Drawing with Drawrect - ios

Question

dear objectiveC masters,
I'm a newbie apple programmer and since I'm currently taking a master degree in math education, I want the make a thesis on making apps that based on math education..
Right now, I'm trying to make an iPad app that draws a sine function and then transforms the sine function. I draw the sine graph by overriding the drawrect function in a custom uiview class and load it to a uiview object. The sine function is drawn nicely on a context, along with grids and axes that are drawn on different contexts.
I put several sliders and then plan to use the sliders to change the variables in the uiview class that i use for drawing. Now here's the problem, I realize that I can't access the variables in the viewcontroller from the custom uiview class, and I suspect that I may have mistakenly used the wrong paradigm in writing the whole program.
Can someone help me to clear the confusion here? It doesn't have to be in the exact codes but more to the big pictures of how I should draw and redraw the sine function on a view object whilst changing the variables of the sine function through sliders.
Thank you for your kind help :)
Chandra from Indonesia.

Answer 1

There are two ways to solve this:
Instead of letting the UIView ask the values from the UIViewController, you can also push the values to the UIVIew the moment one of the sliders changes. This way the UIView does what it should do: draw what the ViewController asks him to.
Think of a function like redrawUsingNewValues: that you implement in the UIView and you call from the UIViewController.
Use delegation. If you really want the UIView to be in control, you can give it a pointer to the UIViewController using delegation. That way the UIView doesn't own the UIViewController, but you can get the values you want.
An introduction on delegation can be found here: Delegation and the Cocoa Frameworks
Good luck on your program!

Answer 2

A method in the UIViewController should recognize when the slider values changes
the same method should trigger another methode within the UIViewController to update/recalculate the sine function values (e.g. creating an value array)
at the end of the update-methode the necessary values are transferred to the UIView via an outlet from UIViewController to the UIView (the UIView is an property of the UIViewController)
the UIView is drawing the new sine-function in draw rect
Edit 1:
your ViewController.h:
#import <UIKit/UIKit.h>
#class YourGraphUIView; // that's you view where you draw
#interface ResultViewController: UIViewController
#property (weak, nonatomic) IBOutlet UISlider *valueFromSlider; //bound to your UISlider
#property (weak) IBOutlet YourGraphUIView *yourGraphUIView; //bound to your costumUIView
#property (nonatomic, retain) NSNumber *graphValue;
- (IBAction)takeSliderValue:(id)sender; //bound to your UISlider
#end
your ViewController.m:
#import "ResultViewController.h"
#import "YourGraphUIView.h"
#interface ResultViewController ()
#end
#implementation ResultViewController
#synthesize yourGraphUIView, valueFromSlider, graphValue;
- (IBAction)takeSliderValue:(UISlider *)sender{
graphValue = [NSNumber numberWithDouble:[(double)sender.value]]; //takes value from UISlider
yourGraphUIView.graphValue = graphValue; //gives the value to the yourGraphUIView
[self.yourGraphUIView setNeedsDisplay] //<--- important to redraw UIView after changes
}
end
your YourGraphUIView.h:
#import <UIKit/UIKit.h>
#interface YourGraphUIView : UIView
#property(nonatomic, retain)NSNumber *graphValue;
- (void)drawRect:(CGRect)dirtyRect;
#end
your YourGraphUIView.m:
#import "YourGraphUIView.h"
#implementation YoutGraphUIView
#synthesize graphValue;
//... init, draw rect with using the graphValue for calculating and updating the graph
end;
I hope this helped. You should have a look how to build the GUI and how to connect the UIViews. You need to set the custom classes for the ViewController and the YourGraphUIView as well. Good luck!