UIScrollView优于UITableView和UICollectionView的优势

Question

I'm working on a MAC tool where you can see the current viewcontroller UIElements hierarchy of an iOS app. I use to test it with so many third party apps. As per my knowledge to list something in horizontal or vertical most of the time developer use UITableView or UICollectionView .

While testing some of the standard apps (especially e-commerce) are using UIScrollView with UIView as subview and added gesture on it. What i'm trying to understand is, why these apps are not using tableview or collection to list something? and what is the reason behind this?

Answer 1

This are some of things I always prefer UITableView and UICollectionView.

1. One of most advantage of UITableView and UICollectionView is reusability .
2. When comes to autolayout its easy to handle UITableView and UICollectionView over UIScrollView
3. Indexing of views
4. Delegate methods support
5. Reload(Update) Views its easy compare to UIScrollView

One thing I miss is Paging in UITableView and UICollectionView as its so smooth in UIScrollView

Answer 2

(1) Advantage of using UITableView or UICollectionView against UIScrollView is for memory.

For example if you have 100 items then you have to keep adding below in UIScrollView, so it 100 items data will be in memory.

In UITableView or UIcollectionView there is dequeueReusableCellWithIdentifier that keeps only those items in memory which are visible. When you scroll up / down though items are not visible will be in memory.

(2) Delegate methods - NoOfSections, NoOfRows, DidSelectedRow etc - Though things are not available in UIScrollView.So you have to manage through coding.

Answer 3

UICollectionView Class :-

The UICollectionView class manages an ordered collection of data items and presents them using customizable layouts. Collection views provide the same general function as table views except that a collection view is able to support more than just single-column layouts. Collection views support customizable layouts that can be used to implement multi-column grids, tiled layouts, circular layouts, and many more. You can even change the layout of a collection view dynamically if you want.

UITableView Class:-

A table view displays a list of items in a single column. UITableView is a subclass of UIScrollView, which allows users to scroll through the table, although UITableView allows vertical scrolling only. The cells comprising the individual items of the table are UITableViewCell objects; UITableView uses these objects to draw the visible rows of the table. Cells have content—titles and images—and can have, near the right edge, accessory views. Standard accessory views are disclosure indicators or detail disclosure buttons; the former leads to the next level in a data hierarchy and the latter leads to a detailed view of a selected item. Accessory views can also be framework controls, such as switches and sliders, or can be custom views. Table views can enter an editing mode where users can insert, delete, and reorder rows of the table.

People mainly use the UICollectionview for creating types of UIs with multiple images shown in a grid. This would have complex logic using UITableView, but with UICollectionview , it would be easy.

Answer 4

UITableView has many advantages over UIScrollView like:

• When using auto layout, UITableView is more reusable.
• List item

Memory management is better in case of UITableView.

Answer 5

One advantage of UIScrollView over UITableView/UICollectionView/AutoLayout is smooth scroll performance.

Recently, I needed to reimplement some old news app which used UIScrollView to display news content. App would create all views and add them to UIScrollView. That would consume ca 15-20 MB of RAM memory.

The new design I had to implement was more complex, but could be achieved either via UIScrollView or UITableView and UICollectionView combination. I went with UITableView & UICollectionView and Auto Layout. After finishing implementation, performance was TERRIBLE. Previous UIScrollView implementation was perfect 60fps on iPhone 4S. With the new implementation I would get dropped frames even on iPhone 6S. I optimized images so that they're resized on background so that there are no misaligned images and I also minimized blended layers passes. That helped a bit, but still far from perfect.

I ended up dropping AutoLayout in many places and preloading all UITableView cells and keeping them in an NSArray so cells can be returned immediately without configuring (since that takes time). With this of course, table view cell reusability went down the toilet, but scroll performance improved quite a bit even on iPhone 4S.

Conclusion: sometimes, UIScrollView and manual frame calculation is worth the effort if your whole view is not too large so that it can fit into memory relatevly easily. Often, UITableView & UICollectionView & Auto Layout can prove expensive in terms of dropped frames while scrolling. End users won't care how you implemented it, but they will complain about app not being smooth.

Of course, rarely do you ever need this. ALWAYS stick first to UITableView & AutoLayout (or UICollectionView & AutoLayout if needed) since they make life easier for many reasons (easy various screen sizes support including rotations), but do keep in mind that there is a UIScrollView should a black day come and a need arise.