Ios – Change UIslider thumb image while sliding

iosobjective cuislider

I want to change UISlider thumb image during the slide.
Basically to set thumbImage acording to the value.
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The idea was to rotate the image according to the value and set it to the thumb.
So I tried to set the thumb image by overriding 

-(BOOL)continueTrackingWithTouch:(UITouch *)touch withEvent:(UIEvent *)event
 [self setThumbImage:[self imageRotatedByDegrees:50] forState:UIControlStateHighlighted];

and I also tried the same thing when I added an action to my slider.
Unfortunately in both implementations the image simply disappears.
Do you think it possible to achieve in the way I do it?
If NO please explain and suggest an alternative way (hopefully not one that will customize and replace the whole slider)
If Yes I will really appreciate code sample.
The more close answer that I found here

Thanks a lot.

Best Answer

I found a mistake in my Code. Apparently I was releasing one of the image before calling CGContextDrawImage. (I still need to improve my GUI appearance to make it more nice, for instance to make the track image as I planed I made the original one transparent and added the as subview the one I need.)

- (id)initWithFrame:(CGRect)frame
 {
self = [super initWithFrame:frame];
if (self) {
    self.thumbImage = [self imageWithImage:[UIImage imageNamed:@"IconForSlider.png"] scaledToSize:CGSizeMake(frame.size.height, frame.size.height)];
    size = self.thumbImage.size.height;
    [self setThumbImage:[self imageRotatedByDegrees:0] forState:UIControlStateNormal];
    [self addTarget:self action:@selector(changeValue) forControlEvents:UIControlEventValueChanged];

}
return self;
}

-(void)changeValue{
NSLog(@"ChangeValue");
[self setThumbImage:(UIImage *)[self imageRotatedByDegrees:(self.value * 100*(10/9))] forState:UIControlStateHighlighted];
[self setThumbImage:(UIImage *)[self imageRotatedByDegrees:(self.value * 100*(10/9))] forState:UIControlStateNormal];
 }

#pragma mark ImageResize
- (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
 }

 #pragma mark Rotate

- (UIImage *)imageRotatedByDegrees:(float)degrees
 {
NSLog(@"ImageRotateByDegres");
static float Prc = 0.6;
degrees = (degrees > 90)? 90: degrees;

UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,size,size)];
CGSize rotatedSize = rotatedViewBox.frame.size;

 // Create the bitmap context

UIGraphicsBeginImageContextWithOptions(rotatedSize , NO, 0.0);
CGContextRef bitmap = UIGraphicsGetCurrentContext();
UIColor *color = [self.colorsArray objectAtIndex:lround(self.value*100)];
[color setFill];
CGContextRef bitmap = UIGraphicsGetCurrentContext();

[[UIColor colorWithRed:((139 + (116/100)*self.value*100)/255.0) green:141/255.0f blue:149/255.0f alpha:1.0f] setFill];
// Move the origin to the middle of the image so we will rotate and scale around the center.
CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

// Rotate the image context
CGContextRotateCTM(bitmap,DEGREES_TO_RADIANS(degrees));

CGContextClipToMask(bitmap, CGRectMake(-1*size/ 2, -1*size / 2, size, size), [self.thumbImage CGImage]);
CGContextAddRect(bitmap, CGRectMake(-1*size/ 2, -1*size / 2, size, size));
CGContextDrawPath(bitmap,kCGPathFill);
 //Prc and 1.07 are for better view
CGContextDrawImage(bitmap, CGRectMake(-1.07*size/2*Prc, -1*size/2*Prc,size*Prc,size*Prc), [[UIImage imageNamed:@"ActiveIcon.png"]CGImage]);

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;

 }

with some help from this link I create an array of colours for my slider Get Pixel Color of Uiimage

- (UIColor *)GetColorAtValue:(float)value{

long pixelInfo = (long)floorf(_sliderImage.size.width  * _sliderImage.size.height/2 + _sliderImage.size.width * value) * 4  ;

UInt8 red = data[pixelInfo];         // If you need this info, enable it
UInt8 green = data[(pixelInfo + 1)]; // If you need this info, enable it
UInt8 blue = data[pixelInfo + 2];    // If you need this info, enable it
//UInt8 alpha = data[pixelInfo + 3];     // I need only this info for my maze game
//CFRelease(pixelData);

UIColor* color = [UIColor colorWithRed:red/255.0f green:green/255.0f blue:blue/255.0f alpha:1]; // The pixel color info

return color;

}

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