UISlider Thumb Animation in iphone sdk - ios

Question

How to animate uislider thumb animation in iphone sdk?
Please check my code below.
Create Slider
slider = [[UISlider alloc] initWithFrame:CGRectMake(0.0, 300.0, 320.0, 3.0)];
[[UISlider appearance] setThumbImage:[UIImage imageNamed:#"chnavigate-1.png"] forState:UIControlStateNormal];
UIImage *clearImage = [[UIImage imageNamed:#"png1.png"] stretchableImageWithLeftCapWidth:14.0 topCapHeight:0.0];
[slider setMinimumTrackImage:clearImage forState:UIControlStateNormal];
[slider setMaximumTrackImage:clearImage forState:UIControlStateNormal];
[slider addTarget:self
action:#selector(sliderAction:)
forControlEvents:UIControlEventValueChanged];
slider.minimumValue=0.0;
slider.maximumValue=3.6;
[slider setValue:0.0];
//slider.value = 0.1f;
[slider setContinuous:YES];
//slider.thumbTintColor=[UIColor redColor];
[slider addTarget:self action:#selector(sliderAction:) forControlEvents:UIControlEventValueChanged];
Animation Code below:
[UIView animateWithDuration:0.3 delay:1.3 usingSpringWithDamping:0.1 initialSpringVelocity:1.0 options:UIViewAnimationOptionAllowUserInteraction animations:^{
//Animations
slider.frame = CGRectMake(slider.frame.origin.x,slider.frame.origin.y - 20,slider.frame.size.width,slider.frame.size.height);
}
completion:^(BOOL finished) {
//Completion Block
}];
This animation gives animates full silder. My requirement is animate onlu slider thumb image only.
Hemp me.
Thanks...

Answer 1

I did some poking around and wrote some test code, and my conclusion is that you can't animate the thumb image of UISlider, except for the one following situation: when the thumb is in the exact middle of the slider and not moving.
In that one situation you can make a UIImageView (since you can't animate UIImage) with your thumb image of choice (you have to make one, there's no way to get a pointer to the default thumb image as of iOS 7+), place it as a subview on your UISlider over the default thumb image, and animate that.
HOWEVER, as soon as the thumb is in a non-centered position, you butt your head against the fact that there is no way to get a UISlider's track size, and the track size is smaller than the UISlider's frame.size.width by some amount/factor/magic number that's hidden in Apple's implementation.
The two approaches I thought of are as follows:
Respond to UISlider UIControlEventValueChanged notifications and recalculate the position of the UIImageView overlaying UISlider's thumb image. However, if you base this calculation on the UISlider's frame.size.width, as soon as you move off the the centered position, there will start to be an offset between the default thumb and your UIImageView. The further you move off-center the greater this offset becomes, returning to 0 (perfectly lined up) when you move back to center.
Let the UIImageView respond independently to touch events. However, as before, since there is no way of getting UISlider's track size, while you could lock the UIImageView to an initial y value and let it move along the x, there is no way to know what the maximum or minimum x values would be.
In either case, you could trail and error your way to a value for the difference between the UISlider's frame width and the track's width that might work for a given situation in a given version of iOS, but there's no guarantee another situation or an update won't break that.
My solution, if this was essential, would be to create my own version of UISlider as a subclass of UIControl that allowed such things.