高性能异构滚动视图

参考文档
链接文章是天猫开源的一个异构滚动视图，并在天猫苹果端实现，其涉及高效复用，学习后简单码一下。

异构滚动视图是相对于TableView的同构滚动视图而言。普通ScrollView视图较少时不用考虑复用题，但当数量不断增加后复用就显得很必要。

STEP1.

    TMMuiLazyScrollView *scrollview = [[TMMuiLazyScrollView alloc]init];
    scrollview.frame = self.view.bounds;
    //设置contentSize
    scrollview.contentSize = CGSizeMake(CGRectGetWidth(self.view.bounds), 1230);
    scrollview.dataSource = self;
    [self.view addSubview:scrollview];
    
    
    //Here is frame array for test.
    //LazyScrollView must know every rect before rending.
    //必须先设置每个Item相对于滚动视图的绝对坐标
    rectArray  = [[NSMutableArray alloc] init];
    
    //单列Item
    //Create a single column layout with 5 elements;
    for (int i = 0; i < 5 ; i++) {
        [rectArray addObject:[NSValue valueWithCGRect:CGRectMake(10, i *80 + 2 , self.view.bounds.size.width-20, 80-2)]];
    }
    //双列item
    //Create a double column layout with 10 elements;
    for (int i = 0; i < 10 ; i++) {
        [rectArray addObject:[NSValue valueWithCGRect:CGRectMake((i%2)*self.view.bounds.size.width/2 + 3, 410 + i/2 *80 + 2 , self.view.bounds.size.width/2 -3, 80 - 2)]];
    }
    //三列item
    //Create a trible column layout with 15 elements;
    for (int i = 0; i < 15 ; i++) {
        [rectArray addObject:[NSValue valueWithCGRect:CGRectMake((i%3)*self.view.bounds.size.width/3 + 1, 820 + i/3 *80 + 2 , self.view.bounds.size.width/3 -3, 80 - 2)]];
    }
    
    //STEP 3 reload LazyScrollView
    //相当于再走一遍代理方法
    [scrollview reloadData];

STEP2.

//第二步 实现代理方法
// implement datasource delegate.
- (NSUInteger)numberOfItemInScrollView:(TMMuiLazyScrollView *)scrollView
{
    return rectArray.count;
}
//根据index返回rectModel
- (TMMuiRectModel *)scrollView:(TMMuiLazyScrollView *)scrollView rectModelAtIndex:(NSUInteger)index
{
    CGRect rect = [(NSValue *)[rectArray objectAtIndex:index]CGRectValue];
    TMMuiRectModel *rectModel = [[TMMuiRectModel alloc]init];
    
    //两个属性，一个相对于异构视图的绝对位置，一个唯一ID
    rectModel.absoluteRect = rect;
    rectModel.muiID = [NSString stringWithFormat:@"%ld",index];
    return rectModel;
}
//根据MuiID返回对应的view,view与rectModel数量一致
- (UIView *)scrollView:(TMMuiLazyScrollView *)scrollView itemByMuiID:(NSString *)muiID
{
    //Find view that is reuseable first.
    //首先取出复用的Item
    LazyScrollViewCustomView *label = (LazyScrollViewCustomView *)[scrollView dequeueReusableItemWithIdentifier:@"testView"];
    
    //索引用的标识，在异构视图中唯一
    NSInteger index = [muiID integerValue];
    NSLog(@"========%ld",index);
    //如果不存在则新建
    if (!label)
    {
        label = [[LazyScrollViewCustomView alloc]initWithFrame:[(NSValue *)[rectArray objectAtIndex:index] CGRectValue]];
        label.textAlignment = NSTextAlignmentCenter;
        label.reuseIdentifier = @"testView"; //重用ID
    }
    
    label.frame = [(NSValue *)[rectArray objectAtIndex:index]CGRectValue];
    label.text = [NSString stringWithFormat:@"%lu",(unsigned long)index];
    label.backgroundColor = [self randomColor];
    label.userInteractionEnabled = YES;
    
    [scrollView addSubview:label];

    [label addGestureRecognizer:[[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(click:)]];
    
    return label;
}

PS: GitHub 上提供的这个Demo更多地展示的是高效复用，也许是因为很少有相应的需求场景，感觉灵性有些欠缺，后期需要不断尝试实践。