Change iPhone UISlider bar image

You were right to use -setMinimumTrackImage:forState: and -setMaximumTrackImage:forState: methods. What you missed is that you should provide stretchable UIImage to them, the rest is taken care of automagically:

UIImage *sliderLeftTrackImage = [[UIImage imageNamed: @"SliderMin.png"] stretchableImageWithLeftCapWidth: 9 topCapHeight: 0];
UIImage *sliderRightTrackImage = [[UIImage imageNamed: @"SliderMax.png"] stretchableImageWithLeftCapWidth: 9 topCapHeight: 0];
[mySlider setMinimumTrackImage: sliderLeftTrackImage forState: UIControlStateNormal];
[mySlider setMaximumTrackImage: sliderRightTrackImage forState: UIControlStateNormal];

You can use the same image for both the min and max parts.

The simplest solution would be to render a UIImage behind the control to represent the track. The thumbknob can be changed with:

[mySlider setThumbImage:[UIImage imageNamed:@"thumb_image.png"] forState:UIControlStateNormal];

A side-effect of this is that the track isn't rendered unless you provide your own. This, combined with the UIImage, provide you with a custom UISlider without you having to subclass anything.

Putting it all together in a modern way

If you define the UISlider in a Storyboard the best place to style the Slider is in the View's subclass. In awakeFromNib you can change the button, left and right track.

This call is deprecated in iOS 5 stretchableImageWithLeftCapWidth:topCapHeight:

- (void)awakeFromNib
{
    [super awakeFromNib];

    UIImage *thumbImage = [UIImage imageNamed:@"slider-button"];
    [self.slider setThumbImage:thumbImage forState:UIControlStateNormal];

    UIImage *sliderLeftTrackImage = [UIImage imageNamed: @"slider-fill"];
    sliderLeftTrackImage = [sliderLeftTrackImage resizableImageWithCapInsets:UIEdgeInsetsZero resizingMode:UIImageResizingModeStretch];
    UIImage *sliderRightTrackImage = [UIImage imageNamed: @"slider-track"];
    sliderRightTrackImage = [sliderRightTrackImage resizableImageWithCapInsets:UIEdgeInsetsZero resizingMode:UIImageResizingModeStretch];
    [self.slider setMinimumTrackImage:sliderLeftTrackImage forState:UIControlStateNormal];
    [self.slider setMaximumTrackImage:sliderRightTrackImage forState:UIControlStateNormal];
}

stretchableImageWithLeftCapWidth: has been deprecated since iOS 5.0. The docs say to use 'capInsets' property instead. Here's an easy way to do that:

Create three images, the min (left) track, the max (right) track, and the thumb. For this example, assume the min and max track images are 34p H x 18p W, something like this:

Create the images as usual:

UIImage *thumbImage = [UIImage imageNamed:@"sliderThumb.png"];

UIImage *sliderMinTrackImage = [UIImage imageNamed: @"sliderMin.png"];

UIImage *sliderMaxTrackImage = [UIImage imageNamed: @"sliderMax.png"];

For my 18 point wide image examples, the inner point on the left and the right can be stretched to fit the track, but the ends should have unstretchable cap sizes 17 points wide (hence the capInsets):

sliderMinTrackImage = [sliderMinTrackImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, 17, 0, 0)];

sliderMaxTrackImage = [sliderMaxTrackImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, 0, 0, 17)];

Then set the images on your UISlider as always:

[slider setThumbImage:thumbImage forState:UIControlStateNormal];
[slider setMinimumTrackImage:sliderMinTrackImage forState:UIControlStateNormal];
[slider setMaximumTrackImage:sliderMaxTrackImage forState:UIControlStateNormal];

Here is a way to add a track image that is not stretched so you can have e.g. a wedge shape in the background just as the OP asked:

Swift 3.0:

let trackImg = image.resizableImage(withCapInsets: .zero, resizingMode: .tile)
slider.setMinimumTrackImage(trackImg, for: .normal)
slider.setMaximumTrackImage(trackImg, for: .normal)

Important: make sure that the width of your slider is exactly the same as the width of the image!

You need to subclass UISlider and override:

- (CGRect)trackRectForBounds:(CGRect)bounds

Discussion You should not call this method directly. If you want to customize the track rectangle, you can override this method and return a different rectangle. The returned rectangle is used to scale the track and thumb images during drawing.

I am doing this but the back bar is not showing perfectly in iOS 5.1 but in iOS 6.0 its displaying

here is my code

 UIImage *stetchLeftTrack = [[UIImage imageNamed:@"spectrum_horizontal_bar.png"]
                                stretchableImageWithLeftCapWidth:15.0 topCapHeight:0.0];
 UIImage *stetchRightTrack = [[UIImage imageNamed:@"spectrum_horizontal_bar.png"]
                                 stretchableImageWithLeftCapWidth:15.0 topCapHeight:0.0];
 [self.slider_Sprectrum setMinimumTrackImage:stetchLeftTrack forState:UIControlStateNormal];
 [self.slider_Sprectrum setMaximumTrackImage:stetchRightTrack forState:UIControlStateNormal];