I populate the tableview using the data from the webservice.
Now lets say. Initially I got the 20 objects in array. So I populated 20 cells in table.
Now I scroll up the tableview and reach the last cell. Then I call webservice to call more records. This time I again got 20 records. So I populate them to table view.
Now I have array count equal to 40. If this goes on. The array size will go on increasing, which might create performance issue or memory issue.
So please tell me what is the best approach to handle this situation when I am working on native code.
Thanks.
Your approach is good and right, now it creates some cell reload problem when you have image in cell which are downloaded from server. So the best approach is add you data in array as you have describe. Just check if your cell is nil then set all data to that cell, and if cell is nil then just return cell, don't do any thing for that cell. It will just refresh your all downloaded set of array's data. In you case it will reload first 10 cell, and for next 11-20 data it will skip 0-9 cell and load from 10-19 cell.
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I'd like to get every data that is within all cells in one tableview which is quite a long list.
I'm looking for an approach on how to retrieve everything including those hidden in view, which I know the views are reused. I think some of you might have experienced this problem before, what are your approach on this?
I've tried
let cells = self.tableView.visibleCells
then looping into every cell and saving each data to an array but it is not effective in getting those that aren't part of the view or hidden. Is there a way to get over this?
In cellForRowAtIndexPath, YOU are telling the table what is in each cell. So why would you turn around and ask the table what's in each cell? If the user puts "Hello" in your first cell, then scrolls the table enough to push that first cell out of view, then when the user scrolls back to the top, YOU are the one telling it to put "Hello" back in that first cell. YOU own the data source, not the table.
You need a data source. That can be "empty" at first, maybe an array of empty strings if that's what you want (each index in the array could map to a table row for example). But then, as the user interacts with the text fields in the cells, you need to update that data source with the text they entered.
You should use that data source as your source for the cellForRowAtIndex method. That way you can handle populating the cells when they are requested by the table, and you also know all the data when the user is done.
Why not just update the model each time the user taps a key when editing a textfield? You could create a protocol for that cell subclass and make your view controller the delegate for each cell. As long as cells are guaranteed to stay on the screen while you're typing (you'll get some weird behaviors if not) the cell can send a message to the view controller or whatever you hook it up to telling it what new value to store. Then everything is already stored for you when you need the full list, and you don't have to interact with the tableview.
Hi I am tying to iterate through all the cells of my tableview but My tableview variable only let's me access the visible cells. so is there a way to declare the tableview without using the dequeuereusableCellWithIdentifier? or is there a way to iterate through all the cells?
Thanks,
To efficiently display a table, cells are used and reused depending on which ones are visible onscreen. In fact, this is what dequeuereusableCellWithIdentifier is suggesting - you specify different types of cells so they can be recycled later, as new ones are displayed and the components of offscreen ones are available for reuse.
You should define what needs to be changed or retrieve cells using table view cellForRowAtIndexPath.
You Are Already Accessing All The Cells In The TableView.
Note: I lied, two or more cells may be kept for quick reuse as well by tableView, but are not shown immediately.
At a time, a tableView only shows limited amount to cells to maintain performance and memory usage. So, for this purpose dequeuereusableCellWithIdentifier() method is utilised to let iOS handle the reuse of cells when necessary.
This way, no matter how large the dataSource, from 100,1000 to 1M, for the tableView, it will show the data in its cell smoothly and without any hiccups. That is why, you have limited cells visible and only those are the total cell used and reused by the tableView again and again.
By this definition, the total cell in use are the total visibleCells. So, when you are accessing the visibleCells, you are already accessing all the cells tableView has in use.
If you want to access all the data used by the cell, then please access the dataSource of tableView, not the visibleCells only.
Kind Regards,
Suman Adhikari
I want to loop through a TableView and extract the text from all the selected rows. I suppose I "could" create and maintain a special array that is updated every time a row is selected/deselected using the didSelect/didDeselectRowAtIndexPath methods. But creating a separate array seems like an extra step. Is there no way to let the TableView itself serve as the array and then simply loop through it and get the selected rows? What would the code look like? I'm new to Swift, so this might be a silly question.
Part of the problem is that cells are supposed to be reused, and when used this way it is not possible to loop through them all. You could get around this by using a unique reuse identifier for each cell, such as the indexPath itself or some underlying unique id in your model. Then, you could indeed loop through all cells and retrieve whatever state you desired from each.
You would, however, find your application crushed under the weight of too many cells being instantiated and kept in memory. If you don't have many cells you won't be killed, but try it with a big data set and your app will enjoy a very quick death.
It is far more efficient to store one array with a bunch of id's than a large number of memory-intensive UITableViewCells.
As mentioned in comments, you should work with underlying datasource, not the table itself.
For example if your table shows rows from Array, it is way more faster to retrieve strings directly from that array than creating UITableViewCells and get strings from them.
Get indices of selected rows using UITableView's property indexPathsForSelectedRows.
Query datasource for each row.
As has been said the tableview only handles displaying, your datasource is what powers the data shown if you think about it.
Plus as said before the tableview dequeues cells as they scroll on and off the screen.
The best way to achieve what you want is to add a property to your datasource for each element that will allow you to filter out the select properties easily.
How are you storing the state for each selected cell currently? As this is the same functionally you would use to be able to generate your selected text array.
I am getting really frustrated trying to solve this problem i tried implementing it in many many ways but no solution. I have a UIStepper in a custom cell and i want to change a value on the cell. Everything works fine expect when i scroll around the tableView the values from the UIStepper changes from one cell to another. Please help here are my screen shoots.
Link to tableview implementation and link to cell implementation
You are trying to store the stepper value inside each individual cell. That's not going to work because cells are reused; the cell that you now see in row 2 may reappear in row 20 when the user scrolls.
That is why you must store the value for the stepper in the model (your data) on a row-by-row basis, so that you can set it freshly and correctly for that row every single time cellForRowAtIndexPath: is called.
This, in turn, means that as the user steps the stepper, its valueChanged is going to need to talk to the table view data source so that the model can be updated ("the stepper value for row 5 has just been changed to 3") and maintained in the model.
I have a UITableView that collects data from a database. What I would like to know is if there is some way I can iterate in the UITableView collection and check the values of the cell? The reason I ask is because I would like to update each cell based on the current value that it has (change font, size, color, etc.). I've seen in another SO post regarding this topic, but since the cells are already created and their values are changed it is a bit harder for me. I was thinking of iterating through the UITableView before I call reloadData, but any other suggestions are welcome.
You should not iterate over the cells of UITableView, because some of them (in fact, most of them) may not be present until you request them. UITableView aggressively recycles its cells, so if a cell is not visible, it is very likely that you would be creating it from scratch only to put it back into recycle queue moments later.
Changing your model and calling reloadData the way your post suggests would be the right solution. iOS will ensure that it runs the update in a smallest number of CPU cycles possible, so you do not need to worry about the cells that are already created. This is also the easiest approach in terms of your coding effort.
A table view is for displaying data. The properties of your table cells should only be written to, not read from. The appropriate way of handling this situation would be to update your underlying model objects -- the objects that you use to populate the table view -- as the data changes, and then reload the affected rows.
The issue you'll encounter is that UITableView reuses table cells. Once a table cell scrolls off the screen, it's quite likely that the table view will reuse the same cell to display a different row.
This means it's fundamentally not possible to iterate over the table cells. When you need to refresh a row because its data has changed, you should call reloadRowsAtIndexPaths:withRowAnimation: (or reloadData if all rows have changed) and if the row is visible on screen, UITableView will call your data source methods and give you an opportunity to configure the cell for display.