I am working with open source iOs app and came across this:
queueReusableCellWithReuseIdentifier
How do you use this? I kind of think I may have an idea of it - perhaps it is a variable that is passed through multiple times? Do you use it each time? I'm a beginner, so any help will be appreciated. Thank you so much!
Think about all the cell of a table view exists in an array of cells.
Once the table view wants to load a cell it calls this method with the indexPath (to insert it into the right index) and identifier to recognise the cell (if you have multiple cells)
Now, if the this method return nil. Then the "array of cells" does not contains a cell that can be reused, and the a cell needs to be initialised.
This method if for performance issues mainly, so you will not have to instantiate a instance of a cell every time you want to load a cell.
Related
I am making an interface which have UITableView with four custom UITableViewCell's. And every other UITableViewCell have also UITableView. This mean I have TableView inside a TableView.
Let me call first tableView - ParentTableView and nested tableView - ChildTableView. So I implemented method didSelectRowAtIndexPath on both tableView's. But when the app is running, only the method of the ChildTableView is being called. I need to know inside the ParentTableView, which cell is being tapped.
How can I transfer that information further from ChildTableView to ParentTableView.
This may be a silly question, but I can not find any reliable solution so far, so please help me.
Thank You in advance, kind Sir
First, I think nested table views is a bad idea. But I don't know your use case, so it might be an exception.
The table view controller class used inside a cell have its own #protocol definition and set the outer table view as its delegate. In the inner didSelectRowAtIndexPath: it can inform the outer table view about the selected indexPath, its own indexPath and any other information you might want to transmit.
Try using collection views. You can do a layout that works like a regular table view and then in the cells that need to have a table, you can make those separate cells with another collection view inside or a table view inside of it.
As mentioned before, it's not easy doing table views inside of cells, and it can be very tricky to get things to work correctly.
This is an old tutorial I wrote which may help and be of guidance. But since then there's been collection views and auto layout, so keep in mind it's very old.
All,
I hope most of you know that with ios7 there is not need to do a null check for tableview reuse
if (cell == nil) {
But unfortunately, because of that the cells are always reinitialized, as we put the code in the same method for initializing values. The problem is only with text fields inside the tableview though.
Let me explain the scenario. I have a table view with multiple rows, and some rows contain multiple text boxes. I populate the textboxes with data from server when the page is loaded. Since the cells are always re-initialized as i explained above, whatever I enter in the field goes away and the server data is re populated once i scroll down and come back to the initial stage. This is because the populating the data code is also in the same place. After fetching a reusable cell it populates the data.
Previously till ios6, we used if(cell==nil) and hence we loaded server data inside the cell and when reusing the cell, this piece of code will never be called.
I have other dirty solutions, but would like to know if someone else has a graceful way of dealing this. Please help.
You just don't store any data in the table view cell but in the model that fills the table cell. This is always the way it should be done.
Looking from the MVC standpoint than the UITableViewCell is a view. Since it is reused by iOS you should use a model to the view.
Yes, this is the expected behavior of UITableView. For performance reasons, cells are reused. Thus, it is your responsibility to populate the views in a Table View Cell every time tableView:cellForRowAtIndexPath: is called.
The thing I don't understand from your question - are you making a network call every single time a cell comes into view? If so, cache the results somewhere. Or, if it's a small amount of data, consider just doing it all in one shot at the beginning (still need to be asynchronous though).
One thing I see a lot of developers do is move a lot of code into UITableViewCell subclasses, which sounds like a good idea because it's modular, but makes solutions for problems like this more difficult. Have the Table View Data Source manage the network calls.
If you need some inspiration, look at Apple's LazyTableImages sample.
I have sample collection view. I am dequeue cell from it by dequeueReusableCellWithReuseIdentifier:forIndexPath:
When ViewController is loaded the OS dequeue 5 cells and load information on it.
When I scroll, another 5-7 cells are dequeued and information is loaded on it.
The second set of loaded cells is coming in foreground with information from first set of loaded cells and the information in them is updated with fresh (right) one after less than a half second.
I am using prepareForReuse for cells, where I reset visibility of all cell components and than load fresh information, but the result is not what I expect, it is what I described above.
Any suggestions?
Thanks.
EDIT: Well if I update cell views with data from dequeueReusableCellWithReuseIdentifier:forIndexPath: all works fine, but if I pass the data to cell and ask cell to modify itself - than I have a problem pointed above.
EDIT 2: Soved. As I imagine - it was stupid mistake. As advice for others - make sure that you pass data to cell in any cases.
Do you have ALLOC statements in cellForItemAtIndexPath? or if using a subclass, do you have any ALLOC's in the subclass implementation? Possibly you seeing ui elements that are not being cleared out.
IOS 6, ARC, trying to see if there is a way to prevent a custom table view cell from being "dropped" from the table list even if the cell is off screen. Yes, Yes, I know, should not be doing this but just experimenting now.
In cell for row at index path....
Tried with re-use identifier = nil. Also, just tried creating the cell every time and then having the cell strong referenced with a local array.
The table will ask for cells that have been "off screen" even if the cell seems to not have been discarded.
Again, understood that this is strange way of doing this.
Any discussions on this? Another way of doing this?
You're right that it will always ask for cells that have been "off screen". If you keep strong references to the cells, you will have to release them yourself.
You could store the cells in an array or dictionary (indexed by row), and return the existing cell if it's in the list, otherwise create a new cell when iOS asks for one.
The design of the app I am working on, specifically the tableview part is quite complicated.
There are around 5-6 methods in which I need to get a reference to particular cell from the table view.
What I do not like is that I have to use the
-tableview:cellForRowAtIndexPath
This is a datasource method and does a lot of heavy lifting. Custom cell configuration, dequeueing, getting data for particular cell..etc.. The point is all this code is executed again,even if it does not make any sense at all. The cell object is completely loaded already.
Am I right in my observation and if yes, is there a working tested and lightweight solution?
Perhaps there could be an index of references to all cells. Asking it, I would immediately get the reference without the datasource code.
UITableView has cellForRowAtIndexPath: method.
From UITableView reference:
Returns the table cell at the specified index path.
- (UITableViewCell *)cellForRowAtIndexPath:(NSIndexPath *)indexPath
Parameters
indexPath The index path locating the row in the receiver.
Return Value An object representing a cell of the table or nil if the cell is not visible or indexPath is out of range.