I'm developing simple MVC app in Cocoa/Objective-C. I have a strange issue (or misunderstanding) with notifications and KVO.
I have AppController object in MainMenu.xib, hence I implement awakeFromNib method where I register for NSImageView changing its image property. I add self as an observer in the following way:
// options:3 equals to new/old passed values in changeDictionary
[backgroundImageView addObserver:self
forKeyPath:#"image"
options:3
context:NULL];
The backgroundImageView is an IBOutlet in AppController connected to NSImageView.
In standard observeValueForKeyPath:ofObject:change:context method I just log the received notification.
Problem is - when i change the image value of NSImageView I get 3 notifications instead of one. Can you help me with this? Maybe I'm overlooking something in options or in generally registering observer?
UPDATE: backgroundImageView is the instance of BackgroundImageView class which is sublcass of NSImageView. I subclassed the latter one for handling drag and drop operations as drag destination. When performDragOperation: is called (the last 'state' of the dragging) it changes the value for image property with setImage between willChangeValueForKey and didChangeValueForKey.
… it changes the value for image property with setImage between willChangeValueForKey and didChangeValueForKey.
When you send an accessor message, you get KVO notifications for free with it. You should remove the {will,did}ChangeValueForKey: messages, because they're the cause of at least one of the extraneous change notifications.
Is your AppController the File's Owner of two other nibs? If so, it'll receive an awakeFromNib message for each of those, too. MainMenu plus two makes three awakeFromNib messages, which means you'll add yourself as an observer three times.
There does not seem to be any obvious problem with setting of the observer.
Have a look at how you update the image that you observe, maybe it's being modified 3 times?
Related
I'm updating a UILabel in another view using a method invoked using the NSNotification center.
What I'm finding is that it's not working, the label remains unchanged until the view is reloaded at a later point (not using the method called by nsnotification center).
The label is set to nonatomic, retain and I'm using self to bind everything to that property.
obviously all of the code (the method) that tries to update the label is located in the corresponding viewController. The method gets called (I can see that with NSLog), and all it does is self.label2.text = #"label 2 updated";
I'm able to update the text value of the label using a timer just fine, so I don't think there is a problem with the label, but rather with my understanding of threading and/or what is loaded or not at a given time.
What do you think is the problem?
PS: i WILL chose an answer even if it doesn't help me that much, so please post your wildest guesses!
First make sure that your label is not nil when you set the text.
If it's not nil, try calling setNeedsLayout on your label after setting the text (this shouldn't be necessary). Also, verify that you are on the main thread with:
[NSThread isMainThread]
If that doesn't help, use a subclass of UILabel, override setText and put a breakpoint on it to see what's going on.
When I try setting up observation of this specific key, nothing happens. Here is what I mean.
I have a standard Cocoa application, with an NSTableView, and I figured out how to change the image shown in an image view based on what cell was selected.
Now, I am trying to figure out how to disable/enable buttons by the selected index. What I mean by this, is that I have a button in the window, that is disabled on certain indexes.
SomeClass's init method
-(id)init {
if (self=[super init]) {
[arrayController addObserver:self forKeyPath:#"selectionIndex" options:NSKeyValueObservingOptionNew context:NULL];
}
}
However, when I implement the observeValueForKeyPath: method, the changes are not being picked up as I pick new indexes. As a matter of fact, the outlet shows (null) if I try logging it. However, when I add the observer in AppDelegate, AppDelegate (when specified as the observer) picks up changes.
Is there some reason my generic SomeClass object does not? Should it be done a different way?
NOTE:
I tried subclassing SomeClass as a NSWindow, then making the window's owner SomeClass, and setting up the observer in awakeFromNib, and this works, but seems like a bad way to do it.
The init method happens too early in the process, before the outlets are connected (I think). Putting the code in awakeFromNib will work correctly. This is from Apple's docs in the NSObject class reference:
The nib-loading infrastructure sends an awakeFromNib
message to each object recreated from a nib archive, but only after
all the objects in the archive have been loaded and initialized. When
an object receives an awakeFromNib message, it is guaranteed to have
all its outlet and action connections already established.
I am new with Objective-C so apologies for a dumb question.
I am opening an "options" view controller from my main view controller. Both are built in the storyboard. Before and after presenting the options controller I need to stop and start a timer on my main view controller. After the options controller is closed (a button calls dismiss) I need to send some info back to my main controller or at least let my main controller know that it needs to refresh some values.
MAIN QUESTION
What's the best way of presenting a view controller and executing some presenter's methods before and after opening?
WHAT I'VE TRIED
I found a few ways to do it, but they are all cumbersome and I assume that there must be some plausible way of doing it.
Ideally I'd like to use the segue I set up in the storyboard between the two controllers.
I managed to call the options controller programmatically by accessing the storyboard and calling instantiateViewControllerWithIdentifier. It worked but looks a bit complex.
I was not able to find a delegate method on the UIViewController to handle the dismiss event
When I was trying to access the main controller in the options controller via presentingViewController and downcasting it, I got a linkage error by including my .h file twice (not sure what are the Obj-C standards of using #define).
Appreciate your help...
For communication between ViewControllers that are weakly linked, you could use the NSNotificationCenter:
https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/Reference/Reference.html
Here you can send a message to all ViewControllers listening, which need to process some changes (for example an option to change the font size).
It's really easy to implement and it keeps certain ViewControllers less dependent on each other.
All of this can be done quite easily with storyboard and NSNotificationCenter, and NSCoding. In the viewDidLoad method of your main controller, put this code:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(receiveNotification:)
name:#"Update"
object:nil];
Then create this method in the same controller:
(void)receiveNotification:(NSNotification*)notification
{
//...
}
When you want to make the main controller update from the options controller:
[[NSNotificationCenter defaultCenter] postNotificationName:#"Update" object:self];
Also, I would suggest using NSArchiving for Basic Data Persistence. Just found this tutorial, looks pretty good.
http://samsoff.es/posts/archiving-objective-c-objects-with-nscoding
Basically, create an object that can store information, code it using nscoding, and then uncode it whenever you need it. It has worked great for me.
Hope that helps!
MAIN QUESTION What's the best way of presenting a view controller and executing some presenter's methods before and after opening?
Just in case the answers above are a bit more involved than you'd like, I'll suggest that the easiest way to execute a presenter's methods before opening is to do so in the presenter's prepareForSegue method. If you need to send data to the destination view controller, you can access its properties this way:
ViewController *destinationVC = [segue destinationViewController];
An easy way to execute the presenter's methods after opening would be:
ViewControllerSubclass *previousVC = [self presentingViewController];
And then use the class or instance to execute your class or instance methods. You could do this in the destination's viewWillAppear.
Sorry if you already knew all this; it's often difficult to surmise what level of complexity is needed.
I have run into this with almost every app I have on the market. Difference is I have never decided to go down the storyboard path.
The way I have always been able to accomplish this is to provide accessor functions between the controllers. You get past the linker issue by defining the cross defined controller as simply a UIViewController type within your options view header, then including the main view controller' header only in the .m file. Now when you call a main view controller routine from your options view, you will have to cast it to the type of your main view controller!
You will also have to provide a routine in your options view that will allow you to set the variable that will hold a pointer to your main view controller to self.
Example for your optionsView
#interface optionsViewController : UIViewController{
UIViewController * myReactiveMainViewController;
}
-(void)setMyReactiveMainViewController:(UIViewController *)controller;
No in the .m file for the optionsView
#import "myMainViewController.h"
-(void)setMyReactiveMainViewController:(UIViewController *)controller{
myReactiveMainViewController = controller;
}
In any other call back to the main view controller you will have to do this:
-(void)returnToMain{
[(myMainViewController *)myReactiveMainViewController someCall:variable];
}
This example would of course assume that your myMainViewController implements a method called "someCall" that take on input parameter.
Thanks for replies.
I ended up with
Calling prepareForSegue to execute pre-transition code
Calling performSelector on presentingViewController when releasing presented view controller.
I am sure other suggestions would work too.
I'm having trouble with a cocoa project. I'm displaying a keyboard composed of NSButtons, and I'd like that when I click on one of the keys, the label is added to a NSTextField. I have a controller that I use as a singleton, so each key "knows" how to access the controller. In the controller, I have an outlet linked to the NSTextField. When I click on a key, nothing happens. So I used something like NSLog(#"%#", [[[OakController] sharedInstance] textarea]) on a mouseDown event, and in the console output, I get (null).
Long story short, my outlet is set to nil, and I don't know why it is that way, or how to solve that...
Here's the code of the controller : https://gist.github.com/1090564. Sorry for the lack of syntax coloring.
Thanks for reading guys!
My guess is that you actually have multiple instances of OakController instead of one like you expect. Did you drag a blue cube into your IB document and change its custom class to OakController? That will allocate and initialize a new object each time. I'd guess that your sharedInstance method also allocates and initializes an instance.
Try adding an awakeFromNib method to OakController, and add a break point. Log self's pointer value. In your second case were the outlet is unexpectedly nil, also log self's pointer address.
I'm trying to use a NSProgressIndicator (indeterminate) inside of a statusbar-menu. I'm using an NSView-object as view for the menuitem, and then subviews the progress indicator to display it. But whenever i try to call the startAnimation: for the progress, nothing happens. When i try do the very same thing on a normal NSWindow it works perfectly, just not when inside a menuitem.
I'm new to both cocoa and objective-c so I might've overlooked something "obvious" but I've searched quite a bit for a workaround but without success. I found something about menuitems cant be updated while shown and that you need to use a bordeless window instead. But I have not been able to confirm this in any documentation.
Edit:
Ok, almost works now. When using the setUsesThreadedAnimation: and from a MenuDelegate's menuWillOpen and creating a new thread. This thread runs a local method:
-(void) doWork(NSProgressIndicator*) p{
[p startAnimation:self];
}
This will start the progressindicator on a random(?) basis when opening the menu. If I call startAnimation: directly without going through doWork: (still using a new thread), it never works. Doesn't setUsesThreadedAnimation: make the progress-bar create it's own thread for the animation?
Solved it by using:
[progressIndicator performSelector:#selector(startAnimation:)
withObject:self
afterDelay:0.0
inModes:[NSArray
arrayWithObject:NSEventTrackingRunLoopMode]];
Inside the menuWillOpen:, the problem seems to have been calling startAnimation: before the progressbar was finished drawing itself.
How are you referencing the NSProgressIndicator that is in the view (and the one in the window, for that matter)? For example, do you have a controller class that has IBOutlet's hooked up to the progress indicators? If you are using an IBOutlet, are you sure it's hooked up properly in the nib file?
Also, where and when are you calling startAnimation:? (We need to see some code).
One thing that can sometimes happen is that you forget to hook up an IBOutlet in the nib. Then, when you attempt to tell the object to do something in code at runtime, the IBOutlet is nil, and so what you think is a message being sent to your object is in fact, a message being sent to nil. In other words, it's just ignored, and effectively looks like it's not working.
Provided you do have a (potentially) valid reference to the UI object, the other common issue you'll see is when a developer is trying to send a message to the object at "too early" of a time. In general, init methods are too early in the controller object's lifetime to be able to send messages to user interface objects—those IBOutlet's are still nil. By the time -awakeFromNib is called, IBOutlet's should be valid (provided you hooked them up in IB) and you can then send the message to the UI object.
Have you told it to use threaded animation via -setUsesThreadedAnimation:?