I am trying to figure out if there's a way to create something like a UICollectionView for an arbitrary and potentially infinite amount of UICollectionViewCells. I also want to be able to do fancy things with my own UICollectionViewLayout.
What I'm trying to do is create a dataSource that's a linked-list. So each element in the dataSource knows which element comes before and after it. I have no idea how big the list is. I don't care.
I've looked at the UITableView stuff and it needs to know how many elements are in it. I've looked at the UICollectionView stuff and it ALSO needs to know how many elements are in it. The UICollectionViewLayout needs to know how big the view needs to be (collectionViewContentSize). All of this is frustrating to me because I don't see why this much detail is needed.
For simplicities sake, lets assume that I only need to show ONE cell at a time. I don't see why I can't just tell the View that it's only 3-cells wide (always) and when you scroll to the left or right, pop the cell of the long side and put it on the short side? At no point will I need to be able to say "scroll to 5" I just want to be able to say "next, next, next" or "prev, prev, prev"
What's the best way to capture this behavior?
The best answer I can think of thus far is to basically do what I said w/ the "use three cells" thing. I could just have a CollectionView that is concerned with how to best lay out some n-cells (where n is 3, or 5, or 25, or somethign) and some other thing that is concerned with what to be putting in each cell and while the view is cycling between the same n cells, the data thing is pushing the appropriate data into them?
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I'm developing an Chat application where I have a UICollectionView to control the messages and I came to a situation I would like to confirm with you.
For exemple, let's say I have 60 items in this UICollectionView, but based on the size of the items and the scrolling options I set, only the last 10 items are visible on the screen, from 50 to 59.
Based on that, it seems I'm not able to get cellForItem at IndexPath 30, for example. Is that correct?
I would like to confirm that with you before creating a solution to go over the items that are already "on screen" and I need to check. Any ideas and solutions you have already implemented is appreciated.
Also, based on the information above if, for example, I need to move on item from index path 30 to 31, will I have problems if they are not "instantiated" in the screen?
Thanks in advance!
You seem to be mixing your model, controller, and view classes, which is a bad thing™ for exactly the reason you encounter here.
I take it you're trying to access data from the index 30 (basically) and say to yourself "Hey, I already added that in the 30th cell, so I will just use the collection view's method to get that cell and take it from there". That means, you basically ask a view for data.
That won't work, because, as others pointed out (but more indirectly), there are not 60 cells at all at any given moment. There's basically as many cells as fit on the screen, (plus perhaps one or a few "buffer" cells so rendering during scrolling works, I can't remember that atm). This is why cellForItem(at:) is nil for an IndexPath that refers to a cell not actually visible at the moment. Basically it works in a similar way to a table view. The collection view simply does not keep around stuff it doesn't need to render for memory reasons.
If you need anything from a cell (which is after all also a view) at this path, why don't you get it from whatever data object represents the contents of this cell? Usually that's the UICollectionViewDataSource.
That's how the paradigm is supposed to work: The UICollectionViewDataSource is responsible for keeping around any data your app may need at a given time (this may or may not reloading it or parts of it, your choice). The UICollectionView uses its collectionView(_:cellForItemAt:) method when a certain IndexPath becomes visible, but it throws that away again (or rather queues it again so your data source may dequeue it in collectionView(_:cellForItemAt:) and reuse it for another data set that becomes visible).
And btw, please don't use use the UICollectionViewDataSource's collectionView(_:cellForItemAt:) method to get the cell and then the data from there. This method is supposed to be called by the collection view and depending on how you reuse cells or create them, this might mess up the entire process. Or at the very least create view-related overhead. Instead, get the data in the same way your UICollectionViewDataSource would get in inside of the method. Wrap that in an additional method you rely on or the like. Or, even better, rely on the model object that the controller uses as well.
Edit in response to your comment:
No, I did not mean it's bad to use a UIViewController as a UICollectionViewDataSource for a UICollectionView. What I meant was that it's bad to use the UICollectionView to get data, because that's what the data source is for. In your question you were wondering why cellForItem(at:) gives nil. That method is defined on UICollectionView. You didn't mention your intention was to move items around (I'll explain in a second), so I assumed you were trying to get whatever data was in the cell (I know, "assume makes an ass out of u and me...", sorry :) ). This is not the way to go, as the UICollectionView is not meant to hold the data for you. Rather, that's your job, and you can use a UICollectionViewDataSource for that. This latter class (or rather protocol a class can adopt) is basically meant to offer an interface for UICollectionView to get the data. It needs that, because, as said, it doesn't keep all data around. It requests stuff it needs from the data source. The data source, on the other hand, can manage that data itself, or maybe it relies on some deeper class architecture (i.e. other objects taking care of the underlying model) to get this. That part depends on your design. For smaller scenarios having the data source simply have the data in an array or dictionary is enough. Furthermore, a lot of designs actually use a UIViewControllerto adoptUICollectionViewDataSource`. That may be sufficient, but be careful not to blow up your view controller to a monstrosity that does everything. That's just a general tip, you have to decide on your own what is "too much".
Now to your actual intention: To move around cells you don't need to get them. You simply tell the UICollectionView to move whatever is at a given index path to some other index path. The according method is moveItem(at:to:). This works even if cellForItem(at:) would return nil for one of the two index paths. The collection view will ensure the cells are there before they become visible. it does so relying on the data source again, more specifically its collectionView(_:cellForItemAt:) method. Obviously that means you have to have your data source prepared for the move, i.e. it needs to return the correct cell for the given index. So alter your data source's internal storage (I assume an array?) before you move the items in the collection view.
Please see the documentation for more info on that. Also note that this is basically how to move items around programmatically. If you want the user to interactively move them around (in a chat that seems weird to me, though), it gets a little more complicated, but the documentation also helps with that.
Based on your question. If the currently visible cells on screen are from 50 to 59, the cellForItem at IndexPath 30 will not be available. It would be nil. Reason being the 30the cell would have already been reused to display one of the cells from 50 to 59.
There would not be problem to move cell from 30 to 31. Just update your array/data source and reload the collection view.
You can access the cell only if its visible for non visible cell you need to scroll programmatically using indexpath:-
collectionView.scrollToItem(at: yourIndexPath, at: UICollectionViewScrollPosition.top, animated: true)
I am looking at the lower portion of this screenshot. If I had something similar to this in my design, what would be the best way to set this up in Swift?
I have looked into UITableView, but that doesn't seem to be quite what I need. Most of the tutorials & articles I've read regarding the UITableView only focus on 1 or 2 columns max, and don't really expand on how to go much beyond that.
I briefly considered just doing a bunch of statically placed labels, but realized that I will not always know exactly how many items are going to be in the table, so I need a more dynamic way of going about it.
Does anybody else have any advice on how I might go about achieving this sort of layout in Swift?
There are several ways...
UITableViewCell subsclass. It's perfect for your purposue, and you can design it's contents following your needs. (No matter if 2, 3 or 4 columns)
Combination of StackView Vertical with StackView Horizontal inside. Each horizaontal view will contains one of your row.
Generate a HTML page and injec it in a SFSafariViewController or WebView.
Static content. A plenty of UILabel. One for each piece of information
In my opinion the best aproach is the UITableViewCell subsclass.
I'm new to IOS development, I have a few questions.
1) What's the purpose of property rowheight on table view cell, I mean it does nothing even if I change its value, it always takes the value from its parent view i.e a tableview property rowheight? It visually changes in the IB but nothing happens when I run the app.
2) What's the purpose of Content View why is it even there? Let's say If I have to make some image equal to the height of the cell it restricts me. Or is there any way a content view can be changed to be equal to the cell height & width? I have to put constraints on the image in relation with the cell which is not the immediate parent of the image and I don't know if this is the correct way to do it.
3)How does Xcode Autocomplete works? like if I want to write a function tableview(_:tableview didselectrowwithindex:IndexPath) and I type tableview it shows a list, what to do next? I mean I can't type the whole fucntion with params or find the func in the huge list.
The height of the cell set at the IB is primarily used for simulation, the views described at IB are normally resized when actually used. E.g. you can set rows height to be 100 for the table view, 30 for some of the cells and keep the whole controller simulating a nice screen of iPhone 6. The same view will be used for all devices and will be scaled accordingly as well as the cells with the help of your delegate.
The content view is there for the reasons directly related to your additional requests. It holds all the content while there other views that accompany your content and are part of the cell like separators, accessory views, slide action views. Without a content view the responsibility of managing all the additional parts would most likely fall on you as a developer and while you might think that that is fine at the simple layouts, a simple enhancement to it would make a huge impact.
Fuzzy autocompletion at Xcode seems to be something Apple is working on now. If you can't wait and find it too difficult to navigate through the list, there are Xcode plugins available that provide fuzzy autocompletion.
Answering the question in the topic:
example: tableview(_:tableview didselectrowwithindex:IndexPath)
if you write tableview it will show all the symbols that start with tableview. For functions, it will show all the functions sorted by the second parameter name (didSelectRowWithIndex).
[EDIT]
it will autocomplete as far as the answer is unique and then show you a list full of options. I don't know any tricks to skip looking through the massive list. But after a while you'll know what you're looking for and it gets faster.
[\EDIT]
when you press tab, it
by the way: the delegate functions names start with the name of the object they're related to.
So UITableViewDelegate functions start with tableview.
as for your first two questions there are tons of answers for those questions on SO. This one seems closely related to yours.
The question is hopefully pretty straight forward. In one of the tabs of my application where I'm presenting a set of data from Core Data, I want to give the user the option of a Grid view or Table view. Both views should share the same custom header with a button in the header that let's them toggle.
I see it in other apps all the time, but couldn't return any searches. I'm getting stuck on how to flip between the 2 controllers based on different classes.
Any help or guidance is much appreciated. Thanks a lot!
Assuming you are using a UICollectionViewFlowLayout, just adjust the itemSize property of your items to be the width of their containing view.
Bam. Instant "table view"
Sure, it's not quite a tableView, and reasonable people can disagree over when a tableView might be more appropriate than a collectionView, but for what you describe (giving the user a choice between rows or grid), it's probably the magic bullet you seek.
I am new to iOS development, and I have been doing a fair amount of research. Unfortunately, as the title of my post suggests, neither possibility seems exactly suited to my needs.
I need a lot of customization with respect to the look and feel of each individual table view cell, and I need for my table to have header sections which are clickable. I would actually like for the section headers to have the drill down quality and not the cells beneath each section header.
To my knowledge, the problem with PFTableViewController is that it doesn't easily allow for multiple sections (even less so if I need for these section headers to be clickable and of a different look and feel from the regular cells.) Furthermore, customizing the PFTableViewCells doesn't seem terribly simple either.
However, if I use the regular UITableView even with Parse as my backend, won't I run into some difficulties with respect to loading, pagination, etc...?
I have a pretty good idea of how I would implement this app with regular UITableViews so I guess here is my question: is it worth it for me to try and figure out all of this PFTableViewController stuff?
I should also mention the fact that my table view controller will not take up the entire view but only half of the screen.
Thanks in advance for any and all advice
It seems that a normal UITableView will suit your needs. If you want to customize the look and feel of individual cells, you can just subclass a UITableViewCell and modify it.
In terms of your needs with the headers, it's hard to say without knowing more about your app, but you want to follow standard user interface conventions. Users don't expect headers to be clickable. Instead, they attempt to traverse information hierarchies by selecting table view cells, which then bring them to new views with more information. Based on your, needs I think that a standard table view controller with some customization is what you want.