How to effectively call properties in another class - Objective-C - objective-c

Question

I am a beginner with Objective-C and iOS development, and I can't figure out how to send data from one class to another without it returning null or in this case "0.0000"
I'll give the code I have-
In ClassA.h I have two properties
#interface ClassA : UIView
// This is public property!
#property (nonatomic, assign) CGFloat touchPointX;
#property (nonatomic, assign) CGFloat touchPointY;
// My test getters
- (CGFloat) touchLocationX;
- (CGFloat) touchLocationY;
#end;
Then in ClassA.m I implement these.
#implementation ClassA
- (void)baseInit {
}
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:self.frame];
if (self) {
[self baseInit];
}
return self;
}
- (id)initWithCoder:(NSCoder *)aDecoder {
if ((self = [super initWithCoder:aDecoder])) {
[self baseInit];
}
return self;
}
- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
for (UITouch *touch in touches) {
CGPoint touchLocation = [touch locationInView:self];
// Save the touch locations in our local variables.
self.touchPointX = touchLocation.x;
self.touchPointY = touchLocation.y;
[self setNeedsDisplay];
}
}
- (CGFloat) touchLocationX {
return self.touchPointX;
}
- (CGFloat) touchLocationY {
return self.touchPointY;
}
#end
Then I try to log the values in AppDelegate using some code I found on here
AppDelegate.h
#interface AppDelegate : UIResponder <UIApplicationDelegate>
#property (nonatomic, copy) ClassA *touchLocationX;
#property (nonatomic, copy) ClassA *touchLocationY;
#end
AppDelegate.m
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,
(unsigned long)NULL), ^(void) {
NSLog(#"(%#, %#)", _touchLocationX, _touchLocationY");
});
return YES;
}
I haven't been able to figure out how to do something like:
ClassA * myView = [[ClassA alloc] init];
myView = [myViewController theUIViewForClassA];
In the long run all I want is the properties to return the correct values

Answer 1

There are several ways in which data can be shared across an application.
In your example, you want to "send" touchpoints from ClassA to some other class, in this case the AppDelegate, which is fine as it demonstrates how this can work with other classes.
To accomplish this, several design patterns come to mind: Delegate Protocol, Notifications or Singleton.
I'll use the example of a singelton for convenience, because it allows us to use your AppDelegate, which is already a singleton, so this example can closely resemble your existing code.
Note that a singleton design pattern is one in which a singleton class is instantiated only once, whose methods and properties can be accessed by other classes throughout the application.
Example:
AppDelegate.h
Add a method for receiving touch events
#interface AppDelegate : UIResponder <UIApplicationDelegate>
#property (strong, nonatomic) UIWindow *window;
- (void) notifyTouchEvents:(CGFloat)touchX :(CGFloat)touchY;
#end
AppDelegate.m
Implement the method
#implementation AppDelegate
// Method for receiving touch event data from another class
- (void) notifyTouchEvents:(CGFloat)touchX :(CGFloat)touchY
{
NSLog(#"touchX: %f, touchY: %f", touchX, touchY);
}
ClassA.h
Import the App Delegate
Note: This example doesn't require touchPointX and touchPointY properties.
#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#interface ViewController : UIViewController
#property (nonatomic, assign) CGFloat touchPointX;
#property (nonatomic, assign) CGFloat touchPointY;
#end
ClassA.m
Access the AppDelegate touch notification method during touch events
#import "ViewController.h"
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
for (UITouch *touch in touches) {
CGPoint touchLocation = [touch locationInView:self.view];
// Access the AppDelegate singleton and notification method
AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
[appDelegate notifyTouchEvents:touchLocation.x :touchLocation.y];
}
}
#end
In practice, you may find that a combination of using NSNotificationCenter and a Singleton can works best. Search around for more information on using delegates and singletons with Objective C.