I want to access/update UITableView cell (using reusable cells) which is not in the current view . I know the table view cells are reusable, that can be the reason I am unable to fetch them but is there any way of virtually making and updating. OR I have to drop the reusable cell technique. Suppose tableview have total 20 cells but only say 7 are visible in the current view of iPhone. How will i update other 13 cells which are out of view bounds
Accessing and modifying cells (even if you could) would be a bad pattern. UITableViewCells are designed to be created and modified solely in the tableView:cellForRow:atIndexPath datasource method, where framework automatically asks you what to do with cells that are about to be displayed.
The whole idea behind reusability is that the system takes care of the view for you, and all you need to do is take care of your datasource and instruct the system, using the model, how to render cells, in its allocated datasource method.
This paradigm would be defeated if we started accessing cells manually and modifying them.
You can't access those cells because they are not added to the UITableView but are kept in a queue until user scrolls to them, then they are added to the UITableView. Instead update your model, which will reflect changes on the cells.
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I create my table view cells in xib files that I then register with my table view and return in cellForRowAt using the tableView.dequeueReusableCell method. In the rare instance I create cells by subclassing them and manually programming the interface I usually just initialise them and return them from within cellForRowAt.
I recently discovered that you can register subclasses using tableView.register(cellClass: AnyClass?, forCellReuseIdentifier: String). Should I be registering my subclasses and returning them via dequeueReusableCell? What are the benefits of using it instead of returning an initialised subclass?
You have to always register cell(via code or in storyboard). The Reusability principle is the most important in iOS Table and Collection views.
It means that the table view draws and stores in the memory only few cells that are currently visible + several that mat be visible in the nearest future. If you will not use reusability you will have a big performance problems with big amount of cells.
Also don't forget to clean cells ui in prepareForReuse method in cell subclasses
Yes, you should be taking advantage of the cell reuse system. The reuse system allows the system to very rapidly respond to scroll actions on your table. Instead of having to instantiate a whole new cell from scratch the system can just take cells it already has and update their content.
Bypassing that system by making a whole new cell every time is not an ideal use of resources and with more complex cells can result in noticeable lag on your table view.
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 need to display a table with in my iPhone app:
neither the number of cells nor the contents are known at compile time, but only at run time.
Views for each cell may differ, one cell has textField and another may have some other view control.
Should I consider Static or prototype cells?
Should I consider tableViewController or viewController with tableview in it?
Any thing I need to consider before I start coding? Thanks in advance
For The issue of dynamic Number of cell at Run time, you can call reload data for table view at any time you have the data source ready.
Prototype Cells should be used with no problem.
Simple Table View will be sufficient for the task.
You have to make cell, either in code or in storyboard, for each type of cell you want, 1 table View can have multiple types of prototype cells, Just name them differently and then make the objects of only the specific cell of which the data is best suited.
It is not that difficult but do handle the data source with extreme care.
Should I consider Static or prototype cells?
If you know all possible subview combinations that your cells might need to display the data appropriately, and they are relatively few, make one prototype for each. for example:
One text field,
Two labels,
One image view and a label,
...etc.
Otherwise, just use the plain-vanilla UITableViewCell (no subclassing) and remove/add subviews at runtime when reusing them (that is, inside the method -tableView:cellForRowAtIndexPath:).
Should I consider tableViewController or viewController with tableview
in it?
The only reason I would choose UIViewController + UITableView over UITableViewController is if -for example- I needed the table view to only take up part of the main view's bounds/screen, and display some other subview in the remainder. Otherwise, you get so much "for free" with UITableViewController that there's just no point in implementing all of that from scratch.
You have to choose prototype cell, u can create different types of cell depending upon your requirement.Any think ok for u, u can create tableview controller or view controller.
I'm new to iOS and MonoTouch, and I have a pretty basic need - I have two vastly different views to display in the same table cell depending on whether it is selected or not. When you load the app I'll present a list of products in a custom UITableView, with all the rows deselected and each row basically just showing the product names in a label. As soon as a user taps one of the rows and selects it, I show a very different view with more of a shopping cart layout. Since the two views are so different they have vastly different sizes. What i need is for the cell itself (or row?) to grow and shrink according to the natural height of whichever view is currently being displayed.
I'm using descendants of UITableViewController, UITableViewSource, and UITableViewCell for the solution. What I do is add both versions to the cell's ContentView, then set the Hidden property as needed when the cell/row is selected/deselected to show the right layout. That works well. I'm in demo mode right now, so I'm not overly worried about efficiency or responsiveness, that will have to come later.
I know that GetHeightForRow is responsible for sizing the rows but it only gets called once, when the cell is first shown. It seems to me that I need to alert the TableView to re-poll the source for a new size as the views are changing, but I can't figure out how to do it.
I tried (rather hopefully) to cause GetHeightForRow to be invoked again manually using Cell.SetNeedsLayout and Cell.SetNeedsDisplay, hoping that would cause the table to re-query the source for new dimensions, but no joy.
I tinkered with the direct approach, trying to size the contentview itself but it didn't seem as if it was leading anywhere. I feel as if the table needs to be told to query for a new row size, but I'm open to any suggestions.
Surely I'm not the first to attempt this? What am I missing?
Try forcing GetHeightForRow to be called again by calling ReloadRows instead.
You may or may not have to specify begin/end updates (this might just be for animation, though?)
tableView.BeginUpdates();
tableView.EndUpdates();
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.