material-components_material-components-ios/components/HeaderStackView/src/MDCHeaderStackView.m

// Copyright 2016-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 <CoreGraphics/CoreGraphics.h>

#import "MDCHeaderStackView.h"

@implementation MDCHeaderStackView

- (CGSize)sizeThatFits:(CGSize)size {
  if (_bottomBar) {
    size.height = [_bottomBar sizeThatFits:size].height;
  } else {
    size.height = [_topBar sizeThatFits:size].height;
  }
  return size;
}

- (void)layoutSubviews {
  [super layoutSubviews];

  CGSize boundsSize = self.bounds.size;

  CGSize bottomBarSize = [_bottomBar sizeThatFits:boundsSize];
  CGFloat remainingHeight = boundsSize.height - bottomBarSize.height;
  CGSize topBarSize = [_topBar sizeThatFits:CGSizeMake(boundsSize.width, remainingHeight)];
  remainingHeight -= topBarSize.height;

  CGRect topBarFrame = CGRectMake(0, 0, topBarSize.width, topBarSize.height);
  CGRect bottomBarFrame = CGRectMake(0, 0, bottomBarSize.width, bottomBarSize.height);

  if (remainingHeight > 0) {
    // Expand the top bar to fill the remaining height.
    topBarFrame.size.height += remainingHeight;

  } else if (remainingHeight < 0) {
    // Negative value causes the top bar to slide up and away.
    topBarFrame.origin.y += remainingHeight;
  }
  bottomBarFrame.origin.y = CGRectGetMaxY(topBarFrame);

  _topBar.frame = topBarFrame;
  _bottomBar.frame = bottomBarFrame;
}

#pragma mark - Public

- (void)setTopBar:(UIView *)topBar {
  if (_topBar == topBar) {
    return;
  }

  [_topBar removeFromSuperview];

  _topBar = topBar;

  [self addSubview:_topBar];
  [self setNeedsLayout];
}

- (void)setBottomBar:(UIView *)bottomBar {
  if (_bottomBar == bottomBar) {
    return;
  }

  [_bottomBar removeFromSuperview];

  _bottomBar = bottomBar;

  [self addSubview:_bottomBar];
  [self setNeedsLayout];
}

@end