Inside my cell for row at indexPath, I have been using the following code to do most of my work because that is what I have been taught. I was wondering, is it necessary to always use if let to do this work? Because I never find that I ever fall into the else statement.
When would I need to use if let or just let inside cellForRowAtIndexPath?
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
if let cell = tableView.dequeueReusableCellWithIdentifier("myCustomCell") as? myCustomCell {
} else {
return myCustomCell()
}
}
UITableView has two dequeue modes:
dequeueReusableCell(withIdentifier:): The table view tries to dequeue a cell. If there are none, it will try to create one using the cell you registered with the reuseIdentifier. If you didn't register a cell, it will return nil giving you the chance to create one yourself.
This is where the else clause in your code would come into effect. Basically never, since presumably you did register a cell class. Most likely in the Storyboard (by setting the identifier in the inspector) but you can also do it in code.
dequeueReusableCell(withIdentifier:for:), note the additional parameter. The table view tries to dequeue a cell: If there are none, it will try to create one using the cell class you registered using the reuseIdentifier. If you didn't register a cell, it will crash.
Solution
If you can guarantee that a) the cell is correctly registered and b) the type of the cell is set correctly, you would generally use the second option. This avoids the exact issue you're having:
let cell = tableView.dequeueReusableCellWithIdentifier("myCustomCell", forIndexPath: indexPath) as! myCustomCell
(However, it is still perfectly fine to use if let even in this case.)
Related
I am new to the iOS programming scene and I recently came across some code examples online of implementations like:
functableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
var cell = tableView.dequeueReusableCell(withIdentifier: customCellIdentifier, for: indexPath) as? CustomCell
if (cell == nil) {
cell = CustomCell(style: UITableViewCell.CellStyle.default, reuseIdentifier: customCellIdentifier) asCustomCell
}
...
}
Where the author tried to handle the event where dequeueReusableCell return nil.
But from my limited personal experience with UITableView and custom cells, I have yet to encounter a time when dequeueReusableCell returned me nil.
From researching, I found the reason could be
"The dequeue… methods try to find a cell with the given reuse
identifier that is currently offscreen. If they find one, they return
that cell, otherwise they return nil."
from MrTJ's answer here
But that has never happened once to me. When I purposely give it a wrong identifier, a runtime error would occur but not once was nil returned. I wonder when exactly that would happen and if handling it is really necessary.
That code isn't correct. The older form of dequeueReusableCell without the indexPath parameter returns nil when there isn't an available cell in the reuse pool (i.e. when the table view first appears). In that case it is your responsibility to allocate a cell.
The newer form of dequeueResuableCell, shown in your question, will always return a cell as it allocates a cell if required.
The expression in your question can return nil if the conditional downcast fails (that is, the cell that was returned wasn't an instance of CustomCell).
I would argue that this represents a serious misconfiguration somewhere and should be found during development. For this reason a forced downcast is normally used; during development you get a crash, fix the problem and move on.
let cell = tableView.dequeueReusableCell(withIdentifier: customCellIdentifier, for: indexPath) as! CustomCell
The code in your question is some sort of Frankenstein mixture of the old and the new.
I have two UITableViewCells and displaying them based on condition in
cellForRowatIndexPath. Both cells related to a creation of a post and than displaying them in UITableView.
In cellForRowAtIndexPath method i don't have any issues to use condition to display cell.
For example:
if postType[indexPath.row] == "Regular" {show this sell }
else {show another}`
This is working perfect. postType array is created during the post creation.
The issue that i have is to show a proper cell outside of cellForRowAtIndexPath method.
I have a button and when user click on it they would be going to the proper cell, just like they would click on the cell it self. However I don't know how to condition an array at proper indexPath or maybe there other way. I'm not that good because just starting out to learn swift.
I can do for a one cell but i want a condition first and than display a proper cell.
This statement works for a one cell.
#IBAction func usernameBtn_click(_ sender: AnyObject) {
let i = sender.layer.value(forKey: "index") as! IndexPath
let cell = tableView.cellForRow(at: i) as! postCell
}
In my case I have two cells. How to have a condition based on post type value in array and have a proper index inserted to check the value and than display a cell.
I have these two cells:
let cell = tableView.cellForRow(at: i) as! postCell
let cell = tableView.cellForRow(at: i) as! moreinfoCell
Any suggestion would be helpful.
You mention that the button does the same as if the user selects the cell so if you have that working just deselect "User Interaction Enable" of your button.
In interface builder:
Programmatically:
button.isUserInteractionEnabled = false
Doing that the touch will be done on the UITableViewCell and the didSelectRowAt indexPath: method will be fired.
I'm working through an exercise which uses tableviews. I noticed within a test during the exercise, they use a method I haven't needed in the past when implementing tableviews from storyboards. The method is:
func register(AnyClass?, forCellReuseIdentifier: String)
After reading the short description of this function in the reference pages. I'm curious to know what does apple mean by term "registers"? I half assume that since we are doing this exercise programmatically at the moment, this function is only needed if you're creating UITableviews programmatically. If this statement is incorrect, please let me know as I'd like to learn more.
Here is the code from the example:
func test_CellForRow_DequesCellFromTableView(){
let mockTableView = MockTableView()
mockTableView.dataSource = sut
mockTableView.delegate = sut
mockTableView.register(ItemCell.self, forCellReuseIdentifier: "ItemCell")
sut?.itemManger?.add(ToDoItem.init(title: "Foo"))
mockTableView.reloadData()
_ = mockTableView.cellForRow(at: IndexPath.init(row: 0, section: 0))
XCTAssertTrue(mockTableView.cellGotDequeed)
}
The DequeueReusable methods are there to check if any reusable cells are left before creating new ones. Hope you have an idea about the working of reusable cells
What happens when the queue is empty? Now we do need to create a cell. We can follow 2 methods to create a cell,
Create cell manually
Create it automatically by registering cell with a valid xib file
METHOD 1
if you do it with manually, you must check cell is empty or not after dequeueReusableCell check. Just like below,
// create a cell for each table view row
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// Reuse an old cell if exist else return nil
let cell:UITableViewCell = self.tableView.dequeueReusableCell(withIdentifier: cellReuseIdentifier) as UITableViewCell!
//check cell is nil if nil you want to allocate it with proper cell
if(cell == nil){
//create cell manually
cell = UITableViewCell(style: UITableViewCellStyle.Subtitle, reuseIdentifier: "CellSubtitle")
}
// do stuff to the cell here
return cell
}
METHOD 2
We could create the cell manually like above which is totally fine. But it would be convenient if the table view would create the cell for us directly.
That way we don't have to load it from a nib or instantiate it.
For registering a cell with a xib or class we use func register(AnyClass?, forCellReuseIdentifier: String) method. Let see an example,
override func viewDidLoad() {
super.viewDidLoad()
self.tableView.register(MyCell.self, forCellReuseIdentifier: "Cell")
}
// ...
override func tableView(tableView: UITableView!, cellForRowAtIndexPath indexPath: NSIndexPath!) -> UITableViewCell! {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath:indexPath) as MyCell
// no "if" - the cell is guaranteed to exist
// ... do stuff to the cell here ...
cell.textLabel.text = // ... whatever
// ...
return cell
}
You are "registering" your custom Cell class - ItemCell - for reuse as a cell for your tableview.
See: https://developer.apple.com/reference/uikit/uitableview/1614888-register
"Register" tells XCode that the cell exists. A cell is registered under a "reuse identifier." This is a unique string that corresponds to your TableViewCell, in this case ItemCell.
A cell can also be registered in the Storyboard by filling out the "Identifier" in the cell's attributes inspector.
I have setup a segue that will show a view controller with a small TableView. I want a different segue to show a bigger TableView but I want the bigger table to have the same exact info as the smaller table. Got the smaller tableView working perfect on its own, but once I give the bigger table a Data source, reset and try it out.....crashes.
// IndexPath or First Cell in TableView
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
var cell = UITableViewCell()
if self.TaskTableViews.hidden == false {
cell = tableView.dequeueReusableCellWithIdentifier( "FirstTask" , forIndexPath: indexPath) as UITableViewCell!
let list = frc.objectAtIndexPath(indexPath) as! List
cell.textLabel?.text = list.taskName
cell.textLabel?.textColor = UIColor.whiteColor()
TaskTableViews.backgroundColor = UIColor.lightGrayColor().colorWithAlphaComponent(0.55)
TaskTableViews.layer.cornerRadius = 8
TaskTableViews.separatorColor?.colorWithAlphaComponent(2.0) }
if self.TaskTable2.hidden == false {
cell = tableView.dequeueReusableCellWithIdentifier( "Second Task" , forIndexPath: indexPath) as UITableViewCell!
let list = frc.objectAtIndexPath(indexPath) as! List
cell.textLabel?.text = list.taskName
cell.textLabel?.textColor = UIColor.whiteColor()
TaskTable2.backgroundColor = UIColor.lightGrayColor().colorWithAlphaComponent(0.55)
TaskTable2.layer.cornerRadius = 8
TaskTable2.separatorColor?.colorWithAlphaComponent(2.0) }
return cell as UITableViewCell
}
The problem is that the code for your two tables is slamming into each other. To fix this, rejigger your logic. Do not make your logic depend on what is hidden. You can handle only one table at a time; just one table is calling here. That table comes in as the tableView parameter. Make your logic depend on that. Depending what table view that tableView parameter is, configure the cell and return it for that table view.
I think that you should consider changing your approach by just resizing the table view dynamically when you go from one scene to the other instead of having two table views if the information is exactly the same.
If you're still pushing for this approach then don't make the condition be that the table view is hidden and instead implement your own logic or boolean to determine this. But again, I'd rather resize a single table view as needed.
You have many problems in your code
1.
var cell = UITableViewCell()
What's the point of this line?
2.
cell = tableView.dequeueReusableCellWithIdentifier( "FirstTask" , forIndexPath: indexPath) as UITableViewCell!
What's the point of casting? This function returns UITableViewCell (not even optional)
3.
cell.textLabel?.text = list.taskName
Should not compile, cause UITableViewCell doesn't have textLabel
4.
TaskTableViews.backgroundColor = UIColor.lightGrayColor().colorWithAlphaComponent(0.55)
What's the point of doing this every cell request? Move this to viewDidLoad or other appropriate place
Your if { } parts are identical except of reuse identifier
Use tableView argument when needed
Use if { } else
8.
return cell as UITableViewCell
Why cast? Just return
I'm sure I haven't found all of them))
I'm trying to create an autocompleter using iOS 8, Swift and Xcode 6.3
I have a problem that I'm trying to solve, but I gave up... I hope someone can help here. The problem is that (custom) UITableViewCell's are not displaying when the initial dataSource is empty. When adding data to datasource and reloading the tableView, the cells SHOULD display, but they don't... At least, the first time they don't... A second time, they DO... When I initialize the table with non-empty data, the problem doesn't occur. I guess something goes wrong with dequeueReusableCellWithIdentifier. In beginning, no reusable cells are found, or something. But I don't know why...
Relevant code, in ViewController.swift:
// filteredWords is a [String] with zero or more items
#IBAction func editingChanged(sender: UITextField) {
autocompleteTableView.hidden = sender.text.isEmpty
filteredWords = dataManager.getFilteredWords(sender.text)
refreshUI()
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell") as! AutocompleteTableViewCell
cell.title.text = filteredWords[indexPath.row]
return cell
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return filteredWords.count
}
func refreshUI() {
self.autocompleteTableView.reloadData()
}
I created a sample project on github:
https://github.com/dirkpostma/swift-autocomplete
And a movie on YoutTube to show what goes wrong:
https://www.youtube.com/watch?v=ByMsy4AaHYI
Can anyone look at it and spot the bug...?
Thanks in advance!
You've accidentally hidden your cell.
Open Main.storyboard
Select Cell
Uncheck Hidden
Side note: As for why it's displaying the second time around with the cell hidden? It appears to be a bug. It should still be hidden (print cell.hidden, notice it's always true despite showing the text on the screen).
I think you need to change your code. Check out below code. It is because if you remember in Objective C you needed to check if the Cell was nil and then initialise it. The reuse identifier is usually reusing an already created cell, but on the first launch this does not work because there is no Cell to use. Your current code assumes always that the cell is created (re-used) because you are using ! in the declaration, so if you use the optional (?) it can be null and you then can create the cell
var cell = tableView.dequeueReusableCellWithIdentifier("Cell") as? AutocompleteTableViewCell
if cell == nil
{
//You should replace this with your initialisation of custom cell
cell = UITableViewCell(style: UITableViewCellStyle.Value1, reuseIdentifier: "CELL")
}
cell.title.text = filteredWords[indexPath.row]
return cell