Get the current value of UISlider in drawRect: method - ios

Question

I'm trying to move a point drawn in a UIView based on the value of a UISlider. The code below is for a UIView (subview ?) with a custom class (WindowView) on a UIViewController.
WindowView.h
#import <UIKit/UIKit.h>
#interface WindowView : UIView
- (IBAction)sliderValue:(UISlider *)sender;
#property (weak, nonatomic) IBOutlet UILabel *windowLabel;
#end
WindowView.m
#import "WindowView.h"
#interface WindowView ()
{
float myVal; // I thought my solution was using an iVar but I think I am wrong
}
#end
#implementation WindowView
#synthesize windowLabel;
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
- (void)sliderValue:(UISlider *)sender
{
myVal = sender.value;
windowLabel.text = [NSString stringWithFormat:#"%f", myVal];
}
- (void)drawRect:(CGRect)rect
{
// I need to get the current value of the slider in drawRect: and update the position of the circle as the slider moves
UIBezierPath *circle = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(myVal, myVal, 10, 10)];
[circle fill];
}
#end

Answer 1

OK, you need to store the slider value in an instance variable and then force the view to redraw.
WindowView.h:
#import <UIKit/UIKit.h>
#interface WindowView : UIView
{
float _sliderValue; // Current value of the slider
}
// This should be called sliderValueChanged
- (IBAction)sliderValue:(UISlider *)sender;
#property (weak, nonatomic) IBOutlet UILabel *windowLabel;
#end
WindowView.m (modified methods only):
// This should be called sliderValueChanged
- (void)sliderValue:(UISlider *)sender
{
_sliderValue = sender.value;
[self setNeedsDisplay]; // Force redraw
}
- (void)drawRect:(CGRect)rect
{
UIBezierPath *circle = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(_sliderValue, _sliderValue, 10, 10)];
[circle fill];
}
You probably want to initialise _sliderValue to something useful in the view's init method.
Also _sliderValue probably isn't the name you want to choose; perhaps something like _circleOffset or some such.