Can we use blocks with Gesture Recognizers? It doesn't appear so. For example, this does not work:
UITapGestureRecognizer *tapped = [[UITapGestureRecognizer alloc] initWithTarget: self
action:^(id sender) {
}
];
Am I missing something, or are blocks just not supported by the UIGestureRecognizer class?
However, this should:
UITapGestureRecognizer *tapped = [[UITapGestureRecognizer alloc] initWithTarget:[^{
// do stuff
} copy] action:#selector(invoke)];
You shouldn't probably do this, however, since it's a private method.
Related
I am learning objective-c and do not know what this code does. I understand what UIScreenEdgePanGestureRecognizer does. However, I am confused as to what this code is doing with the UIScreenEdgePanGesture.
UIScreenEdgePanGestureRecognizer *rightRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightRecog setEdges:UIRectEdgeRight];
[rightRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightRecog];
UIScreenEdgePanGestureRecognizer *leftRecog = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[leftRecog setEdges:UIRectEdgeLeft];
[leftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:leftRecog];
This is a code pattern used to define a UIPanGestureRecognizer that checks for finger/pen touches on the devices screen edges from right inside and from left inside the screen center but will cancel any touch event happening inside the view the same time.
The recognizer binds to self.chartView to observe those gestures.
It also defines a method #selector(resetChart:) that will act (action) in case the fingers are sliding in on one side of the chartView. But the method -resetChart: will be part of the ViewController Class or View Class you defined the recogniser inside defined as (self).
UIScreenEdgePanGestureRecognizer *rightRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightRecog setEdges:UIRectEdgeRight];
[rightRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightRecog];
the above code is setting up the recognizer from the right side.
The code below does the same thing for the left side but will trigger the same method.
UIScreenEdgePanGestureRecognizer *leftRecog = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[leftRecog setEdges:UIRectEdgeLeft];
[leftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:leftRecog];
so it could be melt together like so..
UIScreenEdgePanGestureRecognizer *rightLeftRecog =
[[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:#selector(resetChart:)];
[rightLeftRecog setEdges:UIRectEdgeRight|UIRectEdgeLeft];
[rightLeftRecog setCancelsTouchesInView:YES];
[self.chartView addGestureRecognizer:rightLeftRecog];
because -resetChart: is just doing the same.
which will look like
-(void)resetChart:(UIScreenEdgePanGestureRecognizer*)gesture {
//do some stuff with the gesture or amount of fingers used.
}
I'm making a sidebar on my app so that when you swipe right it opens, I am using this code in the object I made called sidebar:
_swipeRecognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self.superview action:#selector(swiped)];
[_swipeRecognizer setDirection: UISwipeGestureRecognizerDirectionRight];
[self.superview addGestureRecognizer:_swipeRecognizer];
And this of course crashes and throws the error:
[UIView swiped]: unrecognized selector sent to instance 0x1fdbd0c0
because it's looking for the "swiped" method on self.superview when I want it to look for the method on self, but I want the gesture to be detected on self.superview.
I'm also confused, if I set initWithTarget then why do I have to do addGestureRecognizer? What's the difference between those two things?
Change this:
_swipeRecognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self.superview action:#selector(swiped)];
to:
_swipeRecognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(swiped)];
The call to initWithTarget:action: specifies the class that gets told about the gesture events. The "target" must implement the "action" method.
The call to addGestureRecognizer: specifies which view the gesture must happen on.
In many cases these are the same but in your case they are different.
if you want to handle the gesture recognized in self, at first line, you should set self as the the receiver, not self.superview:
_swipeRecognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:#selector(swiped)];
then implement the swiped action:
-(void)swiped:(UIGestureRecognizer *)gestureRecognizer {
//enter code here
}
Simply I want to add a tap gesture for a UIImageView that when the user touches, calls a method that is implemented in another class (not the same class that contains the UIImageView).
Can I do this and if so how can i do it ?
You can do that. But you need the instance of the target class (class in which method is going to execute) as delegate or something in the gesture adding class.
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc]initWithTarget:self.delegate action:#selector(doSomething)];
Here delegate will be the instance of the target class that you have to set before going to that class.
Edit
I will explain a little more. Suppose you have two view controller classes VCA and VCB. you want to call a method in VCA from VCB through a tap gesture.
in VCB.h
#property (nonatomic,assign)VCA *delegate;
in VCB.m
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc]initWithTarget:self.delegate action:#selector(doSomething)];
in VCA.m
You will present/ push VCB
VCB * viewController = [[VCB alloc]init];
viewController.delegate = self;
// push or present viewController
Declare recognizer selector on init
UITapGestureRecognizer *recognizer =
[UITapGestureRecognizer
initWithTarget:objectOfAnotherClass
action:#selector(methodImplementedOnObjectOfAnotherClass:)];
dont forget about defining number of taps (numberOfTapsRequired) and optional gesture recognizer required to fail (requireGestureRecognizerToFail:)
Link to article about selector.
One straightforward approach is calling the method of another class from the selector method of tapGesture ie.
Add UITapGestureRecogniser to the imageview
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc]initWithTarget:self action:#selector(tapRecognised)];
[imageView addGestureRecognizer:tapGesture];
Dont forget to enable the userInteraction of the UIImageView, because by default for imageview userInteraction is disabled.
you can do this like below.
imageView.userInteractionEnabled = YES;
Then in the selector of tapGestureRecogniser call the method of another class
- (void)tapRecognised
{
[next tappedOnImage];
}
Here next is the object of another class. You can use delegation also to call the method.
Hope this will help you.
here self.desired view is the view in which you want to add gesture and you should add gesture in following way
and "webViewTapped.delegate = self" means you want to call a function of the same class when user tap and you can change it to your desired function by using delegate like self.delegate
UITapGestureRecognizer *viewTapped = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(tapAction:)];
webViewTapped.numberOfTapsRequired = 1;
webViewTapped.delegate = self;
[self.desiredView addGestureRecognizer:viewTapped];
- (void)tapAction:(UITapGestureRecognizer *)sender;
{
// do your stuff here
}
My problem is similar to this one with the only exception - my ImageView appears at the same place inside the window with different content in it. Content has unique identifier which I want to use to call content-specific actions.
To quickly recap, the guy is looking for a way to pass a parameter into the selector section of the initWithTarget method.
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(handleTapGesture:itemSKU:)];
How can I pass an attribute to the handleTapGesture method or how do I read the unique value otherwise?
Any thoughts appreciated.
EDIT: The content is being pulled from a database and is different every time. The unique identifier is pretty much like an SSN - doesn't repeat.
You could set the UIImageView tag property with your content identifier, and then read that information form the selector.
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(handleTapGesture:)];
[imageView addGestureRecognizer:tapGesture];
imageView.tag = 0;
And then:
- (void)handleTapGesture:(UITapGestureRecognizer *)sender
{
if( ((UIImageView *) sender.view).tag == 0 ) // Check the identifier
{
// Your code here
}
}
Try extending the UIImageView and add whatever values (as properties) and methods you will need.
#interface UIImageViewWithId: UIImageView
#property int imageId;
#end
Then, if you want to be even MORE awesome you may want to encapsulate your behavior in this "widget"'s implementation. This will keep your ViewController nice and clean, and allow you to use this widget across multiple controllers.
#implementation UIImageViewWithId
#synthesize imageId;
- (void)handleTapGesture:(UIGestureRecognizer *)gesture {
NSLog("Hey look! It's Id #%d", imageId);
}
#end
Then just delegate the tap to the individual UIImageViewWithIds
UIImageViewWithId *imageView = [[UIImageViewWithId ... ]]
UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget: imageView action:#selector(handleTapGesture:)];
I'm using UITapGestureRecognizer because I'm using a UIScrollView that acts as a container for my UILabels. Basically I'm trying to use an action method with arguments so I can e.g. send myLabel.tag value to the action method to know what action to take depending on what UILabel has has been triggered by a tap.
One way of doing it is having as many action methods as UILabels but that isn't very "pretty" codewise. What I would like to achieve is just having one action method with switch statements.
Is this possible or will I have to do it like this (sigh):
UITapGestureRecognizer *myLabel1Tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(myLabel1Tap)];
[myLabel1Tap addGestureRecognizer:myLabel1Tap];
UITapGestureRecognizer *myLabel2Tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(myLabel2Tap)];
[myLabel1Tap addGestureRecognizer:myLabel2Tap];
UITapGestureRecognizer *myLabelNTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(myLabelNTap)];
[myLabel1Tap addGestureRecognizer:myLabelNTap];
- (void)myLabel1Tap {
// Perform action
}
- (void)myLabel2Tap {
// Perform action
}
- (void)myLabelNTap {
// Perform action
}
Add a single gesture recognizer to the view that is the superview of your various labels:
UITapGestureRecognizer *myLabelTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:#selector(myLabelTapHandler:)];
[myLabelParent addGestureRecognizer:myLabelTap];
Then when you handle the gesture, determine which label was tapped:
-(void)myLabelTapHandler:(UIGestureRecognizer *)gestureRecognizer {
UIView *tappedView = [gestureRecognizer.view hitTest:[gestureRecognizer locationInView:gestureRecognizer.view] withEvent:nil];
// do something with it
}
You can use just one UITapGestureRecognizer and in your gesture handler (your myLaberXTap), which has the syntax:
- (void)handleGesture:(UITapGestureRecognizer*)gestureRecognizer {
...
}
use gesture.view to know which view you are working on.