Is a Right-to-Left progress bar possible on iOS?

I've tried sending [UIProgressView setProgress] negative values, and that doesn't work.

Is there some other wa开发者_运维知识库y to get a progress bar that fills from the right-hand end?

You could try setting the transform property of your UIProgressView to a new CGAffineTransform that rotates the view by 180 degrees and flips it vertically (to preserve the "shininess") (see CGAffineTransformMake() and CGAffineTransformRotate()).

Something along the lines of:

UIProgressView *pv = [[UIProgressView alloc] initWithProgressViewStyle:UIProgressViewStyleBar];
pv.frame = CGRectMake(10, 100, 300, 11);
CGAffineTransform transform = CGAffineTransformMake(1, 0, 0, -1, 0, pv.frame.size.height); // Flip view vertically
transform = CGAffineTransformRotate(transform, M_PI); //Rotation angle is in radians
pv.transform = transform;
pv.progress = 0.5;

You can rotate the UIProgressView:

progressView.transform = CGAffineTransformMakeRotation(DegreesToRadians(180));

where DegreesToRadians is:

#define DegreesToRadians(d) ((d) * M_PI / 180.0)

To change the progress value, use positive numbers.

A simpler version is to flip it horizontally.

progressView.transform = CGAffineTransformMakeScale(-1.0f, 1.0f);

In iOS 9+, you can use semanticContentAttribute:

progressView.semanticContentAttribute = .forceRightToLeft

You can rotate the view by 180°:

progressView.transform = CGAffineTransformMakeRotation(-M_PI);

Swift answer:

progressView.transform = CGAffineTransform(rotationAngle: .pi)

In iOS 7 with storyboards, you can set the Progress Tint to the Track Tint and vice versa, then subtract the regular value from one and set that to the current progress. Probably better to do it the other (rotation) way, but I thought I would throw this out there.

Swift 5 Version

progressView.transform = CGAffineTransform(scaleX: -1.0, y: 1.0)