I have a button (IBAction), when I click the button a label will change (setStringValue).
Works perfectly.
Is there a way for changing a label (setStringValue) with a (void) method, so a method that is not an IBAction. Because if I call the method nothing happens? The code is illustrated below.
//IBAction method, label is changed to setLabelMethod, works perfect.
-(IBAction)setLabel:(id)sender{
[labelA setStringValue:#"Works!"];
ClassName *MyClass = [[ClassName alloc]init];
[MyClass methodSetLabel]
}
//void method, nothing happens
-(void)methodSetLabel{
[labelB setStringValue:#"Works!"];
}
What do I have to do to make this work?
Thanks!
IBAction methods are void. The reason nothing happens is different from what you think: it's not because the method is void, it's because the instance on which you call the method is wrong.
Your setLabel method creates a new instance of MyClass. That's not the class that has the real labelB displayed on your screen.
You need to call the method on the same object that owns the label and runs the setLabel: method. In Objective C this object is represented by a special variable called self. If you rewrite the method as follows
-(IBAction)setLabel:(id)sender{
[labelA setStringValue:#"Works!"];
[self methodSetLabel];
}
it should work.
Related
I am trying to change the value of the label here.
Can anyone explain me why the following method call:
[_detailLabel setStringValue:#"this is new label value"];
works if I make the call from viewDidLoad and viewDidAppear methods, but it doesn't work in the method that I created:
-(void)changeLabelValue : (NSString *) newVal {
[_detailLabel setStringValue:#"this is new label value"];
NSLog (#"Hello from changeLabelValue method");
}
Please note that when I call this method from anywhere from my code, the NSLog message IS displayed but the value of the label is not changed...
Any help is deeply appreciated.
Pointing me to resource where I can learn more on this subject will also do the trick, and will be also deeply appreciated.
Regards, John.
Make sure that changeLabelValue: is being called after viewDidLoad is called (or the view controller has been displayed). If you call it before the view is loaded, _detailLabel will be nil since it hasn't been loaded yet.
Probably a noob question, but I cannot seem to get it right at the moment. I am working on an app where I have an Actionsheet for the confirmation of some basic things. However after the delegate is called for that Actionsheet my initial calling object is released (or not initiated).
In the delegate method I then want to call a method on that object but it just not do anything from that point.
The self.inviteSponsorsFromVC is not initiated anymore in this scenario and I want to call the saveSponsorWithEmail method from it. I cannot just reinitiate it, as the object had some objects in it, it has to use.
Everything works correctly if I just remove the actionsheet and call the saveSponsorWithEmail method directly without using a delegate.
This is my delegate method:
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex {
//Get the name of the current pressed button
NSString *buttonTitle = [actionSheet buttonTitleAtIndex:buttonIndex];
if ([buttonTitle isEqualToString:NSLocalizedString(#"Send invitation", nil)]) {
ContactFromAddressBook *contactFromAddressBook = [self.tableData objectAtIndex:selectedIndex.row];
[self.inviteSponsorsFromVC saveSponsorWithEmail:contactFromAddressBook.email andName:contactFromAddressBook.fullName];
}
if ([buttonTitle isEqualToString:NSLocalizedString(#"Cancel", nil)]) {
NSLog(#"Cancel pressed --> Cancel ActionSheet");
}
}
My guess is that at in the delegate method the content of self.inviteSponsorsFromVC is nil. In Objective-C, when you send a message to nil the message is simply ignored (unlike C++, for instance, where you get a crash when you call a method on a NULL object).
As an experiment you can try either one of these:
If you use ARC, make the property self.inviteSponsorsFromVC a strong reference
If you don't use ARC, say [self.inviteSponsorsFromVC retain] at some point before you display the action sheet
Either way, what you need to do is to make sure that the object in self.inviteSponsorsFromVC is not deallocated before you invoke a method in it.
EDIT after your comment
The property declaration is good, it's got the strong attribute on it. In your InviteSponsorsFrom class, try to add a dealloc method and set a breakpoint there to see if the object is deallocated, and where the call comes from.
- (void) dealloc
{
[super dealloc];
}
Also make sure that an instance of InviteSponsorsFrom is created in the first place. I assume you have an initializer somewhere in that class where you can set a breakpoint and/or add an NSLog statement to make sure that the instance is created.
I'm working through the 'Learning Cocos2d' book, and I'm stuck on something basic.
So, theres a parent Class: GameplayLayer. In it, there's an 'init' method which creates an instance of the main character in here - 'Viking'. Viking is a subclass of 'GameCharacter', which is a subclass of 'GameObject'.
#pragma mark INIT PLAYER
Viking *viking = [[Viking alloc]
initWithSpriteFrame:[[CCSpriteFrameCache sharedSpriteFrameCache]
spriteFrameByName:#"viking.png"]];
[viking setJoystick:leftJoystick];
[viking setFireButton:fireButton];
[viking setSecondaryButton:secondaryButton];
[viking setCollisionLayer:collidableLayer]; // send collision layer to player
[viking setPosition:ccp(screenSize.width * 0.35f, screenSize.height * 0.14f)];
[viking setHealth:100];
[sceneSpriteBatchNode addChild:viking z:1000 tag:kPlayerSpriteTagValue];
Now, Viking has an update method which is called every frame by GameplayLayer. It's parent class, GameObject also has this update method, which brings up an error message if it is accidentally called - "GameObject update should be overridden'.
So in my code, I'm calling the update method of 'Viking' with the following method:
#pragma mark UPDATE_METHOD
-(void) update:(ccTime)deltaTime
{
CCArray *listOfGameObjects =
[sceneSpriteBatchNode children];
for (GameObject *tempChar in listOfGameObjects) {
CCLOG(#"engine found %#",tempChar);
[tempChar updateStateWithDeltaTime:deltaTime
andListOfGameObjects:listOfGameObjects];
}
}
So, this is supposed to call the 'updateStateWithDeltaTime' method in Viking. But somehow, it's calling the parent method in GameObject which says 'updatestate should be overridden'. How do I override the parent method?
Many thanks,
Carl
You need to cast tempChar to a Viking.
for (GameObject *tempChar in listOfGameObjects)
{
[(Viking *) tempChar updateStateWithDeltaTime:deltaTime
andListOfGameObjects:listOfGameObjects];
}
Because you're doing a for loop with fast enumeration of GameObjects, the local variable assumes that all objects are GameObjects. You need to explicitly cast tempChar to a Viking so that the program knows which class to look for the method in.
As an interesting side note, if GameObject didn't have the same method as Viking did, you would be getting a warning in XCode telling you it couldn't find the method you're asking for (because it needs to know that every object this could be called on has it).
You might want to check that the object you're calling this on is the correct class (if you only want to call this on Viking objects). You'd add if ([GameObject isKindOfClass[Viking class]) above your update method call.
I did quite a bit of research on this, but I am having a mental block about my problem. I am working on Objective-C for an iOS app
Here's my set up:
The view controller gets a text from the view (user input), and passes that text to the MethodA of the model.
The MethodA in model works on the input text and gets an output (e.g. searches google for that text). It does the search using dispatch_async method which calls the selector to MethodB within model.
MethodB parses the output and puts all the results into a NSMutableArray
My Question Here: how do I pass that NSMutableArray back to view controller so I can show it on the view?
Sorry, if the answer to my question is very simple/obvious. I am new to Objective-C
Any time I want to do async processing and that stuff needs to get back into the UI somewhere, I do one of two things:
1. Use NSNotification to tell anyone who cares that the work is complete
2. Use a delegate property on the worker and a #protocol
1 NSNotification
The model object should document in it's .h file that it fires notifications when certain things happen; such as when a portion of the model has been updated. When the ViewController initializes the model object, have it set itself up as an observer of the documented notification, and implement a callback which updates the UI.
2 delegation and #protocol
Create a #protocol such as #protocol FooModelUpdateDelegate with a method properly named such as fooObjectDidUpdate:(Foo *)object;, and then the model class has a delegate property as id<FooModelUpdateDelegate> updateDelegate and the ViewController sets itself as that delegate, and I'm sure you can figure out the rest.
I guess passing along a delegate-object that respoons to a selector-method and calling this method with the processed data will be a good way to achieve the loosley coupled structure your program deserves. Are you familiar with this concept, or shall I dig up some code-samples for you?
UPDATE: Code samples
So, I would probably use the calling class, say MyViewController, to implement the callbackMethod, myCallbackMethod as follows:
-(void) myCallbakcMethod: NSMutableArray* array {
//DoWhatever with the returned data
}
The point is to get the result passed back to this method when the computation is finished.
So in your MyViewController where you call MethodA you pass along a reference to the delegate to handle the result, namly self.
//From this:
[MyModel methodA:param1]
//To:
[MyModel methodA:param1:self]
MyModels methodA and methodB would need to add a parameter (id)delegate and pass that along between the calls.
In methodB where the data myArray is ready, do the following call:
if([delegate respondsToSelector:#selector(myCallbackMethod:)]])
[observer performSelector:#selector(myCallbackMethod:) withObject:myArray];
In your view controller:
// your controller code
...
[myModel getSearchResult:searchKeyword receiver:self action:#selector(responseReceived:)];
}
- (void)responseReceived:(MyModel *)model
{
NSArray *searchResult = model.searchResult;
[model release], model = nil;
// some view actions, for instance update your table view
...
}
In your model:
...
- (id)getSearchResult:(NSString *)searchKeyword receiver:(id)aReceiver action:(SEL)receiverAction {
self.receiver = aReceiver;
self.action = receiverAction;
// some async actions
}
In async response receiver:
...
[self.receiver performSelector:self.action withObject:self];
}
Unless I'm misunderstanding your description it sounds like your "model" class is doing more than it should. In this case it's doing at least some of the work of your controller. My suggestion would be to fold methodA and methodB into the view controller (or another controller class). Method B could still set the NSMutableArray property of "model" instance, if that's essential (or skip that step if it's not).
-(void)methodA {
NSMutableArray *someArray = ...
[self methodB:someArray];
}
-(void)methodB:(NSMutableArray*)array {
NSLog(#"%#", array);
// do something with the array, like update the view
}
But if both are methods inside the view controller why not just update the view inside the method instead of passing it to another method?
So I have this custom class with just a test method that does nslog. I am going to reuse this method many times in my app. The interface looks like this.
#interface TestViewController: UIViewController { CMImageMover * imageMover }
Then in the view did load I:
imageMover = [[CmImageMover alloc] init];
If I do:
[imageMover testMethod];
Right after the alloc and init it works in the viewDidLoad function but if I call it again from another function in the view controller nothing works and the class method does not get called.
What am I doing wrong here. Every other var I declare like NSArray/NSTimer, I do the say way and I am able to access and use it throughout my controller.
When you say "if I call it again from another function in the view controller nothing works" then first thing to check is what you are sending the testMethod. It could be nil, in which case nothing will happen. In objective C sending a message to nil does nothing. Add an NSLog to find out, e.g.
NSLog(#"imageMover object is: %#", imageOver);
[imageMover testMethod];
If the NSLog shows it is nil - or something crazy - then follow up what you are doing with the imageMover ivar.
You mention a class method in your question, but don't refer to it in your code snippets.
If you have defined testMethod as a class method it will, of course, fail if you send that message to an instance. (And it will fail noisily.) A class method would be introduced like this:
+ (void) testMethod
{
NSLog(#"CMImageMover testMethod called on Class");
}
An instance method would be introduced like this:
- (void) testMethod
{
NSLog(#"testMethod called on an instance of CMImageMover");
}
Apologies if this is all screamingly obvious to you and missing the point of the question. It's not that clear from your question where the issue lies.