I have a view with multiple dynamically created UITextfields and UISegmented controls on it (but for purposes of this question, there could also be UIButtons, UISwitches, UISliders, or anything else that inherits from UIControl). I want to preform an action whenever the user finished interacting with any of the controls, regardless of what subclass of control it belongs to. From looking at other questions, I think I want to use addTarget:action:forControlEvents: to add observers to each of my controls after they are created, but I don't know which event I'm looking for. I've tried all the ones that are listed in the Apple Docs here that seemed relevant but none of them seem to be triggered everytime. I'm looking for something like .LostFocus in VBA, but I can't seem to find out what that is - I know there is a becomeFirstResponder method to make a control active, but I can't find anything like a "lostFirstResponder" event.
I suppose I could use isKindOfClass to tell what kind of control it is, and set up my event accordingly, but that seems a little sloppy and I feel like there should be a more direct way to do it. I could also probably set up a UITapGestureRecognizer and build up something that way, but that still feels like a workaround and not really the way it's supposed to be done.
If you're willing to subclass, you can override -resignFirstResponder to detect lost "focus", and act accordingly. This is probably only useful for things like textfields which can hold first responder status, and would not work for UISwitch for instance.
Since all UIControl objects are just UIViews, you can also override touchesEnded to detect the end of interaction with these elements.. although the more accepted way is to add your dismissal handler method as an action for all the UIControlEvents that indicate end of interaction, or just UIControlEventValueChanged.
More info on UIResponder here from Apple's Documentation:
https://developer.apple.com/library/ios/documentation/uikit/reference/UIResponder_Class/Reference/Reference.html#//apple_ref/occ/instm/UIResponder/resignFirstResponder
Many UIKit classes have delegate methods that indicate when interactions have ended, for instance UITextField has a textFieldDidEndEditing method. UITextView has similar methods.
Related
Can someone please explain the high-level difference between these two methods? In particular, when would you use one over the other, and is there any overlap in terms of the purposes of these methods?
They seem like they serve the same purpose but don't appear to be related at all in documentation, and this has me confused.
beginTrackingWithTouch:withEvent:
1) subclass UIControl
2) Sent to the control when a touch related to the given event enters the control’s bounds.
3) To provide custom tracking behavior (for example, to change the highlight appearance).
To do this, use one or all of the following methods: beginTrackingWithTouch:withEvent:, continueTrackingWithTouch:withEvent:, endTrackingWithTouch:withEvent:
touchesBegan:withEvent:
1) subclass UIResponder
2) Tells the receiver when one or more fingers touch down in a view or window.
3) There are two general kinds of events: touch events and motion events.
The primary event-handling methods for touches are touchesBegan:withEvent:, touchesMoved:withEvent:, touchesEnded:withEvent:, and touchesCancelled:withEvent:.
The parameters of these methods associate touches with their events—especially touches that are new or have changed—and thus allow responder objects to track and handle the touches as the delivered events progress through the phases of a multi-touch sequence.
Any time a finger touches the screen, is dragged on the screen, or lifts from the screen, a UIEvent object is generated. The event object contains UITouch objects for all fingers on the screen or just lifted from it.
Having just run into this today, I think the key difference is that beginTrackingWithTouch and friends are only for tracking - not anything else - in particular not for target/action handling. So if you override touchesBegan, then you'd also be responsible for calling sendActionsForControlEvents when touches ended. But if you use beginTrackingWithTouch, that's handled for free.
I discovered this by implementing beginTrackingWithTouch (for a custom button control) thinking it was just a sideways replacement for handling touchesBegan. So in endTrackingWithTouch, I called sendActionsForControlEvents if touchInside was true. The end result was that the action was called twice, because first the builtin mechanism sent the action, then I called it. In my case, I'm just interesting in customizing highlighting, so took out the call to sendActionsForControlEvents, and all is good.
Summary: use beginTrackingWithTouch when all you need to do is customize tracking, and use touchesBegan when you need to customize the target/action handling (or other low-level details) as well.
If I properly understand Apple documentation:
beginTracking:
Use the provided event information to detect which part of your control was hit and to set up any initial state information
So, it's more for control state configuration.
touchesBegan:
Many UIKit classes override this method and use it to handle the corresponding touch events
This method is more for touch event handling.
I have a custom graphic that is to be displayed to a user when an event occurs. The graphic needs to be displayed on whichever viewController is currently being displayed to the user.
The way i have programmed it so far is by adding to ALL viewcontrtollers:
1) the .h file for the custom graphic class
2) an observer for the NSNotification event that is raised
3) the method which actually draws the graphic.
This doesnt feel like a very efficient way of doing things and i was wondering if anyone has a better way of doing things?
To me it sounds like you've done it in a fairly sane way. The only other way I can think is to just add the graphic to the window which would then overlay on the current view controller and you'd only need to have one object listening for the notification. You could use the app delegate for instance. But then you would have to worry about rotation of the screen yourself when adding the graphic over the top.
What you are doing is correct .. The only thing you can improve is to mauve the drawing graphics part to the custom graphic class.. (if you are not already doing so...
just Make a UIViewController variable as a member variable to the graphics class..and then set it up to the current view displaying..after you receive the notifications..and the class will itself draw the code based on the ViewController you set it up to
The reason it doesn't feel efficient is that you're duplicating a lot of code. That's more work at the outset, and it creates a maintenance headache. You should be taking advantage of the inheritance that's built into object oriented languages, including Objective-C.
If you want all your view controllers to share some behavior, then implement that behavior in a common superclass. Derive all your other view controllers from that superclass, and they'll all automatically get the desired behavior. Your superclass's initializer can take care of registering the view controller for the notification(s) that you care about, and -dealloc can unregister it. This way, you don't have to clutter up each view controller with the same repeated code, and if you want to change the code you only have to do it in one place.
I am fairly new to cocoa programming and I would like to ask if anyone can explain me how to
-(BOOL)makeFirstResponder:(NSResponder *)responder; method works. I was planning on using it for NSEvent but can anyone show me how to implement it?
I am trying to use the NSResponder class to get me a working -keyDown method.
NSResponder is one of the fundamental classes in Cocoa. Any class that can respond to events like key presses or menu commands should be a subclass of NSResponder. Each responder keeps track of it's "next responder", and each window keeps track of the object that's currently the "first responder". When an event happens in a window, a message is sent to the first responder. If that object handles the message, great. If not, it passes it along to its next responder. This is known as the "responder chain."
Normally, you don't mess much with the responder chain in Cocoa. The first responder is mostly determined by user actions, such as clicking on a control.
It doesn't make sense to 'use it for NSEvent'. NSEvent isn't a responder, but something that enables responders to do their job.
If you describe more clearly what you're trying to accomplish, I'm sure we can point you in the right direction.
You don't usually implement -makeFirstReponder:, you call it to set the input focus to a view. What is it that you really want to achieve?
I am trying to use the NSResponder class to get me a working keyDown method.
That doesn't make sense. “Use” a class?
If you want to respond to key events, you normally should do that in a view that should be capable of becoming the first responder (see the NSView docs).
See also the Event-Handling Guide, the View Programming Guide, and the video for session 145 (“Key Event Handling in Cocoa Applications”) from the WWDC 2010 session videos (which you should be able to access through your developer account even if you didn't go to WWDC last year).
Just wondering, how I go about detecting different keystrokes, and then detecting what key has been pressed I tried using this,
-(void)keyDown:(NSEvent *)event
but didnt seem to get any results. I've also had a search around but didn't find anything. I'm guessing I may have to set up something in interface builder to detect keystrokes?
I also think that it has something to do with what is selected, if its a text field something.
keyDown: method is called only for certain view and it's subviews I think. If you need all keystrokes for your app - check NSEvent class method:
+ (id)addLocalMonitorForEventsMatchingMask:(NSEventMask)mask
handler:(NSEvent* (^)(NSEvent*))block
Read upon in it Xcode documentation. I presume you're on snow leopard.
I tried using this, - (void)keyDown:(NSEvent *)event but didnt seem to get any results.
What do you mean “using” it?
You need one of your objects to respond to that message. That means you need it to be a responder, and to be in the responder chain whenever it is appropriate for the keystrokes it handles to be pressed.
Depending on what the keypress does, it may be appropriate for a single custom view to handle it; if not, it should probably be the window controller that handles it. Either one should already be in the responder chain at the appropriate times. Whichever way you go, you'll need to subclass either NSView (for a custom view) or NSWindowController.
I'm slowly learning Objective-C and Cocoa, and the only way I see so far to capture key events in Text Views is to use delegation, but I'm having trouble finding useful documentation and examples on how to implement such a solution. Can anyone point me in the right direction or supply some first-hand help?
Generally, the way you implement it is simply to add the required function to your view's controller, and set its delegate. For example, if you want code to run when the view loads, you just delegate your view to the controller, and implement the awakeFromNib function.
So, to detect a key press in a text view, make sure your controller is the text view's delegate, and then implement this:
- (void)keyUp:(NSEvent *)theEvent
Note that this is an inherited NSResponder method, not a NSTextView method.
Just a tip for syntax highlighting:
Don't highlight the whole text view at once - it's very slow. Also don't highlight the last edited text using -editedRange - it's very slow too if the user pastes a large body of text into the text view.
Instead you need to highlight the visible text which is done like this:
NSRect visibleRect = [[[textView enclosingScrollView] contentView] documentVisibleRect];
NSRange visibleRange = [[textView layoutManager] glyphRangeForBoundingRect:visibleRect inTextContainer:[textView textContainer]];
Then you feed visibleRange to your highlighting code.
It's important to tell us what you're really trying to accomplish — the higher-level goal that you think capturing key events in an NSTextView will address.
For example, when someone asks me how to capture key events in an NSTextField what they really want to know is how to validate input in the field. That's done by setting the field's formatter to an instance of NSFormatter (whether one of the formatters included in Cocoa or a custom one), not by processing keystrokes directly.
So given that example, what are you really trying to accomplish?
I've done some hard digging, and I did find an answer to my own question. I'll get at it below, but thanks to the two fellas who replied. I think that Stack Overflow is a fantastic site already--I hope more Mac developers find their way in once the beta is over--this could be a great resource for other developers looking to transition to the platform.
So, I did, as suggested by Danny, find my answer in delegation. What I didn't understand from Danny's post was that there are a set of delegate-enabled methods in the delegating object, and that the delegate must implement said events. And so for a TextView, I was able to find the method textDidChange, which accomplished what I wanted in an even better way than simply capturing key presses would have done. So if I implement this in my controller:
- (void)textDidChange:(NSNotification *)aNotification;
I can respond to the text being edited. There are, of course, other methods available, and I'm excited to play with them, because I know I'll learn a whole lot as I do. Thanks again, guys.