I have 100 rows of data but when we i run the code in iPhone Retina(4-inch) simulator i can see only 14 fit on the screen at a time. If i count the number of visible rows then i get up to 13 but it’s possible to scroll the table in such a way that the top cell is still visible and a new cell is pulled in from below. So that makes at least 14 cells.
If you scroll really fast, then I guess it is possible that the table view needs to make a few more temporary cells, but I’m not sure about that.I want to know after how many cells a cell get reused?
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I am using Xamarin iOS and my table view contains multiple types of cells.
All the cells have dynamic height and different contents with multiple sections.
Here suppose I have total 10 cells out of which few are visible and others are hidden. Based on user action, It depends on whether to show or hide the cell.
In this scenario, If the number of cells is less, It's somehow working fine. But flickering and blank space are showing when the number of cells increases.
You need to reload only appropriate section or even rows instead of reload whole tableview.
Please checkout this solutions.
Reload sections in UITableView
I have a UITableView that reads information from CoreData via the proper mechanisms (using a FetchedResultsController, etc). This information is either textual, or a URL to a local image to load into the tableview.
Data needs to be populated in the table in a bottom-up fashion (similar to a messaging app). I am targeting iOS 8+, but if I use estimatedHeightForRowAtIndexPath, I get terrible jerkiness on 3+ multi line labels and images. The estimate seems way too far off unless it's a one line UILabel. My hunch is that the cell height is being estimated in a top down manner, such that cell heights are growing from top of cell to bottom of cell. This means that scrolling top to bottom is fine, but bottom to top is not, since the cell is being resized "downward" dynamically as I scroll upward.
I am currently using heightForRowAtIndexPath to calculate cell heights. The problem with this is that it takes a very long time for the view to initially load because cell heights are all calculated at once. I am using cell height caching to store cell height so that once the view has loaded, scrolling is buttery smooth.
So my question is this: how do you use heightForRowAtIndexPath without taking the 3-5 second initial load hit?
And follow up bonus question, is there any way to reliably use estimatedHeightForRowAtIndexPath when you have cells that are vastly different in height? We're talking anywhere from 44px to 300px. From what I've read, I can't use the estimatedHeight calculation at all in this situation.
I've exhausted all of the stackoverflow posts concerning estimatedHeight/heightForRowAtIndexPath and I'm now starting to look at the same posts more than once. So I'm stuck.
why woncha stuff a few rows in the table to populate the visible area and after
the viewDidAppear start stuffing older messages on top of the table one or two
at the time with animation none, automatic or whatever.
this way with the postponement of the uitableview population
me thinks you'd get a passable performance.
or you could do it the skype way, postponing population of the table
with older messages until after table bounces off the top edge.
I have a UITableView into which I populate a small number of static UITableViewCells (about 6 cells). I am not using storyboards. Each of these cells is a custom UITableViewCell, has a different layout, so I my thought is that cell reuse is never going to happen in this case.
So I am creating these cells beforehand and storing them into an NSArray. In cellForRowIndexAtPath I just return the corresponding cell that is already stored in my array.
Everything works fine with this approach on iOS6. However on iOS7, the visible area of the table view goes completely blank. When I scroll up, the part of the table view that was underneath the main view previously shows the cells (partial cell if the cell was partially underneath before). But the initial visible area of the table view still remains blank.
Two questions here - Is it fine to store the cells in an NSArray and return them in cellForRowAtIndexPath? As I mentioned earlier, the number of cells is small and each cell is unique, no reuse is going to happen while scrolling.
And what is going wrong in IOS7?
Context:
Building an app that populates a table that takes in data from a asyc json dump.
The cells are of a custom class (I defined). The main label in the cell can be very long.
It is "placed" in storyboard within a prototype cell but customized via code (pretty standard stuff).
Labels are resized in cellForRowAtIndexPath and rows are resized via heightForRowAtIndexPath -- rows are resized by forcing a call to cellForRowAtIndex like Massimo's answer here
So per the question at hand - I've noticed some interesting (bad) things that happen.
First issue: When the table loads, the rows and labels are dynamically resized correctly! Great! However, when I scroll down and then scroll back up, the label heights will be incorrect -- (for example) the first row was correct at loading. Then when I scroll down and then scroll back up to see it again, it will be truncated. Specifically, the row size will be fine but the label height will change and become truncated to 2 lines only. Wondering if this is because I did both storyboard and coding to customize the cell. Anybody see this before?
Second issue: When I scroll down, while the rows are sized correctly (large), the labels are short (truncated.) Wondering if it's some reverse of the above "potential answer".
"potential answer" is that the rows are all calculated and stored "up front" so that scrolling down/then back up doesn't affect it. However, when cells go "out of view" and are dequeued then when they re-viewed (scroll down/then back up) it will rely on the storyboard.(inappropriately?)
All three of your issues are symptomatic of returning the wrong height in heightForRowAtIndexPath. In my data model classes I have a calculateHeight method that I call in heightForRowAtIndexPath. The model also caches the answer so it doesn't have to recalculate it after the first call. The cell class uses the model's calculated height to layout its subviews.
"ANSWERED" by deleting the prototype cell from the storyboard and making them fully in code, the issue went away. The fundamental workings are still not understood (ie. the interactions between storyboard vs. code when cells are put queued and then viewed again)
I've implemented a pull down to refresh that sits above my UITableView.
However, UITableView also has a default setting where if you push up (to reveal rows at the bottom of the table), it also reloads the table data. Since I already have pull down to refresh, I want to disable this. How do I do that?
Thanks!
EDIT: I want to load all the rows of the UITableView at once, not just the visible rows, because I'm not loading too many rows anyway.
It's not that it's "reloading" the cells. If they have been dequeued, then they are being loaded. If you don't want those cells there, then why do you have them in the first place? If you scroll them off the screen they normally get dequeued to improve performance of the tableview. If you don't want this behaviour, then you may not want to dequeue your cells, but tableview performance could be drastically affected.