall01@2x.jpg", iOS4 does the trick for us to set the image scale to 2.0 for us (or rather 0.5 in fact).

Happy coding!

No more need to explain. How to get the current datetime and have it stored.

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// get time and rotate minute arrow and hour arrow
// get current time
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 
//  get the current hour & min
[dateFormatter setDateFormat:@"HHmm"];
NSDate *today = [NSDate date];
NSString *str = [dateFormatter stringFromDate:today];
NSString *strHour = [str substringToIndex:2];
NSString *strMin = [str substringFromIndex:2];
 
// convert hour and minute to the integer values so we can use it
NSInteger hour = [strHour integerValue];
NSInteger minute = [strMin integerValue];
 

Sometimes the image provided by the UIImagePicker is not the right size, and putting it to the UIImageView is not enough as we do need to know the size it was being fit to.

When implementing touch and gesture based interaction in your application, for example the swipe effect, you had to handle the TouchesMoved, TouchesBegan, TouchesEnded and TouchesCancelled events and handle the location of the finger and last location and so on, based on the quality of the algorithm it worked or not.

With the new SDK and with the great support from MonoTouch team, its current version of MonoTouch implements the UIGestureRecognizer and UIGestureRecognizerDelegate and related classes - UITapGestureRecognizer, UISwipeGestureRecognizer, UIRotationGestureRecognizer, UIPinchGestureRecognizer, UILongPressGestureRecognizer, UIPanGestureRecognizer. Lets have a look and few simple steps to take advantage of these common gesture implementations on the iPhone/iPad. For the demonstration we will use the swipe gesture.

First we need to have a view controller and define a Selector for the gesture recognizer. More on Selectors check the iPhone SDK, in general it is a special form of message. In MonoTouch Selectors can be consumed (fired from MonoTouch code) or exposed, being available to SDK functions and classes to be called from within.

Lets have a look at the typical implementation:

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public partial class MyViewController : UIViewController
	{
		public static Selector MySelector
		{
			get 
			{
				return new Selector("HandleSwipe");
			}
		}
///
/// and other class definition
///
	}

Please note that the Selector is defined as a static access property returning the identification of the selector via its name (HandleSwipe).

Next we need to define the gesture recognizer and its delegate and assign it to the view. We do this in the ViewDidLoad event of the controller implementation class.

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// define the gesture recognizer 
MonoTouch.UIKit.UISwipeGestureRecognizer sgr = new MonoTouch.UIKit.UISwipeGestureRecognizer();
 
// add the target to it, we put the instance itself of the controller 
// and the class instance selector
sgr.AddTarget(this, MainComicsViewController.MySelector);

// add the swipe direction, there are 4 of them (left, right, up, down). If other than one swipe is 
// needed then more recognizers must be defined and added to the view - each for the direction
sgr.Direction = UISwipeGestureRecognizerDirection.Left; 

// also assign the delegate
sgr.Delegate = new SwipeRecognizerDelegate();
 
// and last, add the recognizer to this view to take actions
this.View.AddGestureRecognizer(sgr);

Then we need our delegate class for the swipe recognizer:

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public class SwipeRecognizerDelegate : MonoTouch.UIKit.UIGestureRecognizerDelegate
	{
		public override bool ShouldReceiveTouch(UIGestureRecognizer recognizer, UITouch touch)
		{
			return true;
		}
	}

And last and finally our handler for the swipe event:

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[Export("HandleSwipe")]
public void HandleSwipe(UISwipeGestureRecognizer recognizer)
{
	// get the point of the swipe action
	PointF point = recognizer.LocationInView(this.View);
 
	// TODO: do something with the swipe
}

Well, that is all and we are done.

Happy coding!