In Objective C UITableVIew how to retain scroll position after calling reload
While selecting a cell I call reload function of the UITableView but after reload I want the scroll to maintain its position (i.e, Position where the cell was tapped)
You can use reloadRowsAtIndexPaths:withRowAnimation: instead of reloadData.
You could do something like this.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
[tableView reloadRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}
Also if you want to scroll to some particular position, you can use this.
[tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionNone animated:YES];
Two lines and you get the desired result:
NSArray *indexPaths = tableView.indexPathsForVisibleRows;
[tableView reloadRowsAtIndexPaths:indexPathswithRowAnimation:UITableViewRowAnimationNone];'
Related
So it's easy to select a row that is currently in the UITableView. For example, to select the first row:
[self.tableView selectRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]
animated:YES
scrollPosition:UITableViewScrollPositionNone];
Say that I have an array that is the data source for the table and the array count is greater than the number of cells displayed in the tableview. How can I get the UITableView to scroll to an index from the array that is beyond what is currently being displayed in the tableview?
All I am trying to do is to replicate programmatically what a user would do with their index finger as they scroll down the table.
My specific table displays 9 rows. My array has 20+ items. As the UIViewController loads, it retrieves the row number that should be selected (from an integer stored in NSUserDefaults). But I find that it will only scroll to the correct array position if that integer value is between 0 and 8. If it is 9 or greater, nothing happens, and I can't figure out how to make it respond to this. I've looked at all the UITableViewDelegate methods and none seems to address this.
What I've been doing to scroll and select a specific row is this (example arbitrarily selecting row 11):
[self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:11 inSection:0]
atScrollPosition:UITableViewScrollPositionTop
animated:YES];
[self.tableView selectRowAtIndexPath:[NSIndexPath indexPathForRow:11 inSection:0]
animated:YES
scrollPosition:UITableViewScrollPositionTop];
Can anyone help me? I assume it isn't difficult, but I'm stuck.
Thanks!
Your cells that are off the screen ain't selecting because you are using reusable cells. The cells from the visible screen will be used later, it isn't that all 100 cells are cached and each cell is responsible for each row. What it means is that they could or couldn't have something in it already. For example, lets say you have cell for row 1. When it comes off the screen, in the next few cells it will be reused as cell 15 or something, and if it had selected properties, it will still have it. It is like a new job and you get a desk from the developer before you - you could have desk with his trash, but it could also be clean.
I wouldn't select them as you select them by method, but in if statement in your cellForRowAtIndexPath. Something along the lines (added comments):
- (UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"Cell";
// When using method with forIndexPath you don't have to check for nil because you will always get cell
MyTableCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier forIndexPath:indexPath];
MyObj *obj = [self.myArray objectAtIndex:indexPath.row];
cell.location.text = obj.location.location_description;
// other formatting, text display, image loading, etc.
if ([self.selectedObjects containsObject:obj]) {
// do some selecting stuff
} else {
// but don't forget to unselect because you can get already selected cell
}
return cell;
}
Edit: To select invisible cell, first scroll to it, then select:
[self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:YES];
[self.tableView selectRowAtIndexPath:indexPath animated:YES scrollPosition:UITableViewScrollPositionTop];
Try using UITableViewScrollPositionBottom instead of UITableViewScrollPositionNone
That is use this code
[self.tableView selectRowAtIndexPath:[NSIndexPath indexPathForRow:10 inSection:0]
animated:YES
scrollPosition:UITableViewScrollPositionBottom];
I figured this out. My code was running in viewDidLoad which is too early. I needed to move it to viewDidAppear. At least I know that I am not losing my mind.
I have a tableview in a scrollview in a popover. When the view is presented, the bottom cell in tableview is not visible to the user. If I select all of the cells then deselect the fist cell, the out of view cell is deselected too. Has anyone come across this behaviour before? If so, how to approach it?
Now your job is to find all the visible cells in the tableview and then apply select/deselect to it.
UITableView *tableView = self.tableView;
// Or however you get your table view
NSArray *paths = [tableView indexPathsForVisibleRows];
// For getting the cells themselves
NSMutableSet *visibleCells = [[NSMutableSet alloc] init];
for (NSIndexPath *path in paths)
{
[visibleCells addObject:[tableView cellForRowAtIndexPath:path]];
}
// Now visibleCells contains all of the cells you care about.
-(void) tableView:(UITableView *)tableView didDeselectRowAtIndexPath:
(NSIndexPath *)indexPath {
[tableView deselectRowAtIndexPath:indexPath animated:YES];
}
- (void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:
(NSIndexPath *)indexPath {
//stuff
//as last line:
[tableView deselectRowAtIndexPath:indexPath animated:YES];
}
For that matter, deselectRowAtIndexPath can be called from anywhere at any time you want the row to be deselected.
[self.myTableView deselectRowAtIndexPath:[self.myTableView
indexPathForSelectedRow] animated: YES];
If you are using dequeueReusableCellWithIdentifier: change your cellForRowAtIndexPath: to use dequeueReusableCellWithIdentifier:forIndexPath:
In a UITableView cells get reused. That means it only produces as many as absolutely needed. As soon as a new one is coming onto the screen, the last one is "recycled" instead of initialising a whole new instance.
This makes your application run faster. It also means that you have to undo any changes you made, when recycling.
Selection status is one of them. The UITableView should manage this automatically for you, if it is dequeued with the relevant indexPath. If not, it wouldn't know whether that specific cell should be selected.
What I have
1). Container has UITableView, which has two custom UITableViewCells.
2). Core Data has certain entity which has a text to be displayed at
UITableViewCell each time I get into the View.
What i am doing ?
1) I have chosen -viewWillAppear method which gets invoked each time the view is visible.
2) In -viewWillAppear, I retrieved the data from core data.
3) Retrieved particular cell from UITableView
NSUInteger idxArr[] ={2,0}; // 2 nd section, 0th Row.
NSIndexPath *cPath = [NSIndexPath indexPathWithIndexes:idxArr length:2];
myCell *tCell = (myCell *)[self.settings cellForRowAtIndexPath:cPath];
tCell.myLabel.text = rec.servername; // rec.servername is from DC.
When I checked in the lldb,
tCell was nil.
Questions:
1) It is the right way of getting the Cell ?
2) Or, By the time -viewWillAppear, does the UITableView not Ready ?
I am sure.
You should populate the cells by conforming to tableView dataSource protocol and then in your viewWillAppear you should call reloadData on your tableView.
After calling reloadData for tableview, We need to call -scrollToRowAtIndexPath: before getting cell from -cellForRowAtIndexPath:.
Because, As we are calling a row in section 2, it might not be in the visible area until we scroll. So, cellForRowAtIndexPath: returns nil.
Method -cellForRowAtIndexPath: shouldn't be called programically. It's a data source method for UITableView and it contain some cell reuse optimalizations. If you update the view after scrolling down and up -tableView:cellForRowAtIndexPath will be called again and your changes won't be visible.
If you want to update specific cell you should update make changes in:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
YourCell *cell = [tableView dequeueReusableCellWithIdentifier:#"CellId" forIndexPath:indexPath];
YourData *data = //Get your data here
if (data.isReady) {
cell.tf.text = data[indexPath.row].text;
} else {
cell.tf.text = #"Not ready yet. Need to reload this cell later";
}
return cell;
}
And then call method below when you finish fetch your data.
[self.tableView reloadRowsAtIndexPaths:(NSArray *) withRowAnimation:UITableViewRowAnimationFade];
If you want to reload whole tableView (usually it's not slow) as #salaman140 says you can call [self.tableView reloadData] to update all visible cells.
If I were you I wouldn't use:
NSUInteger idxArr[] ={2,0}; // 2 nd section, 0th Row.
NSIndexPath *cPath = [NSIndexPath indexPathWithIndexes:idxArr length:2];
I would (is much more clear):
NSIndexPath *cPath = [NSIndexPath indexPathForRow:0 inSection:2];
I have an app in which I have a UITableview with custom cells and headers. The cells have an inputView so when selected they become first responder and allow the user to input data.
I want to be able to update the visible TableViewCell and header information on the fly while the user is changing it.. easy, just call [tableview reloadData]; ..
Unfortunately this causes the inputview to resign first responder and hide itself.
Is there any way that I can get a reference to the cell itself inside the UITableview so that I can just change the text property? (cellForRow:atIndexPath: returns a new object with the same properties so doesn't work) It seems like the only easy solution may be to store a reference the cells in a dictionary each time a cell is populated, not really the ideal solution.
cellForRowAtIndexPath is literally just
-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
CustomCell *orderCell;
static NSString *productCellIdentifier = #"ImageDetailCellIdentifier";
orderCell = [self.tableView dequeueReusableCellWithIdentifier:productCellIdentifier forIndexPath:indexPath];
//set a bunch of properties orderCell.blah
return orderCell;
}
According to UITableView documentation, -cellForRowAtIndexPath: returns an object representing a cell of the table or nil if the cell is not visible or indexPath is out of range.
That is also how I remember it. I don't think your observation is correct that it returns a new object. If the cell is visible you will get hold of it.
[tableView beginUpdates];
[tableView reloadRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationFade]; ///as your choice in animation
[tableView endUpdates];
or else
[tableView beginUpdates];
// do some work what ever u need
[tableView endUpdates];
For reloading specific rows, you can use
- (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation;
For example,
NSIndexPath* indexPath = [NSIndexPath indexPathForRow:2 inSection:1];
NSArray* indexArray = [NSArray arrayWithObject:indexPath];
[self.tableView beginUpdates];
[self.tableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationFade];
[self.tableView endUpdates];
i seem to be having some difficulty trying to access a particular cell, i just need to change one of its objects when i select it in the tableview. There must be a way more efficient way than just calling reloadData all over again. Because thats the only way i could make a table cell look different, by rebuilding it when i select on one. Thanks for all the help :)
[self updatePreferences];
[tableView reloadData];
This is all i have atm on the method where it handles the interaction with table cells.
Use the following code.To reload a single cell.
NSArray *array = [NSArray arrayWithObject:[NSIndexPath indexPathForRow:row inSection:section]];
[self.tableView reloadRowsAtIndexPaths:array withRowAnimation:UITableViewRowAnimationNone];
You could also make the cell a custom one and add a method to it like update or refresh.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
CustomCell *cell = [tableView cellForRowAtIndexPath:indexPath];
[cell refresh];
}