I have a design problem. Here is what I want to do: I want to constraint MKMapView to a specific region, while making it an abstraction for the view controller which want to actually work with the map.
To constraint the map view I most likely want to use the delegate method mapView:regionDidChangeAnimated: and get notified of the changes and move the map back if the region is out of my pre-determined region. However, since I want to make it generic enough I don't want the code to be in view controller. I thought I might want to sub-class MKMapView instead.
If I do that I would have a subclass of MKMapView (say, a ConstraintMapView class) which is also the delegate of MKMapView and expose the methods to constraint the region to any user of the class. But then the user of the class (say a view controller) would also expect to be a delegate of MKMapView, so I would also want to forward all delegate messages to the view controller.
To do so I need a delegate property which points to the real delegate (the view controller), but in my ConstriantMapView if I have one does that mean I'm overriding the MKMapView's setter and getter to the delegate and things get kind of complicated because inside MKMapView it could call ConstraintMapView's methods and I would give it the view controller but I really want to give it ConstraintMapView instead.
Is there a way to make this work?
Is there a better pattern for the problem that spares the controller from the nitty-gritty of moving the view back to the constrainted region?
I have done a similar proxying MKMapViewDelegate in this project; check it out:
https://github.com/mapbox/mbxmapkit
If you want to over right an Existing class, you can use "The decorator design pattern". Here is the brief explanation. http://www.raywenderlich.com/46988/ios-design-patterns Hope It helps
Related
I am basically trying to implement a video conference functionality using opentok.
I have two view controllers.
Class A that has a grey image(to tell user is offline).
It calls setsession from class B to establish the session.
uses ClassADelegate and implements setUserOnlineImage that sets the class A grey image to green.
Class B holds a method useronline.
Has a class method sharedinstance that gives out the singleton instance of the class
viewdidload ->sets a variable type = 2;
setsession ->sets a variable type = 1;
It also has a protocol "ClassADelegate"
Protocol ClassADelegate has method setUserOnlineImage.
Has a callback method session:streamCreated: that is called when a subscriber is created and setupPublisher that publishes the video
The flow is like this.
first Class A calls the setsession from Class B to establish session.
Then when a connect button is clicked the viewdidload is called and then the setupPublisher is called, view is modified loaded and all that.
Now when a subscriber tries to connect session:streamCreated: is called. here when i try to print type value it comes as one, likewise many other variables also become nil which inturn results in just giving the audio and the video isnt seen.
where as if first session:streamCreated: is called (first video is received and then connect is clicked) the flow works fine and the print statement in session:streamCreated: correctly prints type value as 2.
Someone help me figure out whats happening.
I want to know why the type value is getting changed & various other variables become nil. This is preventing the video from showing. Am i missing something? Is any other instance is been taken(but I am using a singleton instance)?
The flow you describe doesn't follow any of the known patterns of how UIViewControllers should behave. Specifically, you shouldn't need to use a singleton instance of a view controller. I think you need to reconsider the architecture, specifically the relationship between these two view controllers.
By the way, the viewDidLoad method is called on the view controller as soon as its view property becomes available, which can be before its on the screen. If the view controller is loading its view from a storyboard or nib, viewDidLoad is called as soon as that view is ready. Otherwise if you are implementing loadView, viewDidLoad is called after that method is finished.
Can you describe what Class A and Class B are trying to accomplish? It sounds like Class A is a view controller for some type of status view that shows a user's online/offline status. Class B sounds like its the OTSessionDelegate as well as the view controller for where the publisher/subscriber views will be placed. Why are these not the same View Controller? (generally view controllers are meant to control a "screenful" of content, unless you are using View Controller Containment). If these two view controllers are not on the screen at the same time, can you use a segue to pass data between them when the transition occurs?
UPDATE:
The additional information is useful for me to give you a recommendation. The thing I'm still uncertain about is if you actually do have these 2 view controllers' views on screen at the same time. This solution should work in both cases.
Outside of a segue, one view controller should not really be calling another view controller's methods directly (so calling setsession as you described is a bad idea). You shouldn't even set one as the delegate of another. At most they should share a Model object to communicate. The OTSession can be seen as a Model object. The challenging limitation is that when using the delegation pattern, only one object (you chose Class B) can be informed of updates. Rather than using the delegation pattern, I think you should use NSNotifications. In order to accomplish this, you should "wrap" the OTSession model in your own model object, setting your own model object as the delegate. Then you can notify both controllers of interesting changes as they happen. I've created a diagram to demonstrate:
In this diagram, all the downward solid arrows are owning references. VideoConference would be your own class and it would implement the OTSessionDelegateProtocol. On initialization, the VideoConference instance would create and own an OTSession instance. When something happens that Class A or Class B need to know about (such as the remote user coming online), VideoConference can send an NSNotification, which both controllers can be observers. Here is a useful article about NSNotifications.
Let's call this UIView subclass - SomeClass. This SomeClass is a part of a static library. Some customer will use this library and will add instances of this SomeClass to the cells of his (customer's) table view.
I (SomeClass) need to determine when the SomeClass "enters" screen (will become visible), and when will "exit" screen (will become non-visible).
I can use didMoveToWindow: method and then check self.window for nil. BUT, there is a problem, SomeClass gets this event, before it is actually visible, because of cells "preparation" by table view concept. And I need to know for sure, it is 100% visible by some user.
One way to determine is by using scrollViewDidScroll:. Suppose SomeClass will get scroll view by using iteration on super views and will subscribe as a delegate to found scroll view. But he will be removed by some cell that will subscribe itself as a delegate to scroll view. So I need to invent here some solution for this. For example, in Android, there is possibility to add observer, in that case SomeClass is always a listener and is not overriding any other listener. There is many to one relation in Android, not like in iOS, one to one.
The other way, I can enable some timer in didMoveToWindow: when SomeClass becomes visible, that will check each X time, its frame. The timer will be disabled, when SomeClass will go from screen.
Probably there is a way to check at low level, without using scroll view and timer on some low-level redraw method. Is it possible?
So what is the best (will use less resources / good design) method?
You can use CGRectIntersectsRect to check if the cell's frame intersects with the frame of your custom view. Aside from that, didMoveToWindow is the method you are looking for.
If as you say the table view cell will always have SomeClass as a subview, then it would make more sense to use UITableViewDelegate tableView:willDisplayCell:forRowAtIndexPath:.
I have a viewController, in which I have a view in which I draw like in Paint by tapping. In that controller I have a method to clear screen -
- (void) clearS
{
[(TouchTrackerView *)self.view clear];
}
Now, as I don't want to occupy my screen with buttons, I have button in another screen that resets application to starting position, and I want it to clear screen. That button belongs to different view controller, and among other things I want it to call my drawing view controller and ask it to wipe screen clear. So I have setup notifications, like this in draw view contoller:
[[NSNotificationCenter defaultCenter] addObserver: self selector: #selector(clearS) name:#"clearScreen" object: nil];
And like this in my view controller from where I click a button:
[[NSNotificationCenter defaultCenter] postNotificationName:#"clearScreen" object: nil];
As I understand, when the button gets clicked, notification gets posted, and method is called. And it crashes.
[(TouchTrackerView *)self.view clear]
As I understand the problem is that at the moment of method invocation the "self" variable is my non-drawing view controller, and it tries to perform clear method on view of itself, which it lacks and crashes.
How do I send the method to correct view controller?
Is there a flaw in my thinking? Maybe this can be approached in a better way?
EDIT:
I have found the problem,
[(TouchTrackerView *)self.view clear]
calls view and it is UIScrollView, and it does not support clear method. So I have made a property containing the correct view, and changed it to
[(TouchTrackerView *)self.correctView clear]
and it works like a charm.
I have chosen notification because it is only two lines of code, and I am beginner and it is hard for me to wrap my head around delegates, so I will leave this as it is, especially that it works.
At the philosophical level, while I'm sympathetic to the observations from others that you could replace the notification with a delegate pattern (or, better, delegate protocol pattern), it strikes me that this is not an appropriate example of having two controllers communicating directly to each other at all. You probably should be employing a MVC model, where the editing view controller, A, is designed for the editing of a drawing (and thus updates the model and coordinates the view) and the reset view controller, B, should just update/reset the model. If A needs to be informed of model changes, then apply a delegate-protocol pattern there, between the model and controller A. But I don't think B should be communicating with A at all.
At a practical level, there's absolutely no reason why notifications shouldn't work just fine. Unfortunately, you haven't shared enough for us to answer the question. You should share the specifics of the error message and we might be able to help you more.
I think that notifications, which are in nature a one-to-many method of communication are not good to use here. A better approach would be to hook one as the delegate of the other -> once the button is pressed and the corresponding IBAction is invoked, the delegate (in your case, the view controller you use for drawing) should get a message and perform whatever it is it needs to do.
I would avoid notifications unless you are trying to broadcast out some info that multiple objects may be interested in.
A better approach might be to create a delegate protocol for the painting view controller --
So the PaintingViewControllerDelegate Protocol may have methods like so
(void) paintingViewControllerWillClear:(PaintingViewController*)paintingViewController;
(void) paintingViewControllerDidClear:(PaintingViewController*)paintingViewController;
Now the controller with the buttons becomes the delegate to the PaintingViewController and that object provides the methods of the PaintingViewControllerDelegate protocol as needed.
I would like to know how to best possible address the following issue:
I have a single ViewController. Its view contains a great number of complex subviews (subclass of UIView). Due to the complexity some of these UIViews initialise their own UIGestureRecognisers and implement the according target actions. As I want to coordinate the gestures of various subviews I have to set the single once ViewController as the gesture's delegate.
There are various possibilities for that.
1) Initialize ALL gestures in the the viewController (this will lead to a massive viewController)
2) defining a protocol in the UIVIews (getViewController), implemented by the ViewController
#protocol CustomViewDelegate <NSObject>
#required
- (UIViewController *)getViewController;
#end
3) customise the init method of the UIViews and using the ViewController as an option.
- (id)initWithFrame:(CGRect)frame andViewController:(UIViewController *)vc;
What is the most elegant possibility to solve this issue? Is it OK to implement target actions inside a UIView object?
Thanks for your thoughts...
If you're defining custom UIView subclasses, you can invest them with as much logic as it makes sense to store local to them, give them delegate protocols to pass anything else up and, as long as you expose the delegate as an IBOutlet, you can wire up your view controller as the relevant delegate directly in Interface Builder or the UI designer part of Xcode 4. I personally think that would be the most natural way forward, since it consolidates any view-specific logic directly in the view and lets you do the wiring up where you would normally do the wiring up.
In terms of overall design, such a scheme conforms to model-view-controller provided your views are doing only view-related logic. So, for example, if you had a custom rectangular view that can take a swipe anywhere on it to reposition a pin, and the 2d position of the pin affects some other system setting, you'd be correct to catch the gesture in the view, reposition the pin and then send updates on its position down to the delegate, which would fulfil the role of controller and push the value to any other views that are affected and out to the model.
Commenting on your suggested solutions directly:
(1) this would focus all logic into the one controller; whether it's correct from a design point-of-view depends on the extent to which you're having to interrogate your custom views (in that you don't want to end up treating them as mostly data that external actors have to know how to manipulate) and the extent to which you want to reuse logic.
(2) I'm not sure I entirely understand the suggestion — what is getViewController defined on and how does it know how to respond? If it's the UIViews themselves and the view controller has to identify itself first then I'd suggest just adopting the delegate pattern wholesale rather than specialising to views and view controllers, e.g. as you may want to build compound views that tie together logic from several subviews.
(3) as a rule of thumb, the sort of things to pass to init are those that the class actually needs to know to be able to initialise; it would probably be better to use a normal property to set the controller after the fact. Or make it an IBOutlet and wire it up so that it happens automatically via the NIB.
If I'm creating a UIView programmatically and I wish to change the UIView properties (background, for example, or actually, messing with CALayers), must I place the code outside of UIView such as in the View controller? Can I put the code somewhere inside UIView?
I was checking out the CoreAnimationKioskStyleMenu example, its code is inside UIView but it's loaded from Nib and can be placed at awakeFromNib, so it doesn't seem to apply to my case.
That depends. Obviously, a good way to handle this is to use a xib file, as it is designed to hold data like this, but that isn't always the best answer for every situation.
If the view is meant to be reused frequently (like a button, or some widget) throughout the application, its best to store all that customization in a subclass of the UIView.
If its a single larger view that will always be managed by a UIViewController, you can keep some of the information in the UIViewController. However, if you end up subclassing a UIView anyway it's probably best practice to keep the data in the UIView.
As a general note, I believe its worth your time to push as much of this data into a xib using interface builder. Magic values (like colors or sizes) peppered through your code will always be a problem if you want to modify it. I have found modifying a xib to be much easier.
Actually there are some methods where you could place initialization/ customization code.
(void)willMoveToSuperview:(UIView *)newSuperview;
(void)didMoveToSuperview;
will get called as soon as u add the view as a subview to another view, at which point you already have the frame and all the properties, and you can do further customizing as you wish.
(void)layoutSubviews -- generally used for changing subviews' frames and layout organization.
Will get called each time the view needs to be redrawn by the system, or when you specifically call [self setNeedsLayout] on your UIView.
Hope this helps.