I have a UITableView that has about 30 items. Here's an overview of how my tableview works: In order to enable infinite scrolling and a small memory size, I calculate the scrolling direction, speed, and I remove the top 10 items and add 10 items to the bottom (the same goes for scrolling up the other way). If I were to scroll to an item, the indexPath.row stays at that same item when I attempt to reloadData() with a new set of 30 items.
I have tried creating my own index to use, but it has a lot facets to it that would make it pretty complicated. I'm looking to see if I can just reset indexPath.row.
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
item = items[indexPath.row]
}
Sometimes, I would like to jump to another set of items that is a few pages down. So, I then replace the current array of items with a new 30 items. However, when I have already scrolled down a little (let's say I'm on the 15th cell), and I then jump to a new set of 30 items, the very first cell to show in tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell is the 15th cell. indexPath.row = 15... Why is indexPath.row not updating to 0? Is there a way to reset indexPath.row to 0 when I fill my array with a new set of items and call reloadData()?
Apparently, manually setting the indexPath is not possible. Instead, I just scroll the tableView to the top to ensure that it starts at the very first element.
tableView.scroll(to: .top, animated: false)
Related
In UITableView, when tapping and holding a cell and (without releasing this cell) switching to another screen in tab bar and returning to the initial one, the cell remains highlighted (not selected) and if tapping on another cell, the first one gets selected.
Upon tapping and holding the first cell, tableView(_ tableView: UITableView, didHighlightRowAt indexPath: IndexPath) is called for the first cell. So far it is how it should be.
Upon tapping on another cell (after returning to the screen), tableView(_ tableView: UITableView, didUnhighlightRowAt indexPath: IndexPath) is called for the first cell. And then all methods for selection for the first cell.
Is there a way to remove this behaviour? And upon returning to the screen have no highlighted cells.
cell.setHighlighted(false, animated: false) doesn't work. Yes, it removes highlighting, but selection methods are again called for the first cell.
Have you tried to implement shouldHighlightRowAt and return false?
From the docs for tableView(_:shouldHighlightRowAt:):
Asks the delegate if the specified row should be highlighted.
I'm getting weird behaviour in my TableView
I turned isUserInteractionEnabled on one of my section headers because I need to put a collectionView in it. Before I did anything I noticed that when I tap on that header view (it is a UITableViewCell) it triggers the didSelectRowAt method with the index of a first cell in that section (right below the header). Does anybody know what causes that behaviour and how to turn it off?
Your header sections are part of your UITableView.
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath){
}
In this method indexPath return rows and section, indexPath.section
-> returns section of UitableView, you have tapped and indexPath.row -> returns down of that particular section, tapped.
So this function is going to get called no matter what you do. You
need to override the table view's gesture to avoid this.
I am working on a ViewController with a TableView populated with dynamic cells from a prototype nib. I have run into a dead-end trying to recreate certain a cell-expanding animation.
My goal:
When a cell is selected, the selected cell should "expand" (grow in height to twice it's starting size) while at the same time creating space between the cell directly above and below the selected cell.
I've found an example of EXACTLY the asethetic I am looking for in the app "Things". Below are two screenshots showing the table before and and after a cell is selected:
Screenshot of table BEFORE expansion
Screenshot of table AFTER expansion
The best way I can describe the desired animation is the UITableView version of "the parting of the Red Sea". When a cell is selected, the surrounding cells give way lending the selected cell more room.. and the user's focus.
What I've tried:
I found Simon Lee's method answering a similar question and implemented it into my project. And although it animates the row-height change perfectly, it only pushes the adjacent cells on one side of the selected cell. (ie: if the cell at index 4 is selected, all the cells from index 5+ move down but those from index 0-3 stay static. Thereby not achieving the look I'm seeking.)
Using that method, the relevant sections of my code looked something like:
var cellHeight: CGFloat = 72
var selectedCell: IndexPath?
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
if indexPath == selectedCell {
return cellHeight * 2
} else {
return cellHeight
}
}
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
selectedCell = indexPath
tableView.beginUpdates()
tableView.endUpdates()
}
func tableView(_ tableView: UITableView, didDeselectRowAt indexPath: IndexPath) {
selectedCell = nil
tableView.beginUpdates()
tableView.endUpdates()
}
Because that didn't result in my desired animation, I tried insertRows:at:with: to insert 2 empty cells (1 above and 1 below the selected row) -- then deleteRows:at:with: to remove them upon deselecting the cell. This ultimately made for a better looking animation, and looked closer to the "Things" example I'm shooting for. However this made the table overly complicated because by adding and removing cells each time a row is selected, it would change the index of the other cells making it frustrating to predict which cells would have what index at any given time.
A possible solution idea?
After working on this for a couple of days the only other way I could think to accomplish what I want is to somehow scroll the table slightly at the same time that the selected cell's height it changed.. so that as the cell expands (moving the following cells downward) it would make the previous cells appear to move upward. I'm hesitant to try this because it feels like a hack, there should be a better way to accomplish this.
ANY help would be thoroughly appreciated! I've been pulling my hair out at an alarming rate. Thank you to anyone who can share their knowledge.
I have dynamic cell height in my tableView
tableView.rowHeight = UITableViewAutomaticDimension
tableView.estimatedRowHeight = 100
I want to do same as whatsapp app (pagination), i want to load 25 by 25 row so when user scroll at top, i want to load new data but i want to keep same position of scroll, here is what i did
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if isMore && scrollView.contentOffset.y == 0 {
loadMore() // function that add new data in my model
self.tableView.reloadData()
}
}
The problem that i have is after i reach top of my tableview it call reloadData but the tableView scroll to UP
I tester some other solution like this:
var cellHeights: [IndexPath : CGFloat] = [:]
func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
cellHeights[indexPath] = cell.frame.size.height
}
func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
guard let height = cellHeights[indexPath] else { return 70.0 }
return height
}
But still not working
If you are reloading the table to add more data , then after reload call below function to retain the scroll position.
tableview.scrollToRow(at: indexPath, at: .middle, animated: true)
here indexPath is the indexPath of the last cell before reload.
In tableView:cellForRowAt when you detect indexPath is getting close to the last element (when indexPath.row is getting close to yourArray.count), query for more items. When you have them, add them to your data source (the array, or whatever it is, where you have all the objects represented in the table) and reload the table view. The table view should display the new items and the user can continue scrolling without doing anything special.
You shouldn't wait until tableView:cellForRowAt is called for the last cell, as the user will have to wait if you need to call a server to fetch more items. Whatsapp's scroll is fast because they download the items well before you scroll to the last elements (some time ago it did stop at the end, but now they are probably fetching new items way earlier).
Keep in mind that 25 items might be too few, it the network is slow the user might scroll through the items you have before more items to display and will have to wait, which is not a good user experience. Simulate a slow network connection and see if 25 items are enough to scroll through while your app contacts the server (depends on network speed, request and response sizes, how fast the server answers your request, etc.).
I faced the same problem in a messaging App. Here's how I solved it:
Assigned an unique messageId to every message in datasource array.
In cellForRow:, I save that messageId of very first row in a variable called messageIdFirst.
if(indexPath.row == 0){
messageIdFirst = message.id!
}
In loadMore() method, I check which current indexpath row have the same messageId in now updated datasource array.
if(message.id == messageIdFirst){
previousTopIndexPath = i
}
,where i being that index in datasource array which have the same messageId.
Now, I scroll to that previousTopIndexPath like this:
tableview.scrollToRow(at: previousTopIndexPath, at: .middle, animated: true)
Note 1: As this was not working efficiently in UITableView, I end up using UICollectionView with the same solution.
Note 2: While this does work smoothly, I know there must exist a cleaner way to do this.
I have a UITableView that has multi selection enabled. I have been using the "selection" to actually change the height of the rows, showing extra detail when "selected". E.g.
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
self.tableView.beginUpdates()
self.tableView.endUpdates()
}
func tableView(tableView: UITableView, didDeselectRowAtIndexPath indexPath: NSIndexPath) {
self.tableView.beginUpdates()
self.tableView.endUpdates()
}
func tableView(tableView: UITableView, heightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
return (self.tableView.indexPathsForSelectedRows?.contains(indexPath) ?? false) ? 200 : 92
}
This seems to work pretty well. Until I start doing any swipes actions. When I add some swipe actions, the swipe action seems to clear all of my selections. I actually wanted to deselect the one I was swiping, so it would shrink back down. But the clearing of all my selections doesn't seem to trigger any of the normal delegate callbacks. Even though I have allowsMultipleSelectionDuringEditing set to true.
Is there a way to do this? Should I skip (ab)using the selection state as a way to indicate whether the row is showing details with a different height or not? Or is there a way to use it in conjunction with the behavior of the swipes being done in "edit mode" and clearing all of my selections?
The best way is using NSArray to store indexPath of selected cells, and base on saved indexPath you can check and do anything you want. another bug may happened in your code is: What happened in the case user make scroll on tableview? Does cell will reuse and lose select state? New cell reuse the old cell with 200 height will has wrong height?