本文实例介绍了iOS实现左右拖动抽屉效果，具体内容如下

利用了触摸事件滑动 touchesMoved: 来触发左右视图的出现和消失 利用loadView方法中添加view 在self.view载入前就把 左右中View都设置好frame 每一个方法都由单独的功能。

#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

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