basicaly I am a C# developer but started learning Objective-C couple of last days.
Now I have to do an exercise which need to create a class and link instance variables (properties) to the UIControls values of the View (e.g. UITextField string value).
Meaning I have already implemented the desired IBOutlets in the ViewControler and inside this controler I will create an instance of the created class. In C# a class could implement the INotifyPropertyChanged interface, bind the class to the controls and notify the object when the Datasource value has changed.
Is there anything equal to this concept in Objective C? Or how can I achieve something like that, only through events when value changed for every Control?
Thank you.
Your question and grammar is a bit ambiguous but it seems to me what you want is custom (manual) property getters/setters. Try this:
#intrface AClass: NSObject {
int iVar;
}
#property (nonatomic, assign) int iVar;
#end
#implementation AClass
- (int)iVar
{
// notify object of value being read, then:
return iVar;
}
- (void)setIVar:(int)_iVar
{
iVar = _iVar;
// then notify object about property being set
}
#end
Not 100% sure what you're asking for from your question. Are you asking whether the ViewController views can auto-update when your model changes?
There are a bunch of different mechanisms for providing notifications between objects/classes/etc. The main ones are as follows (I've included IBAction which you probably know for completeness):
1) IBAction - For UI controls just as you've connected IBOutlets in your UIViewController class, you can also fire events (touch up/touch down/etc) on user interaction.
2) NSNotification - you can post these pretty much anywhere:
http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40003701
3) Key-Value Observing:
http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/KeyValueObserving/KeyValueObserving.html#//apple_ref/doc/uid/10000177i
Related
This is a common topic but, in my case there is one thing I don't understand that I can't find explained in the other asked questions.
Here is the gist of what I'm trying to do:
User clicks a button and something like this is called:
#implementation FirstClass
-(void)clickedButton
{
[SecondClass changeText];
}
And then in SecondClass is:
#implementation SecondClass
- (void)changeText {
[myLabel setText:#"text"];
}
So when the user clicks the button, the text property in myLabel in SecondClass changes to "text".
The only problem I have with this is calling [SecondClass changeText] on the existing instance of SecondClass. Since I'm not initializing the CCNodes programmatically (they are all automatically loaded upon running the app), I don't know where or how SecondClass is initialized. I'm using SpriteBuilder to build this project.
Any help would be appreciated. Thanks!
So, you have two instaces -- one with a button, and one with a label. I'm assuming they are both descendants of NSViewController or otherwise manage underlying views.
The problem is, you found no way to address second instance containing label from the method of first instance.
You need to define a property in first instance's class:
#property(weak) SecondClass *secondInstance;
And then in button clicked method:
-(void)clickedButton
{
[self.secondInstance changeText];
}
There is one issue left: who is responsible to set first instance's property that we defined? This depends on who did create both of them, probably just app delegate or enclosing controller, you know that better.
UPD: If both of the controllers are created by AppDelegate:
#import "FirstClass.h"
#import "SecondClass.h"
#interface AppDelegate ()
// case A - manual
#property(strong) FirstClass *firstInstance;
#property(strong) SecondClass *secondInstance;
// case B - declared in xib
//#property(weak) IBOutlet FirstClass *firstInstance;
//#property(weak) IBOutlet SecondClass *secondInstance;
#end
#implementation AppDelegate
...
- (void)applicationDidFinishLaunching:(NSNotification *)notification
{
// Create them
self.firstInstance = [[FirstClass alloc] init...];
self.secondInstance = [[SecondClass alloc] init...];
// Or maybe they are declared in MainMenu.xib, then you do not create them
// by hand, but must have outlets for both. See case B above.
// Connect them
self.firstInstance.secondInstance = self.secondInstance;
...
}
Note that class is not the same as an object (instance). Class is a named collection of methods, mostly for the instance. In Objective-C, class is not just a name, but an object too, so you can call a method on it (i.e. send an message to the class object). But here we always talk about objects (instances), so forget about classes – we hold objects via strong properties or weak outlets, depending on how they were created, and operate on objects, never on classes.
In objective C, the methods are either instance methods or class methods. As the name suggests, the instance methods require an instance of the class to work, whereas the class methods can be used with just the name of the class. What you need here is a class method. Just change the following line in your code:
#implementation SecondClass
- (id)changeText {
to
#implementation SecondClass
+ (id)changeText {
This will change the method from an instance method to a class method.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Subclass UIButton to add a property
I'm trying to find a way to extend UIButton so that it can have a property like
#property(assign, nonatomic) id userInfos;
without subclassing it...
Is this possible?
the button.tag is not enough in my situation...
Okay as always a better answer is available here
Subclass UIButton to add a property
This is very easy using Objective-C associated objects:
In your header:
#interface UIButton (MyCustomProperty)
#property (readwrite, retain, nonatomic) id myCustomProperty;
#end
In your implementation file:
#include <objc/runtime.h>
/* Associated objects need a unique memory location to use as a key. */
static char MyCustomPropertyKey = 0;
#implementation UIButton (MyCustomProperty)
/* Use #dynamic to tell the compiler you're handling the accessors yourself. */
#dynamic myCustomProperty;
- (id)myCustomProperty {
return objc_getAssociatedObject(self, &MyCustomPropertyKey);
}
- (void)setMyCustomProperty: (id)anObject {
objc_setAssociatedObject(self, &MyCustomPropertyKey, anObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
#end
That's it!
What you want is to create a UIButton category. Categories are designed as a way to extend the functionality of an existing class. Once created an set up, you only need to import the category and you can use its function on any instance of the class it's designed for.
You can use the objective-c runtime's associated objects functions to associate an object with another object:
void objc_setAssociatedObject(id object, void *key, id value, objc_AssociationPolicy policy)
id objc_getAssociatedObject(id object, void *key)
Also, voting to close. Duplicate of:
How to add properties to NSMutableArray via category extension?
Adding custom behavior and state to all my classes
among many others.
Edit:
I also agree with the comment on your question by #Paul.s. Attaching data to a button sounds messy. Without knowing what you're doing, I would suggest tagging the button and then have your view controller handle fetching whatever data you need based on the button's tag.
This might seem like a basic question but I'm still getting a handle on properties so please bear with me.
I have a custom NSView subclass that does its own drawing. I've set up support for different styles with a #property for setters and a typedef enum for human-readable integers. It works great, but the view won't redraw after setting its style unless I manually call setNeedsDisplay:YES on the control or resize its parent window.
Logically one would think the solution would be to simply do a [self setNeedsDisplay:YES] in the classes' setStyle: method, but I cannot for the life of me figure out how to properly do it. Whenever I try to override setStyle: it just complains, "Writable atomic property 'style' cannot pair a synthesized getter with a user defined setter".
What should be done in this situation?
Ideally, you would just declare your actual ivar/storage as a private property, then manually implement the setter setStyle:. In the implementation of setStyle:, set your private property/state, and perform your updates. So you just abstract the data from the client's interface. There are other ways to approach this, such as directly setting the ivar.
So an implementation may take the form:
MONThing.h
#interface MONThing : NSObject
- (void)setStyle:(t_style)pStyle; // << the client's interface
#end
MONThing.m
#interface MONThing ()
#property (nonatomic, assign, readwrite) t_style userStyle; // << the actual storage
#end
#implementation MONThing
- (void)setStyle:(t_style)pStyle
{
// validate parameter
// set our data
self.userStyle = pStyle;
// perform effects
[self setNeedsDisplay:true];
}
Over time, you will learn multiple ways to accomplish this, and when you would favor one over the other.
If you a setting your own setter then do not use #synthesize and #property. These are for automatic creation of the setter and getter methods. Declaring the variable in the interface file is enough.
Take a look at this question. To copy over the answer from the other question:
If you declare a #property to be atomic then do one of the following:
use #dynamic or;
use #synthesize and keep the synthesized setter and getter or;
provide a manual implementation of both the setter and the getter (without using one of the above directives).
I'm trying to add new categories to the NSArrayController class: it can select the first and the last item. I did so:
#import "NSArrayController+selectEnds.h"
#implementation NSArrayController (selectEnds)
- (void)selectFirst:(id)sender {
if (self.arrangedObjects !=nil){ BOOL ignore = [self setSelectionIndex:0];}
}
- (void)selectLast:(id)sender {
if (self.arrangedObjects !=nil){
NSUInteger lastItem = [self.arrangedObjects count]-1;
BOOL ignore = [self setSelectionIndex:lastItem];}
}
#end
I get no errors, but I would like to put this object in IB, using a blue cube and binding buttons to its "selectFirst" and "selectLast" methods.
But I'm a bit lost: which standard object to start with? A standard ArrayController? And then, which class name to choose to have the new methods listed?
Thanks for your help…
Since you didn't show NSArrayController+selectEnds.h (which is what IB actually looks at), just NSArrayController+selectEnds.m, it's hard to know exactly what you got wrong, but there's two plausible guesses.
First, if you want these new methods to be part of the interface of the class NSArrayController, you have to add them to the interface declaration, not just to the implementation.
Second, if you want Xcode (or IB) to know that these new methods are actions, you have to label them as such: in the interface, instead of marking them plain void methods, mark them IBAction methods. (In the implementation, you can do either; it doesn't matter.)
So, NSArrayController+selectEnds.h should be:
#import <Cocoa/Cocoa.h>
#interface NSArrayController (selectEnds)
- (IBAction)selectFirst:(id)sender;
- (IBAction)selectLast:(id)sender;
#end
In my iPhone application I have multiple class files, I have my main application's class files, then I have my UIView class files. I have a simple -(void) method declared in my UIView class files, how can I access it from my main applications class files?
A bit more detail: In my application a video is played, when this video finishes playing a notification is sent and actions are preformed, which I have already successfully set up, however when the movie finishes I would like a method declared in another class file to be preformed. If the method was declared in the same class file I would simply use this code: [self mySimpleVoidMethod]; But obviously this doesn't work If the method is declared in a different class file. I believe it is possible to access a method declared in a different class file, but I just haven't got a clue about how to do it. Sorry if I'm using completely incorrect terms to name things. But I am relatively new to programming all together.
You've got a couple of options, depending on your setup. Here are a few:
1) Add a reference to the class with the function (the callee) as a property in the caller's class:
Caller.h
#interface Caller : SomeObject {
Callee *myCallee;
...
}
#property(nonatomic, retain) Callee *myCallee;
Caller.m
#synthesize myCallee;
-(void)someAction {
[myCallee doSomething];
}
Something that sets up Caller after initializing both classes:
caller.myCallee = callee;
2) Use another notification event, like it looks like you already know how to do.
3) Use a protocol if you've got a bunch of different classes that Caller might need to call that all support the same method:
DoesSomething.h
#protocol DoesSomething
-(void)doSomething;
#end
Callee.h
#interface Callee : NSObject<DoesSomething> { // NSObject or whatever you're using...
...
}
-(void)doSomething;
Caller.h
#interface Caller : SomeObject {
id<DoesSomething> *myCallee;
...
}
#property(nonatomic, retain) id<DoesSomething> *myCallee;
... Then as per example 1.
4) Use performSelector to send a message to the class.
Caller.h
#interface Caller : NSObject {
SEL action;
id callee;
}
-(void)setupCallbackFor:(id)target action:(SEL)callback;
Caller.m
-(void)setupCallbackFor:(id)target action:(SEL)callback {
callee = target;
action = callback;
}
-(void)someAction {
if([callee respondsToSelector:action]) {
[callee performSelector:action];
}
I'm sure there are other ways, and there are pros and cons to each of these, but something in there should fit your needs and/or give you enough to scan the documentation to fill in any gaps...
I did a blog post a few weeks ago that outlines one way to do this. It is similar to the previous answers, and includes some sample code you can download and look at. It is based on using table view controllers, but you should be able to adapt the ideas to your application without too much difficulty.
Passing values and messages between views on iPhone
You'll need an instance of the other class, accessible from the code that runs when the movie finishes. Often, this is accomplished by storing an instance of the other class as a field in the class, set either via a "setter", or during construction. You could also use key-value observing, watching a key representing the playstate of the movie; an instance of the other class can register to observe the changes to this key.
Specifically for patterns using UIView, your UIViewController for the view will have access to it (through the view method). If your "main application's class files" have a pointer to the controller - which they probably will, setup via Interface Builder - then that's an easy way to get to a UIView instance.