I am fiddling with the new UICollectionView and the UICollectionViewLayout classes. I have created a custom layout, subclassing UICollectionViewFlowLayout.
My cell sizes are changing dynamically and I set the item sizes using the delegate method below
- (CGSize)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout*)collectionViewLayout
sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
NSLog(#"SETTING SIZE FOR ITEM AT INDEX %d", indexPath.row);
return CGSizeMake(80, 80);
}
Now, under the prepareLayout method of my custom UICollectionViewFlowLayout class, I need to access these size variables so that I can make calculations how to place them and cache them for layoutAttributesForItemAtIndexPath.
However, I can't seem to find any property under UICollectionView or UICollectionViewFlowLayout to reach the custom item sizes I set in the delegate method.
Found it myself.
Implement the custom class like without omitting UICollectionViewDelegateFlowLayout
#interface SECollectionViewCustomLayout : UICollectionViewFlowLayout
<UICollectionViewDelegateFlowLayout>
and then you can call
CGSize size = [self collectionView:self.collectionView
layout:self
sizeForItemAtIndexPath:indexPath];
Looking at the various UICollectionView... header files, and watching the WWDC 2012 Session 219 - Advanced Collection Views and Building Custom Layouts video (from about 6:50 onwards), it seems the extensible delegate pattern takes advantage of dynamic typing to ensure the layout can properly access its extended delegate methods.
In short...
If you define a custom layout with its own delegate, define that delegate protocol in the layout's header file.
Your delegate object (typically the UI(Collection)ViewController that manages the collection view) should declare itself to support this custom protocol.
In the case that your layout is just a UICollectionViewFlowLayout or subclass thereof, this just means declaring conformance to UICollectionViewDelegateFlowLayout.
Feel free to do this in your class extension in the .m file if you'd rather not #import the layout header into the delegate's interface.
To access the delegate methods from the layout, call through to the collection view's delegate.
Use the layout's collectionView property, and cast the delegate to an object conforming to the required protocol to convince the compiler.
Don't forget to check that the delegate respondsToSelector: as usual prior to calling optional delegate methods. In fact, if you like, there's no harm in doing this for all methods, as the typecasting means there is no runtime guarantee the delegate will even implement the required methods.
In code...
So if you implement a custom layout that requires a delegate for some of its information, your header might look something like this:
#protocol CollectionViewDelegateCustomLayout <UICollectionViewDelegate>
- (BOOL)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)layout
shouldDoSomethingMindblowingAtIndexPath:(NSIndexPath *)indexPath;
#end
#interface CustomLayout : UICollectionViewLayout
// ...
#end
Your delegate declares conformance (I've done so in the implementation file here):
#import "CustomLayout.h"
#interface MyCollectionViewController () <CollectionViewDelegateCustomLayout>
#end
#implementation
// ...
- (BOOL)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)layout
shouldDoSomethingMindblowingAtIndexPath:(NSIndexPath *)indexPath
{
return [self canDoSomethingMindblowing];
}
// ...
#end
And in your layout's implementation, you access the method like this:
BOOL blowMind;
if ([self.collectionView.delegate respondsToSelector:#selecor(collectionView:layout:shouldDoSomethingMindblowingAtIndexPath:)]) {
blowMind = [(id<CollectionViewDelegateCustomLayout>)self.collectionView.delegate collectionView:self.collectionView
layout:self
shouldDoSomethingMindblowingAtIndexPath:indexPath];
} else {
// Perhaps the layout also has a property for this, if the delegate
// doesn't support dynamic layout properties...?
// blowMind = self.blowMind;
}
Note that it's safe to typecast here, as we're checking the delegate responds to that method beforehand anyway.
The evidence...
It's only speculation, but I suspect it is how Apple manages the UICollectionViewDelegateFlowLayout protocol.
There is no delegate property on the flow layout, so calls must go via the collection view's delegate.
UICollectionViewController does not publicly conform to extended flow layout delegate (and I doubt it does so in another private header).
UICollectionView's delegate property only declares conformance to the 'base' UICollectionViewDelegate protocol. Again, I doubt there is a private subclass/category of UICollectionView in use by the flow layout to prevent the need for typecasting. To add further weight to this point, Apple discourages subclassing UICollectionView at all in the docs (Collection View Programming Guide for iOS: Creating Custom Layouts):
Avoid subclassing UICollectionView. The collection view has little or no appearance of its own. Instead, it pulls all of its views from your data source object and all of the layout-related information from the layout object.
So there we go. Not complicated, but worth knowing how to do it paradigm-friendly way.
There is a swift version:
self.collectionView(self.collectionView, layout: self.collectionView.collectionViewLayout, sizeForItemAtIndexPath: indexPath)
Check out UICollectionView-FlowLayout on GitHub. Same idea, this just makes accessing the extended delegate methods of flowLayout a little cleaner.
For the later readers, IOS 7 has UICollectionViewFlowLayout which has defined it.
In my case everything about layout, cell layout etc. is being defined inside nib for UIViewController and separate nib for UICollectionViewCell. MyCollectionViewCell contains UIImageView with autolayout to cell with padding/margins but square-shaped.
I need round icons instead squared but don't want to take care which nib I use for iPhone or for iPad (I have separate nibs for devices and for orientation as well).
I don't want to implement #selector(collectionView:layout:sizeForItemAtIndexPath:) into my view controller.
So, inside collectionView:cellForItemAtIndexPath:
I can just use
CGSize size = cell.imageView.bounds.size;
cell.imageView.layer.masksToBounds = YES;
cell.imageView.layer.cornerRadius = size.height/2.0;
Because collectionView:layout:sizeForItemAtIndexPath: call before collectionView:cellForItemAtIndexPath: and layout done.
You can check round avatars on the bottom
Related
What is the proper way of setting up a separate delegate class for MapKit?
I have MapView class subclassing MKMapView and bare MapDelegate class conforming MKMapViewDelegate protocol having only one initializer method.
Here is the extract from MapView initialization method I use:
# MapView.m ...
#implementation MapView
- (id) initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
// [self setShowsUserLocation:YES];
[self setDelegate:[[MapDelegate alloc] initWithMapView:self]];
The only method MapDelegate class has is
# MapDelegate.m ...
- (id)initWithMapView:(MapView *)aMapView {
self = [super init];
self.mapView = aMapView;
return self;
}
Having [self setShowsUserLocation:YES]; commented, all works fine - I see the map. If I uncomment this line, my application begins to crash.
What my MapDelegate class is missing?
UPDATE 1: if I don't use a separate class MapDelegate and set just setDelegate:self - all works.
UPDATE 2: Now I understand, that the problem with [self setDelegate:[[MapDelegate alloc] initWithMapView:self]]; string is that I need MapDelegate class to live longer than it does now (delegate property has weak attribute). If I do the following:
#property (strong) id delegateContainer;
....
[self setDelegateContainer:[[MapDelegate alloc] init]];
[self setDelegate:self.delegateContainer];
...it works! Is there a better way of retaining MapDelegate life cycle along with the one of MKMapView?
Thanks!
After waiting enough for any answers that could appear here and ensuring original problematic behavior twice more times, I am posting my own answer based on the second update from the question:
The problem with [self setDelegate:[[MapDelegate alloc] initWithMapView:self]]; string is that MapDelegate class should be able to be kept alive outside of the scope of question's initWithFrame method because delegate property has weak attribute. The possible solution is to create an instance variable serving as a container for a delegate class, for example:
#property (strong) id delegateClass;
....
[self setDelegateClass:[[MapDelegate alloc] init]];
[self setDelegate:self.delegateClass];
This solves the original problem.
LATER UPDATE
Though it is possible to set MKMapView's delegate in a separate class, I now realize that such model should not be used:
Currently I always prefer to use my controllers (i.e. controller layer in MVC in general) as delegates for all of my View layer classes (map view, scroll view, text fields): controller level is the place where all the delegates of different views can meet - all situated in controller layer, they can easily interact with each other and share their logic with the general logic of your controller.
On the other hand, if you setup your delegate in a separate class, you will need to take additional steps to connect your separate delegate with some controller, so it could interact with a rest part of your logic - this work have always led me to adding additional and messy pieces of code.
Shortly: do not use separate classes for delegates (at least view classes delegates provided by Apple), use some common places like controllers (fx for views like UIScrollView, MKMapView, UITableView or models like NSURLConnection).
I think viewDidLoad would be a better place to set up the map view. It's just a guess, but perhaps the crash is due to the view not being loaded yet.
Of course subclassing MKMapView isn't recommended at all. You would generally put your map as a subview, and set the main view to be the delegate. From the docs:
Although you should not subclass the MKMapView class itself, you can get information about the map view’s behavior by providing a delegate object.
Finally, if you really want to have a separate delegate class, you don't need to set its mapView, as all delegate methods pass the map as an argument.
What I've done so far is working but I would like to know whether this is the proper way or not.
I have a map that shows an annotation when this is pressed shows a callout.
The next view shown is a table view. This table has a button to remove that annotation.
I created one property in the table View of type MKMapView. After this view is initialized when the callOut accessory is tapped, I set the MKMapView property.
When the button is pressed in the table view, I delete the annotation through the map property.
Is this the right way?
Rather than the detail view directly manipulating the parent (map) controller view's controls, a more "right" approach might be to use delegate+protocol.
Define a protocol with the methods that the map controller needs to implement (eg. deleteAnnotation, detailViewDone, etc).
The detail view will have a delegate property for that protocol and call the protocol methods via the delegate property instead of directly accessing and modifying another view's controls.
The map controller would set itself as the delegate of the detail view and actually implement the protocol methods.
This way, each controller/class doesn't have to know the internal details of how the others work and let's you more easily change how each one works internally without affecting code in the others (as long as the protocol doesn't change). It improves encapsulation and reusability.
For example, in the detail view .h, define the protocol and declare the delegate property:
#protocol DetailViewControllerDelegate <NSObject>
-(void)deleteAnnotation:(id<MKAnnotation>)annotation;
-(void)detailViewDone;
//could have more methods or change/add parameters as needed
#end
#interface DetailViewController : UIViewController
#property (nonatomic, assign) id<DetailViewControllerDelegate> delegate;
#end
In the detail view .m, wherever you handle the delete button, call the delegate method instead:
if ([delegate respondsToSelector:#selector(deleteAnnotation:)])
{
[delegate deleteAnnotation:annotation];
}
In the map controller .h, declare that it implements the protocol and declare the methods:
#interface MapViewController : UIViewController<DetailViewControllerDelegate>
-(void)deleteAnnotation:(id<MKAnnotation>)annotation;
-(void)detailViewDone;
#end
In the map controller .m, in calloutAccessoryControlTapped where you create the detail view, set the delegate property instead of the map view property:
DetailViewController *dvc = [[DetailViewController alloc] init...
dvc.annotation = view.annotation;
dvc.delegate = self;
[self presentModalViewController:dvc animated:YES];
Finally, also in the map controller .m, implement the delegate method:
-(void)deleteAnnotation:(id<MKAnnotation>)annotation
{
[mapView removeAnnotation:annotation];
//dismiss the detail view (if that's what you want)...
[self dismissModalViewControllerAnimated:YES];
}
From the documentation, the articles Delegates and Data Sources and Using Delegation to Communicate with Other Controllers may be useful as well.
I'm new to iPhone development. I've been reading several questions on how to make a google maps annotation callout window accept line breaks. Every tutorial I've read requires me to fire the mapView:didSelectAnnotationView method. But I have no idea how to trigger this. things I've tried include
putting the method in my MapViewController.m file which extends UIViewController
putting the method in a MapView.m file which extends MKMapView, then have my Mapview element in my storyboard reference it as the class to use
There's so much about xcode, objective c, and iphone development that I don't understand, so i can't tell where my problem lies.
At the moment, my map does plot my desired marker on the desired location. I just need to understand how to fire the mapView:didSelectAnnotationView and mapView:viewForAnnotation functions before I can start customizing the call out box.
Does anyone have step by step instructions on how to trigger these functions?
A bit of background
A few things to note:
You don't call mapView:didSelectAnnotationView. The MKMapView calls that function on it's delegate. In other words, when you set up an MKMapView, you tell it: "hey, listen, anytimme you need to tell me what's happening on the map, go tell this guy, he'll handle them for you". That "guy" is the delegate object, and it needs to implement mapView:didSelectAnnotationView (that's also why its name "did select", ie, it already happened, as opposed to "select"). For a simple case, the delegate is often the UIViewController that owns the MKMapView, which is what I'll describe below.
That method will then get triggered when the user taps on one of your annotations. So that's a great spot to start customizing what should happen when they tap on an annotation view (updating a selection, for instance).
It's not, however, what you want if you want to customize what annotation to show, which is what it sounds like you're actually after. For that, there's a different method just a few paragraphs earlier on the same man page: mapView:viewForAnnotation. So substitute this method if you find that mapView:didSelectAnnotationView isn't what you were looking for.
What you can do
If you got as far as a map with a marker, I'm guessing you have at least:
* a view controller (extendeding from UIViewController, and
* an MKMapView that you've added to the view for that view controller, say named mapView
The method you want to fire is defined as part of the MKMapViewDelegate protocol.
The easiest way to get this wired is to:
make your UIViewController the delegate for you MKMapView
in code, say in your viewDidLoad, of your MapViewController.m you could do mapview.delegate = self, OR
in Interface Builder, you could drag the connection from the the MKMapView delegate property to the file's owner
then, define a method on your UIViewController called mapView:didSelectAnnotationView, declaring it just like the protocol does, in your MapViewController.m file:
- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view {
// whatever you need to do to your annotation and/or map
}
Good luck!
mapView:didSelectAnnotationView is a delegate method of the map view, you can read about it here:
MKMapViewDelegate Protocol Reference
You don't need to call it, the map view will call it "by it self" and send it to every view/view controller that registered as it's delegate.
What do you need to do
Basically you need to add the MKMapViewDelegate on your .h file, what will look something like this:
#interface someViewController : UIViewController <MKMapViewDelegate>
Then in the .m file, after you instantiate the map view you should add:
mapView.delegate = self;//were self refers to your controller
From this point and on your controller will be able to "receive messages" from the map view which are the methods that you can see on the MKMapViewDelegate reference I linked to.
So to implement the mapView:didSelectAnnotationView you need to add in your .m file
- (void)mapView:(MKMapView *)mapView didSelectAnnotationView:(MKAnnotationView *)view{
//if you did all the steps this methosd will be called when a user taps the annotation on the map.
}
What is happening
What happens in the background is:
The map view has a method (Apple codded) that handles the AnnotationView touch events.
When a touch event take place it sends a "message" to all of it's delegates saying "Hey a user did Select Annotation View on this map, Do with it what ever you need".
usually it looks like that:
[self.delegate mapView:someMapView didSelectAnnotationView:someAnnotationView];
Then every view/controller that assigned itself as a delegate and implemented the method will cal this method.
Good luck
Place *place = [[Place alloc] init];
PlaceMark *placeMark = [[PlaceMark alloc] initWithPlace:place];
[self.mapView selectAnnotation:placeMark animated:YES];
I have a mkannotation located on a mapview which has a mkannotationview as well as a calloutview which when clicked goes to a child uiviewcontroller. I am updating some properties from the callout's uiviewcontroller, but after I'm finished I want to move the annotation's position on the map and change the annotation title and subtitle. How can I easily do this from the callout's uiviewcontoller? What's the most elegant way to handle this? A code sample would be great if anyone has any.
Thanks
I'd create a protocol, say MapCallBackDelegate, to handle what you want to do. This avoids tightly coupled code. Put this in your map annotation view header file
#protocol MapCallBackDelegate
-(void)updateAnnotation:(id)whatEverParamsYouWant;
#end
Then make your Map View implement this protocol. When you create your map annotation view, give it a property
#property (nonatomic, retain) id<MapCallBackDelegate> callbackDelegate;
And when you add it to your map, set that property to self
myMapAnnotationView.callbackDelegate = self;
so when you want to change the title/subtitle/position, you just invoke that message on the callbkacDelegate.
This is elegant because it reduces tightly-coupled code, allows other objects to implement the same protocol for code reuse later, and promotes information hiding in your MapAnnotationView.
Remove the annotation from the map entirely, update it, and add it to the map again. That'll ensure that the map notices that the annotations location has changed.
Although you can remove and add the annotation back as #Caleb suggests, another option is to update the coordinate property directly on the annotation you want to move.
Note that this will only work if your annotation class implements setCoordinate which can easily be done by declaring the coordinate as assign (like the built-in MKPointAnnotation class does) instead of readonly. The map view will see the change via KVO and move the annotation.
To have the child view controller tell the map view controller which annotation to change and what the new coordinates are, I recommend using delegate+protocol as another answer suggests.
The easiest way would to actually not do it from the child view controller. Maybe your needs are different from what I understand from the question, but at first blush I would do something like this:
In the header:
#interface YourController
{
...
MKAnnotation *_latestDetailViewed;
}
...
#property(nonatomic, retain) MKAnnotation *latestDetailViewed;
#end
Then in the .m something like
#implementation YourController
...
#synthesize latestDetailViewed = _latestDetailViewed;
...
-(void) dealloc
{
...
self.latestDetailViewed = nil;
[super dealloc];
}
-(void) whereverYouLaunchYourDetailScreenFrom:(MKAnnotation*)detailAnnotation
{
self.latestDetailViewed = detailAnnotation;
// then create/push your view controller
}
-(void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
if(_latestDetailViewed)
{
// Do whatever you want to the annotation here
self.latestDetailViewed = nil;
}
}
That way your changes will be made when you come back to the map. If you're really only launching a detail view for one annotation at a time, and always coming back to the map in between, then it should work without making you deal with writing a delegate protocol or firing off NSNotifications.
If I'm misunderstanding your situation let me know and I'll give you a different answer :)
Say for example you want to subclass UIScrollView to create UITableView, and you don't want to use any private interfaces.
In order to load cells, you must use the the parent's delegate (scrollViewDidScroll in UIScrollViewDelegate). Additionaly, you want to add some of your own methods to the delegate (e.g. tableView:willDisplayCell:forRowAtIndexPath:).
What I do now is:
Create UITableViewDelegate protocol which extends UIScrollViewDelegate protocol.
Create UITableViewDelegateProxy, which I set as super.delegate, in UITableView's init.
This class conforms to UIScrollViewDelegate and has a next property, which may reference an object conforming to UITableViewDelegate.
By default, it tries to respond using it's own implementation. If that isn't available, it tries with the next's implementations, otherwise it doesn't respond.
- (BOOL)respondsToSelector:(SEL)aSelector
{
if ([super respondsToSelector:aSelector])
return YES;
else if (self.next)
return [self.next respondsToSelector:aSelector];
else
return NO;
}
- (void)forwardInvocation:(NSInvocation *)anInvocation
{
// self did not respond to selector
if (self.next)
[anInvocation invokeWithTarget:self.next];
else
[self doesNotRecognizeSelector:anInvocation.selector];
}
So up to now, this class is totally transparent and future-proof if UIScrollViewDelegate is extended.
Then I add implementations for some of the delegate methods to change the default behavior or add some more behavior (e.g. call next's tableView:willDisplayCell:forRowAtIndexPath: in scrollViewDidScroll).
Override delegate and setDelegate: in UITableView to return and set super.delegate.next instead of super.delegate. I also change the protocol from UIScrollViewDelegate to UITableViewDelegate.
This works OK if UIScrollView is accessing the delegate via it's ivar directly. If it uses the getter, it will not return our proxy, but instead the delegate set by the user of the class. Either way, we can't rely on this behavior. (fyi: In UIScrollView, it goes through the getter sometimes, but not always).
So if we stay with this example, the question is: how could we implement UITableView, exactly as it is today, ourselves?
You can't do it and preserve the contract, which is unfortunate. It's somewhat unusual that UITableView inherits from UIScrollView; on the desktop Cocoa side of things, NSTableView does not inherit from NSScrollView.