UIPanGestureRecognizer 滑动手势，侧边vi

#pragma mark -- 筛选 分类
- (void)clickFilterType {
    
    if (!_backView) {
        // 背景view
        _backView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, ScreenWidth, ScreenHeight)];
        _backView.backgroundColor = RGBA(0, 0, 0, 0.3);
        [self.view addSubview:self.backView];
    }
    
    if (!_filterBackView) {
        _filterBackView = [[VideoFilterBackView alloc] initWithFrame:CGRectMake(0, 0, ScreenWidth, ScreenHeight)];
        _filterBackView.backgroundColor = [UIColor clearColor];
        [self.backView addSubview:self.filterBackView];
        
        // 平移手势
        UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panAction:)];
        [self.filterBackView addGestureRecognizer:pan];
        
    }
}

- (void)panAction:(UIPanGestureRecognizer *)panGesture {
    
    _canLeft = YES;
    _canRight = YES;
    
//    panGesture = (UIPanGestureRecognizer *)self.filterBackView;
    
    // 获取平移手势移动后, 在相对坐标中的偏移量
    CGPoint transP = [panGesture translationInView:panGesture.view];
    // 偏移的速度
    CGPoint velocity = [panGesture velocityInView:panGesture.view];
    
    // 禁止左滑的情况（在最左边时）
    if (panGesture.view.frame.origin.x <= 0 && transP.x <= 0) {
        _canLeft = NO;
    }
    
    // 禁止右滑的情况（在最右边时）
    if (panGesture.view.frame.origin.x >= ScreenWidth && transP.x >= 0) {
        _canRight = NO;
    }
    
    // view滑动的条件
    if (_canLeft && _canRight && panGesture.view.frame.origin.x >= 0 && panGesture.view.frame.origin.x <= ScreenWidth) {
        
        // 移动
        panGesture.view.frame = CGRectMake( transP.x + panGesture.view.frame.origin.x, 0, ScreenWidth, ScreenHeight);
        
    }
    
    
    
//    self.filterBackView.frame = CGRectMake( transP.x + self.filterBackView.frame.origin.x, 0, ScreenWidth, ScreenHeight);
    // 每次都需要复位
    [panGesture setTranslation:CGPointZero inView:panGesture.view];
    
    // 松开手指时判断滑动趋势让其归位
    if (panGesture.state == UIGestureRecognizerStateEnded) {
        if (panGesture.view.frame.origin.x < ScreenWidth/2) { // 滑到一半位置
//            panGesture.view.frame.origin.x = 0;
            panGesture.view.frame = CGRectMake( 0, 0, ScreenWidth, ScreenHeight);
        } else if (panGesture.view.frame.origin.x > ScreenWidth/2) {
//            panGesture.view.frame.origin.x == ScreenWidth;
            panGesture.view.frame = CGRectMake(ScreenWidth, 0, ScreenWidth, ScreenHeight);
            
            // 右滑，隐藏
            [self.filterBackView removeFromSuperview];
            self.filterBackView = nil;
            
            [self.backView removeFromSuperview];
            self.backView = nil;
        }
    }
}