I am an iOS developer and I am currently developing an app using UITableView. The last row of the UITableView contains a button.
But there was a problem here. I put the move (moveRowAt) function in the row, and I can move to the last row! The last row should not be moved. It should always be located in the last row. The last row must have 'moveRowAt' disabled.
I looked up a lot of information, including Stack Overflow, but I did not get any clues.
maybe I could do a bit more than a plain comment by making a sample implementation of making the last row immovable in every section you may have:
func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
return self.tableView(tableView, numberOfRowsInSection: indexPath.section) - 1 != indexPath.row
}
NOTE: if you have your datasource and the number of data accessible anywhere else, it would be more desirable to get the number of rows (in section) from there not by calling the delegate method (as I did here) – however, logically there is nothing wrong with any of the concepts; by the way: here is the class-ref docs of tableView(_:canMoveRowAt:), of you want to know more about it.
At this point, you need to tell the table view that the last row should not be moved. You could achieve this by implementing tableView(_:canMoveRowAt:) data source method:
func tableView(_ tableView: UITableView, canMoveRowAt indexPath: IndexPath) -> Bool {
// '??' means the last row...
return indexPath.row == ?? ? false : true
}
assuming that you are already know the number of rows, you should check the last one.
Furthermore: for your case it might be a good idea to the button as tableFooterView instead of row, therefore there is no need to implement the above method.
Related
I'm unit testing on a tableView whether it renders a cell.
And I found that tableView.cellForRow(at:) returns nil, while tableView.dataSource?tableView(tableView:cellForRowAt:) returns the right cell.
Here's my unit test code.
it("renders one option text") {
let indexPath = IndexPath(row: 0, section: 0)
let cell = sut.tableView.dataSource?.tableView(sut.tableView, cellForRowAt: indexPath)
let cell2 = sut.tableView.cellForRow(at: indexPath)
expect(cell?.textLabel?.text).toEventually(equal("A1")) // test suceeded
expect(cell2?.textLabel?.text).toEventually(equal("A1")) // test failed
}
So I'm curious about the difference of the two methods.
Apple's document says that tableView.cellForRow(at:) returns nil if the cell is not visible, so I'v understood that tableView.cellForRow(at:) returns nil when it's under unit testing,
but I'm not sure the time order of the two methods being called and when tableView.cellForRow(at:) get the right value(cell).
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
This method is used to generate or dequeue the cells as required by tableView. This is not the UITableView member method. Instead, it is a protocol method and another object, which will be a data source, will implement and return the value. So it will always return a cell whether we are unit testing or while debugging the app.
tableView.cellForRow(at:)
This method is not the generator method. It is a member method of UITableView as a utility method for eg. for getting selected row we use tableView.selectedRow. So it is supposed to return cell for any indexPath.
As we know UITableView doesn't create cells equal to rows drawn. Suppose you wanted to draw 100 rows then UITableView only create few extra cells apart from cells which are visible. So if you pass any indexPath which is not among the visible rows then practically that cell doesn't exist. Because tableview is waiting for you to scroll and reuse the unused cells. So whether you are doing unit testing or working on app it will always show nil for cells which are not visible.
tableView.dataSource?tableView(tableView:cellForRowAt:) will always dequeue a new cell. It isn't the one on display unless tableView is the one that called it.
I have a sectioned UITableView. Rather than have each row of the section individually selectable, how to I make it so the entire section (rows plus header view) respond the same if there is a tap anywhere in the section. Suggestions?
This kind of behavior can be supported in different ways. The simplest way to make an entire section have the same behavior is as follows:
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
switch indexPath.section {
case 0:
doBehavior0()
break
case 1:
doBehavior1()
break
// etc...
}
}
Keep in mind that this will not work for headers. You'll have to create a gesture recognizer and call doBehaviorX() from that. More details here. This should be simple enough to implement if you have a fixed number of sections (which I will assume since your question didn't specify).
I'm working through a UITableView tutorial and I've become curious about array iteration as I implement the UITableViewDataSource methods. When we call indexPath.row, is this calling a for loop for us behind the scenes? I'm asking because months back when I was learning to use data from a webservice (I've forgotten the exact steps of how I did it precisely) but I believe I needed to iterate over the array in order to present the information in the console.
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
// Create an instance of UITableViewCell, with default appearance
let cell = UITableViewCell.init(style: .value1, reuseIdentifier: "UITableViewCell")
// Set the text on the cell with the description of the item instance that is at the nth index of the allItems array, where n = row this cell will appear in on the tableview
let item = itemStore.allItems[indexPath.row]
cell.textLabel?.text = item.name
cell.detailTextLabel?.text = "$\(item.valueInDollars)"
return cell
}
Am I correct in thinking that the indexPath.row method is iterating over the array for us behind the scenes?
let item = itemStore.allItems[indexPath.row]
No, calling indexPath.row does not iterate through all rows for you. It's just a variable sent to cellForRowAt that you can access and use to create your cell. It contains information about which row in which section the function cellForRowAt was called for.
However, cellForRowAt is actually called every time a cell is going to be visible on your tableVIew. Imagine you have a dataSource with 100 items and it is possible to only see 10 cells at a time. When the tableView gets initially loaded, cellForRowAt will get called 10 times. Then, if you scroll your tableView to show 3 more cells, cellForRowAt will get called 3 more times.
First of all the tutorial seems to be pretty bad. Table view cells are supposed to be reused
let cell = tableView.dequeueReusableCell(withIdentifier: "UITableViewCell", for: indexPath)
The workflow to display table view cells is:
The framework calls numberOfRowsInSection (and also numberOfSections)
For each section/row pair in the range of the visible cells it calls cellForRowAt and passes the index path in the second parameter.
No. The indexPath is just a struct with a section and a row. You use those to directly look up the information from your array. No iteration is happening.
cellForRowAt is only called for the cells that are on screen, so the order they are called depends on which direction you are scrolling.
In fact, the UITableView doesn't even know if you are using an array, or generating the information on the fly. What you do with the indexPath row and section is up to you.
Check the documentation of UITableView and cellForRowAtIndexpath functions.
An index path locating a row in tableView.
IndexPath will be a structure, which helps you to get the specific location from a nested array. In your case of the table view, rows inside the section.
cellForRow will return a cell for particular index path(in the specified section and row)
So indexPath.section will give the section number for which the cell is going to be modified and returned to the data source. And Inside the section, and indexPath.row will be the corresponding row inside that section.
index path documentation
tableView-CellForRowAt: IndexPath
UITableView DataSource Documentation
[update]
If you want to add multiple sections, add another dataSource numberOfSections, and return the number of sections count from it.
I can link to a create a table view tutorial from Apple, but it's a long document, you can skip the starting and read the To display a section in your table view.
If you want, you can use a 2D array for keeping sections and rows. And in numberOfSections method return array.count, and in numberOfRows:inSection, return array[section].count
More examples,
example
example
thanks,
J
This question already has answers here:
How to detect the end of loading of UITableView
(22 answers)
Closed 6 years ago.
I need to call a function after the UITableView has been loaded completely. I know that in most cases not every row is displayed when you load the view for the first time, but in my case, it does as I only have 8 rows in total.
The annoying part is that the called function needs to access some of the tableView data, therefore, I cannot call it before the table has been loaded completely otherwise I'll get a bunch of errors.
Calling my function in the viewDidAppear hurts the user Experience as this function changes the UI. Putting it in the viewWillAppear screws up the execution (and I have no idea why) and putting it in the viewDidLayoutSubviews works really well but as it's getting called every time the layout changes I'm afraid of some bugs that could occur while it reloads the tableView.
I've found very little help about this topic. Tried few things I found here but it didn't work unfortunately as it seems a little bit outdated. The possible duplicate post's solution doesn't work and I tried it before posting here.
Any help is appreciated! Thanks.
Edit: I'm populating my tableView with some data and I have no problems with that. I got 2 sections and in each 4 rows. By default the user only sees 5 rows (4 in the first section, and only one in the second the rest is hidden). When the user clicks on the first row of the first section it displays the first row of the second section. When he clicks on the second row of the first section it displays two rows of the second section, and so on. If the user then clicks on the first row of the first section again, only one cell in the second section is displayed. He can then save his choice.
At the same time, the system changes the color of the selected row in the first section so the users know what to do.
Part of my issue here is that I want to update the Model in my database. If the users want to modify the record then I need to associate the value stored in my database with the ViewController. So for example, if he picked up the option 2 back then, I need to make sure the second row in the first section has a different color, and that two rows in the second sections are displayed when he tries to access the view.
Here's some code :
func setNonSelectedCellColor(indexPath: NSIndexPath) {
let currentCell = tableView.cellForRowAtIndexPath(indexPath)
currentCell?.textLabel?.textColor = UIColor.tintColor()
for var nbr = 0; nbr <= 3; nbr++ {
let aCell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: nbr, inSection: 0))
let aCellIndexPath = tableView.indexPathForCell(aCell!)
if aCellIndexPath?.row != indexPath.row {
aCell?.textLabel?.textColor = UIColor.blackColor()
}
}
}
func hideAndDisplayPriseCell(numberToDisplay: Int, hideStartIndex: Int) {
for var x = 1; x < numberToDisplay; x++ {
let priseCell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: x, inSection: 1))
priseCell?.hidden = false
}
if hideStartIndex != 0 {
for var y = hideStartIndex; y <= 3; y++ {
let yCell = tableView.cellForRowAtIndexPath(NSIndexPath(forRow: y, inSection: 1))
yCell?.hidden = true
}
}
}
These two functions are getting called every time the user touches a row :
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
let path = (indexPath.section, indexPath.row)
switch path {
case(0,0):
setNonSelectedCellColor(indexPath)
hideAndDisplayPriseCell(1, hideStartIndex: 1)
data["frequencyType"] = Medecine.Frequency.OneTime.rawValue
case(0,1):
setNonSelectedCellColor(indexPath)
hideAndDisplayPriseCell(2, hideStartIndex: 2)
data["frequencyType"] = Medecine.Frequency.TwoTime.rawValue
case(0,2):
setNonSelectedCellColor(indexPath)
hideAndDisplayPriseCell(3, hideStartIndex: 3)
data["frequencyType"] = Medecine.Frequency.ThreeTime.rawValue
case(0,3):
setNonSelectedCellColor(indexPath)
hideAndDisplayPriseCell(4, hideStartIndex: 0)
data["frequencyType"] = Medecine.Frequency.FourTime.rawValue
default:break
}
}
I store the values in a dictionary so I can tackle validation when he saves.
I'd like the first two functions to be called right after my tableView has finished loading. For example, I can't ask the data source to show/hide 1 or more rows when I initialize the first row because those are not created yet.
As I said this works almost as intended if those functions are called in the viewDidAppear because it doesn't select the row immediately nor does it show the appropriate number of rows in the second sections as soon as possible. I have to wait for 1-2s before it does.
If you have the data already that is used to populate the tableView then can't you use that data itself in the function? I am presuming that the data is in the form of an array of objects which you are displaying in the table view. So you already have access to that data and could use it in the function.
But if that's not the case then and if your table view has only 8 rows then you can try implementing this function and inside that check the indexPath.row == 7 (8th row which is the last one).
tableView(tableView: UITableView, didEndDisplayingCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath)
Since all your rows are visible in one screen itself without scrolling you could use this function to determine that all the cells have been loaded and then call your function.
I noticed in that to disable the highlight feature of a table cell you would yse the following method:
override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
...
tableView.deselectRowAtIndexPath(indexPath, animated: false)
}
What I don't understand is what's going on in the first argument indexPath. In the instructional book I've been reading just about every other method has been using indexPath.row for selecting individual cells:
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cellIdentifier = "Cell"
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as CustomTableViewCell
cell.nameLabel.text = restaurantNames[indexPath.row]
cell.typeLabel.text = restaurantTypes[indexPath.row]
cell.locationLabel.text = restaurantLocations[indexPath.row]
}
Just out of curiosity I tried passing indexPath.row as an argument but got the error, 'NSNumber' is not a subtype of 'NSIndexPath'. In this particular case what is the main difference between using indexPath and indexPath.row.
From the NSIndexPath class reference:
The NSIndexPath class represents the path to a specific node in a tree
of nested array collections. This path is known as an index path.
Table views (and collection views) use NSIndexPath to index their items
because they are nested structures (sections and rows). The first index is the section of the tableview and the second index
the row within a section.
indexPath.section and indexPath.row are just a "convenience" properties, you always have
indexPath.section == indexPath.indexAtPosition(0)
indexPath.row == indexPath.indexAtPosition(1)
They are documented in NSIndexPath UIKit Additions.
So NSIndexPath is an Objective-C class and is used by all table view
functions. The section and row property are NSInteger numbers.
(Therefore you cannot pass indexPath.row if an NSIndexPath is expected.)
For a table view without sections (UITableViewStyle.Plain) the
section is always zero, and indexPath.row is the row number of
an item (in the one and only section). In that case you can use
indexPath.row to index an array acting as table view data source:
cell.nameLabel.text = restaurantNames[indexPath.row]
For a table view with sections (UITableViewStyle.Grouped) you have
to use both indexPath.section and indexPath.row (as in this
example: What would be a good data structure for UITableView in grouped mode).
A better way to disable the selection of particular table view rows is
to override the willSelectRowAtIndexPath delegate method:
override func tableView(tableView: UITableView, willSelectRowAtIndexPath indexPath: NSIndexPath) -> NSIndexPath? {
// return `indexPath` if selecting the row is permitted
// return `nil` otherwise
}
In addition, to disable the appearance of the cell highlight on touch-down, you can also set
cell.selectionStyle = .None
when creating the cell. All this is (for example) discussed in
UITableview: How to Disable Selection for Some Rows but Not Others.
Your question and confusion stems from the fact that Apple decided to use somewhat imprecise method name/signature
tableView.deselectRowAtIndexPath(indexPath, animated: false)
The "Row" word in the method signature implies that row is going to be deselected, therefore one would expect a row as a method parameter. But a table view can have more than one section. But, in case it doesn't have more sections, the whole table view is considered one section.
So to deselect a row (a cell really) in table view, we need to tell both which section and which row (even in case of having only one section). And this is bundled together in the indexPath object you pass as a parameter.
So the before-mentioned method might instead have a signature
tableView.deselectCellAtIndexPath(indexPath, animated: false)
which would be more consistent, or another option, albeit a bit less semantically solid (in terms of parameters matching the signature)
tableView.deselectRowInSectionAtIndexPath(indexPath, animated: false)
Now the other case - when you implement the delegate method
tableview:cellForRowAtIndexPath
here again (Apple, Apple...) the signature is not completely precise. They could have chose a more consistent method signature, for example
tableview:cellForIndexPath:
but Apple decided to stress the fact that we are dealing with rows. This is an 8 year old API that was never the most shining work of Apple in UIKit, so it's understandable. I don't have statistical data, but I believe having a single section (the whole tableview is one section) is the dominant approach in apps that use a table view, so you don't deal with the sections explicitly, and work only with the row value inside the delegate method. The row often serves as index to retrieve some model object or other data to be put into cell.
Nevertheless the section value is still there. You can check this anytime, the passed indexPath will show the section value for you when you inspect it.
NSIndexPath is an object comprised of two NSIntegers. It's original use was for paths to nodes in a tree, where the two integers represented indexes and length. But a different (and perhaps more frequent) use for this object is to refer to elements of a UITable. In that situation, there are two NSIntegers in each NSIndexPath: indexPath.row and indexPath.section. These conveniently identify the section of a UITableView and it's row. (Absent from the original definition of NSIndexPath, row and section are category extensions to it).
Check out tables with multiple sections and you'll see why an NSIndexPath (with two dimensions) is a more general way to reference a UITableView element than just a one-dimensional row number.
i see the perfect answer is from apple doc
https://developer.apple.com/documentation/uikit/uitableview/1614881-indexpath
if you print indexpath you may get [0,0] which is first item in the first section
I was confused between indexPath and indexPath.row until i understand that the concept is the same for the TableView and the CollectionView.
indexPath : [0, 2]
indexPath.section : 0
indexPath.row : 2
//
indexPath : the whole object (array)
indexPath.section : refers to the section (first item in the array)
indexPath.row : refers to the selected item in the section (second item in the array)
Sometimes, you may need to pass the whole object (indexPath).