collectionView的联动效果

Snip20160726_1.png

这次的电影项目，很多地方都用到了collectionView，像图片的显示，相册的显示等等。这里我要说的是图片的联动，item的位置计算，蒙版的添加。强调下item的计算需要关闭自动分页。

1、collectionView的创建，minimumLineSpacing这个属性如果是垂直cell的话，那么cell的之间的行间距用这个，如果是水平cell的话，那么列间距用这个。数据的显示都是套路，创建模型，自定义cell，设置模型属性，从控制器注册cell并传值。

    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    
    UICollectionView *posterView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 64, WScreen, self.height) collectionViewLayout:layout];
    self.posterView = posterView;
    layout.itemSize = CGSizeMake(WScreen-100, self.height-100);
    layout.minimumLineSpacing = 50;
    // 水平滑动
    layout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    posterView.backgroundColor = [UIColor orangeColor];
    posterView.hidden = NO;
    // 分页效果，因为自动计算，所有关闭
    // posterView.pagingEnabled = YES;
    posterView.dataSource = self;
    posterView.delegate = self;
    // 水平挪动
    posterView.showsHorizontalScrollIndicator = NO;
    
    [self addSubview:posterView];
    
    // 注册
    [posterView registerClass:[WXPosterCell class] forCellWithReuseIdentifier:@"cell"];

2、item的计算，用到的就是这个方法，主要是根据偏移量计算第几页

// 做这个功能一定要关闭分页效果
- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset {
    
    // 1.根据偏移量来计算第几个item
    CGFloat offSetX = targetContentOffset->x;
    
    // 2.item的宽度
    CGFloat itemWidth = WScreen - 100;
    
    // 3.页码的宽度
    NSInteger pageWith = itemWidth + 50;
    
    // 4.根据偏移量计算第几页
    NSInteger pageNum = (offSetX + pageWith/2) / pageWith;
    
    // 5.根据第几个item改变偏移量
    targetContentOffset->x = pageWith * pageNum;
    
    self.smallView.posterIndex = pageNum;
}

3、联动效果是使用观察者实现

#pragma mark - 观察者
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    
    NSInteger index = [[change objectForKey:@"new"]integerValue];
    
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:index inSection:0];
    
    
    [UIView animateWithDuration:0.35 animations:^{
        
        [self.posterView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];
    }];
    
}

4、下拉菜单的实现

// 创建按钮
    UIButton *button = [[UIButton alloc] init];
    self.btn = button;
    button.frame = CGRectMake((self.headView.width - 20)/2, self.headView.height - 20, 20, 20);
    [button setImage:[UIImage imageNamed:@"down_home"] forState:UIControlStateNormal];
    [button setImage:[UIImage imageNamed:@"up_home"] forState:UIControlStateSelected];
    [button addTarget:self action:@selector(selectedAction:) forControlEvents:UIControlEventTouchUpInside];
    [self.headView addSubview:button];

#pragma mark - 显示或隐藏
- (void)shouHead {
    
    [UIView animateWithDuration:0.35 animations:^{
        
        self.headView.transform = CGAffineTransformMakeTranslation(0, self.headView.height-42);
        self.hud.hidden = NO;
        
    }];
}

- (void)hiddenHead {
    
    [UIView animateWithDuration:0.35 animations:^{
        
        self.headView.transform = CGAffineTransformIdentity;
        self.hud.hidden = YES;
        
    }];
}

- (void)selectedAction:(UIButton *)btn {

    if (!btn.selected) {
        
        [self shouHead];
        
    } else {
        
        [self hiddenHead];
    }
    
    btn.selected = !btn.selected;
}

项目请看https://github.com/liangxingyan/Movie.git