Change CGContextSetLineWidth with uislider - ios

Question

I am trying to change a line stroke with UISlider, but it doesn't work. The slider value is okay but nothing is changed.
The slider is on the display and runs and give a value back on a label. I think the function is drawed on the first load and than it stops. But i don't know how fix that problem.
My .h file:
#import <UIKit/UIKit.h>
#interface Draw : UIView {
IBOutlet UISlider *slider;
IBOutlet UILabel *label;
}
- (IBAction)sliderValueChanged:(id)sender;
#end
My .m file:
#import "Draw.h"
#implementation Draw
- (IBAction) sliderValueChanged:(UISlider *)sender {
label.text = [NSString stringWithFormat:#"%.1f", slider.value];
NSLog(#"slider value = %f", sender.value);
}
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
}
return self;
}
- (void)drawRect:(CGRect)rect;
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(context, 1.0, 1.0, 0.0, 1.0);
CGContextBeginPath(context);
CGContextMoveToPoint(context, 50.0, 50.0);
CGContextAddLineToPoint(context, 250.0, 100.0);
CGContextAddLineToPoint(context, 250.0, 350.0);
CGContextAddLineToPoint(context, 50.0, 350.0);
CGContextClosePath(context);
CGContextSetLineWidth(context, slider.value );
CGContextStrokePath(context);
}
#end

Answer 1

In your method - (IBAction) sliderValueChanged:(UISlider *)sender you should call [self setNeedsDisplay] to inform the view that the contents need to be redrawn.

Answer 2

You need to tell the UI that it needs to be redrawn with the -[UIView setNeedsDisplay] message. Otherwise, it doesn't know that anything related to how the view is drawn has changed
- (IBAction) sliderValueChanged:(UISlider *)sender {
label.text = [NSString stringWithFormat:#"%.1f", slider.value];
NSLog(#"slider value = %f", sender.value);
[self setNeedsDisplay];
}