So I have a table view with about 150ish rows in the cellForRowAt method I have the following code
cell.monthLabel.text = String(indexPath.row)
if indexPath.row == 0{
cell.backgroundColor = .blue
}
The question is why at index path 9, 18, 27 and so on have the background color of blue.
Cell are reused, you have to set all UI elements to a defined state.
So if you set the backgroundColor to blue in row 0
if indexPath.row == 0 {
cell.backgroundColor = .blue
}
you have to (re)set it to a default color in all other cases
else {
cell.backgroundColor = .white
}
As you do not show all the code of the tableView(_:cellForRowAt:) method just assume you are dequeuing cells (with the method dequeueReusableCell(withIdentifier:) and have registered you class for reusing (if you use a custom class).
With this approach the view of the cells gets reused. Meaning that if you do not re-set a property (e.g. background color) it will just use the one form the old cell.
To fix this you can easily include a else in your code and in there set the background color to white.
If you subclass the UITableViewCell class you can the prepareForReuse() function to clean up and e.g. reset the background color.
UITableView doesn't set the data on each item once, it keeps setting the data again and again on all visible items according to the activity going on. i can't give you the clear reason for this behavior but I can give you the solution. Whenever you are setting some data on items with some conditions, always use "Else" statement as well. So for this particular issue you just have to do is to add "Else" block with your "If" condition and set the white background of item in "Else" block.
Related
I have created a single prototype cell which has two labels (mainLabel and subLabel) and an uiimageview. In the uitableview I'd like to have several cells which reuse the prototype and when needed the subLabel is hidden and the uiimageview is changed with different one or with a uiswitch. The two labels have different text for each cell. Do you have any suggestions/hints in order to do it? possibly in a mvvm architecture?
I'll describe what I am doing:
I have a struct (the Model) with two properties: label and sublabel. This is then instantiate by a viewModel which provides text for each cell, done by a method called getModel(_ indexPath: IndexPath) -> cellModel { ... }. Finally in UIViewController, in tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) { ... } I am calling getModel(), using dequeueReusableCell and setting up each cell.
In getModel() there is a huuuuge switch which I use to know which cell is which
Then in uitableviewcell I have some method that hides sublabel and changes uiimageview.
It kind of works, however I have some issues with while scrolling. For example, sometimes a uiimageview is drawn in another cell, or a subLabel is hidden, even if it is not supposed to. I guess this is due because it is reusing the cell, and I am not resetting it.
Anyway, any suggestions or ideas?
I know this is overkilling...
No need for any pattern. Yes, you can use that single cell design for all cells. Just hide/empty label(s) and image view as you like per cell.
First of all you have to set default value to both the labels and imageview
i.e. (consider a title label, a sub label and a imageview)
lblTitle.isHidden = false
lblSubLabel.isHidden = false
imgViewIcon.image = nil
Then just show labels in specific condition that you want to match and set image in imageview
i.e. (consider your condition to hide sub label)
if needToHide == true {
lblSubLabel.isHidden = true
}
I am trying to implement a table view design where a user can click a button outside of a table view cell and the display mode of all the buttons should change. However this is not the 'selected' mode for a given cell (that will be yet a third state that becomes accessible via switching to this second state). What's the proper way to accomplish this?
I am using dequeueReusableCellWith so I don't want to simply cycle through every cell because some that are out of sight probably shouldn't be modified. I simply want any cell that is visible, or becomes visible, while the table view cell is in this second display mode to follow a second design rather than the first design.
The second design, for now, is being modified via a method I added to a subclass of UITableViewCell like so:
- (void) p_refreshDisplay {
if (self.editing) {
self.buttonToClearWidth.constant = 20;
self.buttonToClearLeadingWidth.constant = 20;
} else {
self.buttonToClearWidth.constant = 0;
self.buttonToClearLeadingWidth.constant = 0;
}
}
However, I'm not sure how to trigger this p_refreshDisplay for every visible (and to become visible) cell. It seems unwise to call this many times and refresh the table view. What would be the proper way to accomplish what I want to do?
You do what should be done for any table view change:
Update your data model or some flag as needed.
Either call reloadData on the table view or call reloadRowsAtIndexPaths:withRowAnimation: passing in indexPathsForVisibleRows as the list of rows to reload.
Implement cellForRowAtIndexPath to provide appropriate cells for the given data/flags.
It sounds like you should have a custom cell class that has one or more properties that can be set on the cell in cellForRowAtIndexPath so the cell can render itself properly based on the specified state.
You can achieve this by doing three things:
Establish some property that indicates the "mode" of the table, either a boolean or perhaps an enum if there are more than three states
Ensure that cellForRowAtIndexPath configures the cell appropriately based on the value of this property. This will ensure that newly displayed cells are configured correctly.
When the "mode" changes you can use the tableview's visibleCells property to update any currently visible cells:
for cell in tableview.visibleCells {
if let myCell = cell as? MyCustomCellClass {
myCell.setButtonStyle()
}
}
I have a UITableView with a custom UITalbeCellView. Every cell has a title a body and a date. When I fetch the data some of the titles must be red so there is a Bool that is set to true for those cells which title has to be red.
The first time the data is fetched it looks fine, but as you scroll up and down a few times all of the titles end up being red.
Im using an array of structures to store the data and on the cellForRowAtIndexPath there is an if and if the boolean in that position of the array is true I change the color to red:
let cell = tableView.dequeueReusableCellWithIdentifier("CommentsRowTVC", forIndexPath: indexPath) as! CommentsRowTVC
let single_comment = self.AOS[indexPath.row]
cell.titulo_comentario?.text = single_comment.titulo_comment
if single_comment.flag == true {
cell.titulo_comentario.textColor = UIColor.redColor()
}
Im gessing it reuses Views or something like that. Does this have any easy fix? Or do I have to implement my own TableView to prevent this from happening?
Im also thinking the method dequeueReusableCellWithIdentifier might be the one causing my problem... but Im new on swift and cant think of any replacement for that.
It is happening similar thing on buttons there are on the cells, when you click a button from a cell it changes its color and disables it, but just the one on that cell. However when clicking on a cell, buttons from other cells are also suffering those changes.
Since cells get reused you end up with cells that were previously red because they hadsingle_comment.flag == true and are now used for another row where there actually is single_comment.flag == false. You have to reset the color in the else branch again:
if single_comment.flag == true {
cell.titulo_comentario.textColor = UIColor.redColor()
} else {
cell.titulo_comentario.textColor = UIColor.whiteColor()
}
UITableViews reuse their cells, meaning that you will get cells inside your cellForRowAtIndexPath which have previously been used before, maybe have have set the textColor to red. Your job is it now to revert the color of the text to its original state.
In general whatever change you make inside the if-branch of cell-customization has to be undone in the else-branch. If you remove a label in the if, add it in the else.
Screenshot of weird behavior
The screenshot tells is quite well. I have a tableview with dynamic custom cells. I added a println for one of the contents of the cell to check, if the labels are set. I can see in the debug log, that each cell has its content. Still, on the device there are empty cells at random, which means, the row, where no content appears, is changing a lot. Even just scrolling up and down makes the second row disappear, but the third row is filled. Scrolling again turns this around again. If I close the app and start it again, every row is filled correctly.
Here is the code for the cell generation:
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
// Return a count picker cell
if countPickerTableRow == indexPath.row {
...
}
// Return a normal wish list entry cell
else {
let article = wishListEntries[indexPath.row]!
let cell = tableView.dequeueReusableCellWithIdentifier("ArticleCell", forIndexPath: indexPath) as! WOSArticleCell
// Correct the order in case a count picker cell was inserted
var row = indexPath.row
if countPickerTableRow != -1 && indexPath.row > countPickerTableRow {
row--
}
cell.setThePreviewImage(UIImage(data: article.thumbnail))
cell.setArticleName(article.name)
cell.setArticleDescription(article.text)
cell.setArticleNumber(article.number)
cell.setArticleCount(article.count as Int)
cell.setOrderInTable(row)
cell.setTableViewController(self)
cell.setNeedsDisplay()
cell.setInputAccessoryView(numberToolbar) // do it for every relevant textfield if there are more than one
println(String(indexPath.row) + " " + cell.nameLabel.text!)
return cell
}
}
In the custom cell class there is nothing special. Just a few outlets to the labels.
Here is a screen of the storyboard:
Storyboard
Can anyone please help me finding out what is going on here? I can't find the reason why the debug log can output the contents of a cell, but the device is not able to render them.
You should change the logic of your code. If the PickerCell comes up just call reloadData() and reload everything in the tableview. If the amount of rows you have is small this won’t be an issue and it’s not an expensive operation as you are not doing any heavy calculating during display.
If you need to update only a single cell because of changes you made in the PickerCell then you should be calling reloadRowsAtIndexPaths:withRowAnimation: with the indexPath of the cell to be updated.
Your issue is with your subclass WOSArticleCell. Have you implemented prepareForUse()? If you have, are you setting any properties to nil?
UITableViewCell Class Reference
Discussion
If a UITableViewCell object is reusable—that is, it has a reuse
identifier—this method is invoked just before the object is returned
from the UITableView method dequeueReusableCellWithIdentifier:. For
performance reasons, you should only reset attributes of the cell that
are not related to content, for example, alpha, editing, and selection
state. The table view's delegate in tableView:cellForRowAtIndexPath:
should always reset all content when reusing a cell. If the cell
object does not have an associated reuse identifier, this method is
not called. If you override this method, you must be sure to invoke
the superclass implementation.
Bit of a weird one i can't seem to understand so i have a tableview control in a viewcontroller and within the tableviewcell i have a button which is using a delegate.
So when the button is clicked it will change the tag number of the cell and also change the image of the button based on the tag of the cell in the tableview.
But the problem i'm having is that when you select a button in a row i.e. the first one it seems to be running the function to change the image for each item in a section almost. I.e choosing the 5th item will update every 5th button in a cell to the selected image which is weird. Since it's almost like the tableview is being split up to sections of 5.
Can anyone help prevent this behaviour so it only changes the icon for the button in the cell which has been pressed.
Below are the functions that i've used and a link to a video on dropbox showing the behaviour https://www.dropbox.com/s/a4aasti78872w6j/Help.mov?dl=0
Delegate
protocol StoryTableViewCellDelegate: class {
func didBookmarkItem(cell: StoryTableViewCell, sender: AnyObject)
}
Function for Delegate
#IBAction func bookmarkButtonDidTouch(sender: AnyObject) {
bookmarkButton.animation = "pop"
bookmarkButton.curve = "easeOut"
bookmarkButton.duration = 0.5
bookmarkButton.damping = 0.4
bookmarkButton.velocity = 0.4
bookmarkButton.animate()
// The delegate which will handle bookmarking items
delegate?.didBookmarkItem(self, sender: sender)
}
Function being used in tableview class
// MARK: StoryTableViewDelegate
func didBookmarkItem(cell: StoryTableViewCell, sender: AnyObject) {
// TODO: Implement bookmark functionality
switch cell.bookmarkButton.tag {
case 0:
cell.bookmarkButton.setImage(UIImage(named: "Bookmark-Selected"), forState: UIControlState.Normal)
cell.bookmarkButton.tag = 1
case 1:
cell.bookmarkButton.setImage(UIImage(named: "Bookmark-Not-Selected"), forState: UIControlState.Normal)
cell.bookmarkButton.tag = 0
default:
break
}
}
The reason is, you are probable creating a cell using :
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("cellID")
...
like you should do. However dequeueReusableCellWithIdentifier re-uses a cell, so if you have changed anything in a cell (like adding buttons), those buttons will still be in that recycled cell.
So you must set the book mark status in your cellForRowAtIndexPath for each cell.
I once had a similar problem when adding buttons to a cell, and when scrolling the cells automatically had extra buttons. So the first thing I did when re-using a cell was remove all buttons.
Edit sample code
in your
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath)
you have to add code for setting the button to the desired state, it will be something similar to the code you're using in didBookMarkItem :
switch myProperty {
case 0:
cell.bookmarkButton.setImage(UIImage(named: "Bookmark-Selected"), forState: UIControlState.Normal)
cell.bookmarkButton.tag = 1
case 1:
cell.bookmarkButton.setImage(UIImage(named: "Bookmark-Not-Selected"), forState: UIControlState.Normal)
cell.bookmarkButton.tag = 0
default:
break
}
You'll need a myProperty variable of course, which you should change in your didBookMarkItem as well
As others have said, it's due to table cell reuse. You want your tableView(_:cellForRowAtIndexPath:) method to always update the cell state from your model. Your bookmark state should be a property of your model. When the bookmark button state for a cell is changed by the user, the new state should be reflected in your model. If you do these things, your table cell state will always be correct. If you don't already, it's nice to always define a custom UITableViewCell class that contains outlets for all of the views and controls within your table view cell (your bookmark button would have an outlet.) Also, within your custom cell class, when you capture the button selection, you can call back to the controller either via a delegate (as you are doing), or a "bookmarkChanged" handler (closure) defined on the cell. I prefer the closure method. If you would like to see an working example of this, let me know.
Also, nix the tag. You don't need the tag to keep track of your bookmark button selection state, unless there's more to it than you have shown/described. If you follow the approach I described, it's taken care of.
Table view cells are reused. Once you select a cell and change its tag number and scroll the selected cell out of the table view, it will be used again to show a row at the index path of the new row that appears. And since its tag represents that of a selected cell it is displayed as highlighted.
Try to look up about cell reuse in table views.
You need to change your approach about determining which cell is to be displayed as selected. Add it as a property in your data source and based on that set the bookmark as selected or not selected.