Question

I have a progress view that I’m trying to animate the change in progress. How do you go about doing that? Below is the code to draw the progress.

Thanks in advance

- (void)drawRect:(CGRect)rect {
    // Drawing code.
    CGContextRef context = UIGraphicsGetCurrentContext();

    // draw the background
    CGContextSaveGState(context);
    UIBezierPath *outerPath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:0];
    [outerPath addClip];

    CGPoint backgroundStartPoint = CGPointMake(0.0f, 0.0f);
    CGPoint backgroundEndPoint = CGPointMake(0.0f, CGRectGetHeight(rect));
    CGContextDrawLinearGradient(context, _backgroundGradient, backgroundStartPoint, backgroundEndPoint, 0);

    CGContextRestoreGState(context);

    // draw the progress
    CGContextSaveGState(context);
    UIBezierPath *innerPath = [UIBezierPath bezierPathWithRoundedRect:CGRectInset(rect, 1.0f, 1.0f) cornerRadius: 0];
    [innerPath addClip];

    [_glossTintColor setFill];
    CGRect progressRect = CGRectMake(0, 0, CGRectGetWidth(rect)*_progress, CGRectGetHeight(rect));
    CGContextFillRect(context, progressRect);

    CGContextRestoreGState(context);
}

Answer 1

Whenever the progress changes, trigger a redraw using [view setNeedsDisplay];

See the UIView reference on setNeedsDisplay.

For example, lets say that custom view you have created has a property called progress, the instance variable is called _progress. Lets also suppose that property gets updated by some event/timer/additional thread.

- (void)setProgress:(float)progress
{
    _progress = progress;
    [self setNeedsDisplay];
}

That overrides the original setter and adds the functionality mentioned above.