Animating UILabel origin and width

Two approaches. Assuming your 'newFrame' is correct (it contains a center):

[UIView animateWithDuration:0.5 animations:^{       
     label.frame=newFrame;
    }];

and if they it is not correct this will work:

[UIView animateWithDuration:0.5 animations:^{        
     label.frame=CGRectMake(label.frame.origin.x-button.frame.size.width,
                            label.frame.origin.y,
                            label.frame.size.width+button.frame.size.width,
                            label.frame.size.height);
    }];

I wish it were that simple ... I've tried code like you suggest. I do get an animation but not the way I need it.

With both of your suggestions the label appears to snap to the final size and then go to its final location.

That's not the effect I need. I for the label to stay on its right margin and change it's origin to compensate for teh new size.

I wrote a standalone test app to troubleshoot this. Here's the complete in Swift using Xcode 7.3.

import UIKit
class ViewController: UIViewController {

  var toggleState = false
  var originalFrame: CGRect = CGRectZero

  let sizeChange: CGFloat = 50

  var testLabel = UILabel()

  override func viewDidLoad() {
    super.viewDidLoad()
  
    testLabel = UILabel(frame: CGRectMake(70, 40, 200, 50))
    testLabel.center = CGPointMake(160, 284)
    testLabel.textAlignment = NSTextAlignment.Center
    testLabel.text = "I'am a test label"
    testLabel.backgroundColor = UIColor.yellowColor()
    self.view.addSubview(testLabel)
    originalFrame = testLabel.frame
    let button   = UIButton(type: UIButtonType.System) as UIButton
    button.frame = CGRectMake(20, 20, 100, 50)
    button.backgroundColor = UIColor.greenColor()
    button.setTitle("Toggle Label", forState: UIControlState.Normal)
  
    button.addTarget(self, action: #selector(ViewController.buttonAction(_:)), forControlEvents: UIControlEvents.TouchUpInside)
  
    self.view.addSubview(button)
  }
  func buttonAction(sender:UIButton!) {
    print("Old Frame: \(testLabel.frame) Center: \(testLabel.center)")
    UIView.animateWithDuration(0.5, animations: {
      self.testLabel.frame = CGRect(
        x: self.toggleState ? self.originalFrame.origin.x : (self.originalFrame.origin.x - self.sizeChange),
        y: self.testLabel.frame.origin.y,
        width: (self.toggleState ? self.originalFrame.size.width : (self.originalFrame.size.width + self.sizeChange)),
        height: self.testLabel.frame.size.height)
      }, completion: { finished in
        print("New Frame: \(self.testLabel.frame) Center: \(self.testLabel.center)")
    })
    toggleState = !toggleState
  }
}

Just touch the toggle label button. You'll see that the label animates as I describe.

My code works for me for some animations but I see it fails for others! It is easier to see what works by setting the duration to 5 seconds. In my case I can get your label to grow smoothly and expand to the left but then when I want it to shrink to the right it snaps to a smaller size and moves right.

I have no idea what is wrong. Perhaps it is a bug. Here is what I had been doing for animations:

  // create this dictionary of variables:
    NSMutableDictionary *theVariables=[NSMutableDictionary dictionaryWithObjectsAndKeys:
              testLabel@"TheView",   //  the UIView object you want to animate
             [NSValue valueWithCGRect:CGRectMake(x,y,width,height),@"TheFinalFrame", // the frame to move the object to
             [NSNumber numberWithFloat:0.50],@"TheDuration", nil]; // the duration in seconds
    // then call:
    [self smoothMoveWithVariables:theVariables];
-(void)smoothMoveWithVariables:(NSMutableDictionary *)theVariables{
    UIView *theView=[theVariables objectForKey:@"TheView"];
    float theDurationRemaining=[[theVariables objectForKey:@"TheDuration"] floatValue];
    CGRect theFinalFrame=[[theVariables objectForKey:@"TheFinalFrame"] CGRectValue];
    float framesPerSecond=30; /
    int framesRemaining=theDurationRemaining*framesPerSecond;
    if(framesRemaining>0){
        theView.frame=CGRectMake(
                                 theView.frame.origin.x+(theFinalFrame.origin.x - theView.frame.origin.x)/framesRemaining,
                                 theView.frame.origin.y+(theFinalFrame.origin.y - theView.frame.origin.y)/framesRemaining,
                                 theView.frame.size.width+(theFinalFrame.size.width - theView.frame.size.width)/framesRemaining,
                                 theView.frame.size.height+(theFinalFrame.size.height - theView.frame.size.height)/framesRemaining);
        theDurationRemaining=theDurationRemaining-1/framesPerSecond;
        if(theDurationRemaining>1/framesPerSecond){
            [theVariables setObject:[NSNumber numberWithFloat:theDurationRemaining] forKey:@"TheDuration"];
            [self performSelector:@selector(smoothMoveWithVariables:) withObject:theVariables afterDelay:0.033f];  /
        }
    }
}

You may want to be a bit careful. Although this method can be called by overlapping labels, if you deallocate the class before it completes then it could crash. Before deallocating the class call [NSObject cancelPreviousPerformRequestsWithTarget:self];