抽屉效果

所谓抽屉效果就是三个视图，向右拖拽显示左边的视图，向左拖拽显示右边的视图，当拖拽大于屏幕的一半时最上面的视图会自动定位到一边，当点击左边或右边视图时会最上面视图会自动复位。

效果如图：三个视图（左边：浅灰色视图、右边：品红视图、主视图：黑色视图）

封装代码

DrawerViewController

#import 
@interface DrawerViewController : UIViewController

@property (weak, nonatomic, readonly) UIView *leftView;
@property (weak, nonatomic, readonly) UIView *rightView;
@property (weak, nonatomic, readonly) UIView *mainView;

@end

// -------------------------------------------------------
#import "DrawerViewController.h"

#define ScreenWidth [UIScreen mainScreen].bounds.size.width
#define ScreenHeight [UIScreen mainScreen].bounds.size.height
#define MaxOffsetY 100
#define MaxOffsetX ([UIScreen mainScreen].bounds.size.width - 100)

@implementation DrawerViewController
- (void)viewDidLoad {
 [super viewDidLoad];

 // 1. 初始化视图
 [self setup];

 // 2. 给mainView添加拖动手势
 UIPanGestureRecognizer *panGestureRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panGesture:)];
 [self.mainView addGestureRecognizer:panGestureRecognizer];

 // 3. 给self.view添加一个单击手势
 UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapGesture:)];
 [self.view addGestureRecognizer:tap];
}

- (void)tapGesture:(UITapGestureRecognizer *)tap {
 // mainView复位
 [UIView animateWithDuration:0.2 animations:^{
  self.mainView.frame = self.view.bounds;
 }];
}

- (void)panGesture:(UIPanGestureRecognizer *)pan {
 CGPoint offsetPoint = [pan translationInView:self.view];
 self.mainView.frame = [self frameWithOffset:offsetPoint.x];

 if (self.mainView.frame.origin.x > 0) {
  // → 右移(显示leftView)
  self.rightView.hidden = YES;
 } else if (self.mainView.frame.origin.x < 0) {
  // ← 左移(显示rightView)
  self.rightView.hidden = NO;
 }

 // 如果拖拽结束，自动定位
 CGFloat targetOffsetX = 0;
 if (pan.state == UIGestureRecognizerStateEnded) {
  if (self.mainView.frame.origin.x >= ScreenWidth * 0.5) { // 右侧
   targetOffsetX = MaxOffsetX;
  } else if (CGRectGetMaxX(self.mainView.frame) < ScreenWidth * 0.5){ // 左侧
   targetOffsetX = -MaxOffsetX;
  }

  // 计算出当前位置距离目标位置所需要的偏移距离
  CGFloat offsetX = targetOffsetX - self.mainView.frame.origin.x;

  // 滑动不到屏幕一般时仍然显示mainView(self.view.bounds) 否则自动定位到左侧或右侧
  CGRect mainFrame = targetOffsetX == 0 ? self.view.bounds : [self frameWithOffset:offsetX];
  [UIView animateWithDuration:0.2 animations:^{
   self.mainView.frame = mainFrame;
  }];
 }

 [pan setTranslation:CGPointZero inView:self.view];
}

- (CGRect)frameWithOffset:(CGFloat)offsetX {
 CGRect newFrame = self.mainView.frame;
 newFrame.origin.x += offsetX;  // x


 CGFloat offsetY = self.mainView.frame.origin.x * MaxOffsetY / ScreenWidth;
 newFrame.origin.y = fabs(offsetY); // y

 CGFloat offsetHeight = ScreenHeight - (newFrame.origin.y * 2);
 newFrame.size.height = offsetHeight; // height

 return newFrame;
}

- (void)setup {
 UIView *leftView = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
 //leftView.backgroundColor = [UIColor lightGrayColor];
 _leftView = leftView;
 [self.view addSubview:leftView];

 UIView *rightView = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
 //rightView.backgroundColor = [UIColor magentaColor];
 _rightView = rightView;
 [self.view addSubview:rightView];

 UIView *mainView = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
 //mainView.backgroundColor = [UIColor blackColor];
 _mainView = mainView;
 [self.view addSubview:mainView];
}

@end

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