iOS: Can I override pinch in/out behavior of UIScrollView? - iphone

I'm drawing a graph on a UIView, which is contained by a UIScrollView so that the user can scroll horizontally to look around the entire graph.
Now I want to zoom the graph when a user pinches in with two fingers, but instead of zooming in a view with the same rate for X and Y direction, I want to zoom only in the X direction by changing the X scale, without changing the Y scale.
I think I have to catch the pinch in/out gesture and redraw the graph, overriding the default zooming behavior.
But is there a way to do this?
I've been having a very difficult time to catch the pinch gesture on the UIScrollView, as it cancels the touches when it starts to scroll. I want the zooming to work even after the UIScrollView cancels the touches. :(
Thanks,
Kura

Although you cannot delete the existing pinch gesture recognizer, you can disable it and then add your own:
// Disable existing recognizer
for (UIGestureRecognizer* recognizer in [_scrollView gestureRecognizers]) {
if ([recognizer isKindOfClass:[UIPinchGestureRecognizer class]]) {
[recognizer setEnabled:NO];
}
}
// Add our own
UIPinchGestureRecognizer* pinchRecognizer =
[[UIPinchGestureRecognizer alloc] initWithTarget:self
action:#selector(pinch:)];
[_scrollView addGestureRecognizer:pinchRecognizer];
[pinchRecognizer release];
Then in
- (void) pinch:(UIPinchGestureRecognizer*)recognizer { .. }
use
[recognizer locationOfTouch:0 inView:..]
[recognizer locationOfTouch:1 inView:..]
to figure out if the user is pinching horizontally or vertically.

You should instead access the gestureRecognizers (defined in UIView), there are several of them being used by the scroll view,
figure out which one is the pinch recognizer and call removeGestureRecognizer: on the scroll view, then create your own and have it do the work, add it back with addGestureRecognizer:.
these are all public API,
the recognizers and what order they are in are not (currently),
so program defensively when accessing them
(this is a perfectly valid way to manipulate UIKit views, and Apple won't/shouldn't have issues with it - though they will not guarantee it works in any future release)

You should be able to subclass UIScrollView and override the touchesBegan: method. Don't call [super touchesBegan:] but instead, adjust the zoom as you like:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
//Anything you want. Probably you would want to store all the touches
//or their values, so that you can compare them to the touches
//in the touchesEnded: method,
//thus letting you know what the pinch amount was
}
If you like, you can judge whether it's a pinch or not, and if it's not, call the super method, and only handle it yourself for custom pinches.

Edsko & bshirley answers are good, but they don't tell where to place the code.
First, I placed it in viewDidLoad method, but no Pinch Gesture Recognizer was found in the scrollview (maybe because my scrollview is an IBOutlet).
Then I tried in viewWillAppear or viewDidAppear and the UIPinchGestureRecognizer was here.

Related

ios UISwipeGestureRecognizer calculate offset

I'm adding swipe gesture recognizer to my application
- (void)createGestureRecognizers
{
//adding swipe up gesture
UISwipeGestureRecognizer *swipeUpGesture= [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(handleSwipeUpGesture:)];
[swipeUpGesture setDirection:UISwipeGestureRecognizerDirectionUp];
[self.view addGestureRecognizer:swipeUpGesture];
[swipeUpGesture release];
}
And the method to handle swipe events:
-(IBAction)handleSwipeUpGesture:(UISwipeGestureRecognizer *)sender
{
NSLog(#"handleSwipeUpGesture: called");
}
How can I calculate offset here? to move the view?
The UIGestureRecognizer abstract superclass for UISwipeGestureRecognizer has the foollowing methods
- (CGPoint)locationInView:(UIView *)view
- (CGPoint)locationOfTouch:(NSUInteger)touchIndex inView:(UIView *)view
Which allow you to know the position of the gesture in the view, but this is a discrete gesture recognizer (which will fire at a given "translation" or "offset" whatever you want to call it, which you cannot control). It sounds like you are looking for continuous control, for this you want a UIPanGestureRecognizer which has the following methods (which do the translation calculations for you)
- (CGPoint)translationInView:(UIView *)view
- (void)setTranslation:(CGPoint)translation inView:(UIView *)view
- (CGPoint)velocityInView:(UIView *)view
You will then get quick fire callbacks while the gesture is continuously unfolding.
UISwipeGestureRecognizer is for detecting a discrete swipe gesture - it only fires your action one time after a swipe has completed - so if youre asking about the offset or distance the finger moved, you'd probably want to look at creating a subclass of UIGestureRecognizer or using UIPanGestureRecognizer to get continuous gesture info. Not sure about what exactly you're looking to do, but a UIScrollView might be in order as well...
Check out the apple docs for gesture recognizers.

Two fingered swipe v. one fingered drag in iOS

In my app I have a UIView derived class Canvas that uses touchesBegan: withEvent:, touchesMoved: withEvent:, and touchesEnded: withEvent: to draw in the canvas. I also want to use a swipe to load the previous (or next) canvas in an array. I tried setting up the following gesture (and a similar one for right):
UISwipeGestureRecognizer* leftSwipe = [[UISwipeGestureRecognizer alloc] initWithTarget: self action: #selector(pageFlipNext)];
leftSwipe.direction = UISwipeGestureRecognizerDirectionLeft;
leftSwipe.numberOfTouchesRequired = 2;
[_canvas addGestureRecognizer: leftSwipe];
[leftSwipe release];
But my two fingered swipes are still being treated as one-fingered drawing instructions.
How do I get my app to handle the two-fingered swipe correctly?
First of all, I would get started verifying whether _canvas.multipleTouchEnabled is set to YES. If it isn't, set it to YES.
You might also want to consider
leftSwipe.delaysTouchesBegan = YES;
This will delay the touches to be sent to the _canvas until the gesture fails. You can also use a UIPanGestureRecognizer and do something like this,
[pan requireGestureRecognizerToFail:leftSwipe];
I think that you can use UIPanGestureRecognizer
UIPanGestureRecognizer is a concrete
subclass of UIGestureRecognizer that
looks for panning (dragging) gestures.
The user must be pressing one or more
fingers on a view while they pan it.

How to implement touch events in uiwebview?

I have tried various solutions provided on this site and others to implement touch events on uiwebview. But still I am not able to do this. Actually, i have created a article reader application. Here, I have added a uiwebview on the normal uiview. Now, I want to trace some user touch events on that particular webview.
When I do this on normal view, it works perfectly. But if I try it on webview. it stops working.
The solutions I tried before are
implementing touch methods like
touchbegan
touchended
touchmoved
touch cancelled
2 implementing uigesturerecognizer
3 implementing window touch events like send event
Now If anyone can help me or tell me where I am doing wrong or a new solution(other than this), then I will be thankful.
Put a transparent UIVIew on top of your UIWebView to capture touches. You can then act on them or optionally pass them down to the UIWebView using the touchesBegan deletage method.
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
[self.myUIWebView touchesBegan:touches withEvent:event];
}
Check this previous post for details: iOS - forward all touches through a view
I subclassed UIWebView and just "leeched" onto its gesture recognizers in subviews 2 levels deep (you could go recursively but thats enough for iOS6-7).
Then you can do whatever you want with the touch location and gesture recognizer's state.
for (UIView* view in self.subviews) {
for (UIGestureRecognizer* recognizer in view.gestureRecognizers) {
[recognizer addTarget:self action:#selector(touchEvent:)];
}
for (UIView* sview in view.subviews) {
for (UIGestureRecognizer* recognizer in sview.gestureRecognizers) {
[recognizer addTarget:self action:#selector(touchEvent:)];
}
}
}

Always animate UIView to user's tap location

I have a UIView that I want to animate to the position where the user's finger currently is.
So, when the touch begins, it has to animate to the tap location.
When the touch moves, it has to adjust its destination to the new location.
When the touch ends, it has to finish the animation to the last tap location.
I tried several things but none worked out. I tried creating a new animation with beginsFromCurrentState in touchesMoved, but that didn't work too.
It seems you're complicating this a little bit. If you are implementing touchesMoved, you are wanting a drag. If you are more interested in a tap, then touchesEnded is where you want to implement this. Either way, you just need to get the location in view and update your UIView's center based upon that location. If you wrap the change to the center value in a UIView animation block, it will animate to the position as it updates.
If you are using iOS 3.2 or later, you can use gesture recognizers which makes this pretty trivial:
// In viewDidLoad or some such
UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc]
initWithTarget:self action:#selector(viewWasTapped:)];
[[self view] addGestureRecognizer:tapRecognizer];
Then declare your action selector:
- (void)viewWasTapped:(UITapGestureRecognizer*)recognizer
{
CGPoint location = [recognizer locationInView:[self view]];
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:1.0f]; // take a second to animate
[viewToMove setCenter:location];
[UIView commitAnimations];
}
This will animate the view from one location to another. This is referred to as implicit animation. Using Core Animation classes such CAKeyframeAnimation or CABasciAnimation would be explicit animation.
Need a few more details for this.. But are you sure you are using touchesBegan, touchesMoved and touchesEnded from the appropriate view (ie not the view you want to move)? Also make sure the userInteractionEnabled = YES. Try logging the touches from touchesBegan to make sure you are receiving the touches.
Or you might want to just check out Apples MoveMe sample code at https://developer.apple.com/library/ios/#samplecode/MoveMe/Introduction/Intro.html where they have solved all those problems for you.

How to detect touch on UIImageView inside UIScrollview?

I have a UIScrollview in my app and I populate it with LOTS of UIImageViews approx 900. They are all very small and consist of only two different images over and over again.
Now I am having a lot of trouble detecting a touch on one of these UIImageViews.
I have assigned them all a unique TAG so as to be able to distinguish between them but I am really struggling to detect the touch.
The goal is just to be able to change the image of the touched UIImageView.
Due to the large amount of views involved a simple loop checking touch coordinates against each UIImageViews frame is just hanging my app.
Does anyone have any suggestions?
Thanks in Advance.
Ben
In my case the easiest way to do it was adding a gesture recognizer:
UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(singleTapGestureCaptured:)];
//Default value for cancelsTouchesInView is YES, which will prevent buttons to be clicked
singleTap.cancelsTouchesInView = NO;
[myScrollView addGestureRecognizer:singleTap];
Then use this method to capture the touch:
- (void)singleTapGestureCaptured:(UITapGestureRecognizer *)gesture
{
CGPoint touchPoint=[gesture locationInView:myScrollView];
}
UIImageView has touch processing turned off by default. To change that set userInteractionEnabled to YES (see the docs here http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIImageView_Class/Reference/Reference.html)
Also if you want to know which view was hit in a view hierarchy you can use hitTest:withEvent: (see docs in UIView) which will be much faster than you looping through the hierarchy.
On a wider note I don't think having 900 UIImageView's on the screen all at once is going to be a good long term strategy. Have you investigated drawing the screen's content via CoreGraphics?
The best way to solve this issue is to subclass UIScrollView, add touchesBegan etc methods to it.
#interface MyScroll : UIScrollView
{
}
You could easily implement this method on the UIImageView object:
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
if ([self pointInside:point withEvent:event]) {
//You clicked inside the object
}
return [super hitTest:point withEvent:event]
}
Use the return to tell the application the next touch responder (such as the uiimageview or the scrollview).