title: Changing the speed of a CAKeyframeAnimation mid-animation in iOS
body: <p>I am trying to allow the user to change the speed of my animation. I am making a CAKeyframeAnimation with a bezier path, and I can get it to display and run correctly.
  I try to change the speed by creating a new animation path with a different duration. The planes go back to the beginning (which I haven't tried to fix yet) and do speed up. The path that they are being drawn on goes away at the time it would have had the animation never changed speeds. When the planes finish, another appears at the point at which the animation was paused in the first place. I have no idea what I'm doing wrong. My question is similar to this one <a href="https://stackoverflow.com/questions/13286702/modifying-dynamically-the-duration-of-cakeyframeanimation">modifying dynamically the duration of CAKeyframeAnimation</a>, but I don't understand what the OP said about finally using blocks.</p>
  
  <pre><code>//The first two methods are in a class subclassing UIView
  /** Pause each plane's animation */
  - (void)pauseAnimation
  {    
      CFTimeInterval pausedTime = [[self layer] convertTime:CACurrentMediaTime() fromLayer:nil];
      [self layer].speed = 0.0;
      [self layer].timeOffset = pausedTime;
  }
  
  /** Resume each plane's animation */
  - (void)resumeAnimation
  {
      CFTimeInterval pausedTime = [[self layer] timeOffset];
      [self layer].speed = 1.0;
      [self layer].timeOffset = 0.0;
      CFTimeInterval timeSincePause = [[self layer] convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
  
      for(SEPlane *plane in planes){
          plane.planeAnimationPath.speedMultiplier = 5;
          [plane.planeAnimationPath beginAnimation:self];
      }
      //[self layer].beginTime = timeSincePause;
  }
  
  //This method is in the class of planeAnimationPath
  /** Begin animating plane along given path */
  - (void)beginAnimation:(UIView *) view
  {
      planeAnimation = nil;
      // Create animation layer for animating plane
      planeAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];    
      planeAnimation.path = [bezierPath CGPath];
      planeAnimation.duration = approximateLength/(ANIMATION_SPEED * self.speedMultiplier);
      planeAnimation.calculationMode = kCAAnimationPaced;
      planeAnimation.fillMode = kCAFillModeForwards;
      planeAnimation.rotationMode = kCAAnimationRotateAuto;
      planeAnimation.removedOnCompletion = YES;
      [planeAnimation setDelegate:self];    
  
      // Add animation to image-layer
      [imageLayer addAnimation:planeAnimation forKey:animationKey];
  
      // Add image-layer to view
      [[view layer] addSublayer:imageLayer];
  }
  </code></pre>