components/private/TextControlsPrivate/src/Shared/MDCTextControlLabelAnimation.m

// Copyright 2019-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#import <QuartzCore/QuartzCore.h>

#import "MDCTextControlLabelAnimation.h"

#import "MDCTextControlLabelSupport.h"

@implementation MDCTextControlLabelAnimation

+ (void)animateLabel:(nonnull UILabel *)label
                       state:(MDCTextControlLabelPosition)labelPosition
            normalLabelFrame:(CGRect)normalLabelFrame
          floatingLabelFrame:(CGRect)floatingLabelFrame
                  normalFont:(nonnull UIFont *)normalFont
                floatingFont:(nonnull UIFont *)floatingFont
    labelTruncationIsPresent:(BOOL)labelTruncationIsPresent
           animationDuration:(NSTimeInterval)animationDuration
                  completion:(void (^__nullable)(BOOL))completion {
  BOOL isAnimationInProgress = label.layer.animationKeys.count > 0;
  if (isAnimationInProgress) {
    if (completion) {
      completion(NO);
    }
    return;
  }

  UIFont *targetFont;
  CGRect targetFrame;
  if (labelPosition == MDCTextControlLabelPositionFloating) {
    targetFont = floatingFont;
    targetFrame = floatingLabelFrame;
  } else {
    targetFont = normalFont;
    targetFrame = normalLabelFrame;
  }

  CGRect currentFrame = label.frame;
  CGAffineTransform transformNeededToMakeViewWithCurrentFrameLookLikeItHasTargetFrame =
      [self transformFromRect:currentFrame toRect:targetFrame];

  BOOL willChangeFrame = !CGRectEqualToRect(currentFrame, targetFrame);
  BOOL currentFrameIsCGRectZero = CGRectEqualToRect(currentFrame, CGRectZero);
  BOOL isNormalTransition = willChangeFrame && !currentFrameIsCGRectZero;
  BOOL nonZeroDuration = animationDuration > 0;
  BOOL shouldPerformAnimation = nonZeroDuration && isNormalTransition && !labelTruncationIsPresent;

  void (^completionBlock)(BOOL finished) = ^void(BOOL finished) {
    label.transform = CGAffineTransformIdentity;
    label.frame = targetFrame;
    label.font = targetFont;
    if (completion) {
      completion(YES);
    }
  };

  if (shouldPerformAnimation) {
    dispatch_async(dispatch_get_main_queue(), ^{
      CAMediaTimingFunction *timingFunction =
          [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
      [CATransaction begin];
      [CATransaction setAnimationTimingFunction:timingFunction];
      [UIView animateWithDuration:animationDuration
                            delay:0
                          options:0
                       animations:^{
                         label.transform =
                             transformNeededToMakeViewWithCurrentFrameLookLikeItHasTargetFrame;
                       }
                       completion:completionBlock];
      [CATransaction commit];
    });
  } else {
    completionBlock(YES);
  }
}

/**
 This helper method returns the transform that would need to be applied to a view with a frame of @c
 sourceRect in order for it to appear as though its frame was @c finalRect.
 */
+ (CGAffineTransform)transformFromRect:(CGRect)sourceRect toRect:(CGRect)finalRect {
  CGAffineTransform transform = CGAffineTransformIdentity;
  transform =
      CGAffineTransformTranslate(transform, -(CGRectGetMidX(sourceRect) - CGRectGetMidX(finalRect)),
                                 -(CGRectGetMidY(sourceRect) - CGRectGetMidY(finalRect)));
  transform = CGAffineTransformScale(transform, finalRect.size.width / sourceRect.size.width,
                                     finalRect.size.height / sourceRect.size.height);

  return transform;
}

@end