iOS实现左右拖动抽屉效果

#import "DarwViewController.h"
@interface DarwViewController ()
@property (nonatomic, weak) UIView *leftView;
@property (nonatomic, weak) UIView *rightView;
@property (nonatomic, weak) UIView *mainView;
/**
 * 动画是否进行
 */
@property (nonatomic ,assign) BOOL animating;
 
@end
 
@implementation DarwViewController
- (void)viewDidLoad {
  [super viewDidLoad];
}
 
 
-(void)loadView
{
  self.view = [[UIView alloc]initWithFrame:[UIScreen mainScreen].bounds];
  //左边view
  UIView *leftView = [[UIView alloc]initWithFrame:self.view.frame];
  [self.view addSubview:leftView];
  leftView.backgroundColor= [UIColor redColor];
  self.leftView = leftView;
   
  //右边View
  UIView *rightView = [[UIView alloc]initWithFrame:self.view.frame];
  [self.view addSubview:rightView];
  rightView.backgroundColor= [UIColor blueColor];
  self.rightView = rightView;
   
  //主页面
  UIView *mainView = [[UIView alloc]initWithFrame:self.view.frame];
  [self.view addSubview:mainView];
  mainView.backgroundColor= [UIColor yellowColor];
  self.mainView = mainView;
   
   
  //KVO监听
  [self.mainView addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionNew context:nil];
}
/**
 * KVO回调方法 当mainView Frame值改变时触发
 *
 * @param keyPath <#keyPath description#>
 * @param object <#object description#>
 * @param change <#change description#>
 * @param context <#context description#>
 */
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
  if (self.animating) return; //如果mainView正在动画 就不执行
  if (self.mainView.frame.origin.x > 0 )
  {
    //X > 0 就隐藏右边View 显示左边View
    self.rightView.hidden = YES;
    self.leftView.hidden = NO;
  }
  else if (self.mainView.frame.origin.x < 0)
  {
    //X < 0 就隐藏左边View 显示右边VIew
    self.leftView.hidden = YES;
    self.rightView.hidden = NO;
  }
}
#pragma mark -- 触摸事件
-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  //获得触摸对象
  UITouch *touch = [touches anyObject];
   
  //获得当前触摸点
  CGPoint currentPoint = [touch locationInView:self.view];
  //获得上一个触摸点
  CGPoint previousPoint = [touch previousLocationInView:self.view];
   
  //计算x方向的偏移量
  CGFloat offsetX = currentPoint.x - previousPoint.x;
//  根据x的偏移量计算y的偏移量
  self.mainView.frame = [self rectWithOffsetX:offsetX];
   
}
#define screenW [UIScreen mainScreen].bounds.size.width
#define screenH [UIScreen mainScreen].bounds.size.height
/**
 * 计算主视图的frame
 *
 * @param offsetX x的偏移量
 *
 * @return 偏移后新的frame
 */
- (CGRect ) rectWithOffsetX:(CGFloat )offsetX
{
  //Y轴的偏移量
  CGFloat offsetY = (screenH *1/5) * (offsetX/screenW);
   
  //比例 ：（用于宽高的缩放）
  CGFloat scale = (screenH - offsetY *2) / screenH;
  if (self.mainView.frame.origin.x < 0 )
  {
    //如果x是负数 及左边View要显示
    //比例就要设为比1小
    scale = 2 - scale;
  }
  //获取当前mainView的frame
  CGRect frame = self.mainView.frame;
   
  //重新设置mainView的frame值
  frame.size.width = frame.size.width *scale >screenW ? screenW : frame.size.width *scale;
   
  frame.size.height = frame.size.height *scale >screenH ? screenH :frame.size.height *scale;
   
  frame.origin.x += offsetX;
  frame.origin.y =(screenH - frame.size.height)*0.5;
  //返回偏移后新的frame
  return frame;
}
#define maxRightX (screenW *0.8)
#define maxLeftX (-screenW *0.6)
-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
  CGFloat targetX = 0;
  //如果松手的那一下 当前mainVIew的x大于屏幕的一半
  if (self.mainView.frame.origin.x > screenW * 0.5)
  {
    //向右边定位
    targetX = maxRightX;
  }
  //如果松手的那一下 当前mainVIew的最大X值小于屏幕的一半
  else if (CGRectGetMaxX(self.mainView.frame) < screenW *0.5)
  {
    //向左边定位
    targetX = maxLeftX;
  }
   
  //计算偏移量
  CGFloat offsetX = targetX -self.mainView.frame.origin.x;
   
  self.animating = YES;
   
  [UIView animateWithDuration:0.4 animations:^{
    if (targetX == 0)
    {
      //如果targetX==0 复位
      self.mainView.frame = self.view.frame;
    }
    else
    {
      //如果targetX != 0 那就到指定位置
      self.mainView.frame = [self rectWithOffsetX:offsetX];
    }
  } completion:^(BOOL finished) {
    self.animating = NO;
  }];
     
}
@end