My custom cell contains many ui elements. I found it very difficult to reuse cells.So i set the cell created to nil in the didEndDisplayingCell delegate method of table view. Is there any issue in doing so. will it hamper performance. This is my code
(void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
if ([tableView.indexPathsForVisibleRows indexOfObject:indexPath] == NSNotFound){
VBMerchantDealCell *cell = (VBMerchantDealCell *)[tableView cellForRowAtIndexPath:indexPath];
cell = nil;
}
}
Make use of the prepareToReuse method in your cell subclass. Here reset all the values to default and in the corresponding cellForRowAtIndexPath method set the appropriate values to cell.
And ya, not reusing the cell is an unnecessary performance overhead.
Yes, not reusing cells will be very bad for performance. Also using transparency in your cells is likely to affect performance (i.e. Scrolling). You can use instruments or the simulator to check for this: 'color blended layers' will color all non-opaque views as red.
Related
I have an UITableView with ±10 different UITableViewCells to display full information about an object (description cell, photos cell etc.). So when UITableView is loaded, I do not need UITableView cells to be reused. Wouldn't performance be better if I somehow store UITableViewCells and prevent cellForRowAtIndexPath from being called? If so, what is the way to achieve alike behaviour?
First of all, you can not prevent cellForRowAtIndexPath from being called if you are gonna use UITableView. It is a UITableViewDataSource function and it's not an optional one. Otherwise, you won't be able to populate your tableview.
What you can do is use switch case on indexpath.row in cellForRowAtIndexPath and return necessary cell.
You could try by increasing prototype cell in Storyboard. each cell assign new cell identifier and you need to keep array of identifier matching their index with storyboard.
Your cellForRowAtIndexpath will reduced to:
- (UITableViewCell *)tableView:(UITableView *)tableView1 cellForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [tableView1 dequeueReusableCellWithIdentifier:[cellIdArray objectAtIndex:indexPath.row] forIndexPath:indexPath];
return cell;
}
Note: cellForRowAtIndexpath method will always called. In above case you can put your data in storyboard itself.
Check similar case at https://www.appcoda.com/sidebar-menu-swift/
I have a list of custom cells in my tableview and as I scroll everything appears to fine and the cells appear to be in the same order. I have some functionality with my cells - as i select a cell (and it dynamically expands)the background color changes and a few other custom cell properties. Once I do this and then I start scrolling, different cells that i haven't even touched before show up, selected(expanded) and the cell only updates when I select it manually to the correct data. I seem to see duplicates and all kinds of craziness.
I know there are LOTS of posts about this on here so far but for me, so far nothing has worked. Would like some input on what I could do to stop this ridiculous behavior.
I have posted some code to give you a better idea of what I am doing. I know that 'dequeueReusableCellWithIdentifier' is the culprit but don't know of an alternative.
As side notes, this is a tableview(its own xib) that is a child view of a large view (also a xib). I have also already registered the nib for the tableview.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
MyCustomCell *cell = [tableView dequeueReusableCellWithIdentifier:myIndentifier forIndexPath:indexPath];
if(self.currentSelectedIndex){
if(self.previousSelectedIndex){
//collapse cell
//configure cell in method(change background color etc)
}
else{
//expand cell
//configure cell in method(change background color etc)
}
}
}
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
self.currentSelectedIndex = indexPath;
[tableView beginUpdates];
if(self.currentSelectedIndex){
if(self.previousSelectedIndex && (self.previousSelectedIndex != self.currentSelectedIndex)){
[tableView reloadRowsAtIndexPaths:#[self.currentSelectedIndex, self.previousSelectedIndex] withRowAnimation:UITableViewRowAnimationAutomatic];
}
else{
[tableView reloadRowsAtIndexPaths:#[self.currentSelectedIndex] withRowAnimation:UITableViewRowAnimationAutomatic];
}
}
[tableView endUpdates];
if(self.previousSelectedIndex == self.currentSelectedIndex){
self.previousSelectedIndex = nil;
}
else{
self.previousSelectedIndex = self.currentSelectedIndex;
}
}
What can I do or how would i make sure that nothing else in the list 'seems' to be selected(expanded) or prevent from appearing to see duplicates as i scroll? I already keep track of my current and last selected index(as shown in the code) so I suppose that I could use that somehow?
Dequeued Cells are Reused
Know that cells are re-used, so that the appearance of a UITableViewCell is persistent for the entire life of that cell.
This means that if you do not explicitly reset all the presentation view of your cell, and just returning it unchanged in cellForRowAtIndexPath, what you are returning may be a currently selected (or deselected) cached cell.
A possible location to reset a table cell is prepareForReuse.
Design note:
How are you maintaining self.currentSelectedIndex and self.previousSelectedIndex? This is typically quite dangerous, since you are attempting to replicate the UITableView behavior. It is for example, unlikely to work with multiple selection. Setting an active selection is unlikely handle situations when the OS didDeselectRowAtIndexPath, as a result of a keyboard dismissal for example.
Hello guys i think almost everyone who is in ios development may come across the issue of reuse of the UITableCell by using following code line.
RZRestaurantListingCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
I have search lot about this but not getting any desire answer so please help me out in this case.
I have the same issue as most of iPhone developer having after reusing the cell.
I have the UIProgressView inside my cell and one button is there for downloading the video and i am showing the progress there in progress view how much is left.
So Now what i have problem is when i have more data and going out of the screen at that time i am press the download button on very first row of the UITableviewCell then i am scrolling down so the progress also shown in bottom random one cell so the UI changes in two cell rather then one.
You need to implement -prepareForReuse method in your custom cell class and set all cell properties to default value.
- (void)prepareForReuse
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.
Refer here for more, https://developer.apple.com/library/ios/documentation/UIKit/Reference/UITableViewCell_Class/#//apple_ref/occ/instm/UITableViewCell/prepareForReuse
You need to assign a progress value inside the - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
RZRestaurantListingCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];
// If the cell is reused, the `-prepareForReuse:` of `UITableViewCell` will be called.
//!! Assign current progress value to this cell, otherwise, the progressBar.value may look like a random value.
//!! Because the current cell is reused from a disappeared cell.
cell.progressBar.value = ... ;
return cell;
}
The design may be complex, because the progress may be updated continuously when the cell is on the screen.
Use prepareforreuse method to clear content of cell before using it... e.g.
-(void)prepareForReuse
{
[super prepareForReuse];
self.textLabel.text = #"";
self.detailTextLabel.text = #"";
self.imageView.image = nil;
}
Hi i have been searching around to find a way to remove a static cell with animation but i have not found a solution to the problem.
I have also tried: [tableView deleteRowsAtIndexPaths:[self.taskArray objectAtIndex:indexPath.row] withRowAnimation:UITableViewRowAnimationFade];
but no success.
You need to hide cell before it is shown, in UITableViewDelegate's tableView:willDisplayCell:forRowAtIndexPath: method. This is the last method in your control where you can manipulate the cell display. It does not remove the space the cell takes, so another thing you can try is to set cell row's height to 0 using the tableView:heightForRowAtIndexPath: method of the same protocol.
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
UITableViewCell *cell = [super tableView:tableView cellForRowAtIndexPath:indexPath];
if (yourCell) {
return 0;
} else {
return [super tableView:tableView heightForRowAtIndexPath:indexPath];
}
}
As your tableview is static, you cannot use deleteRowsAtIndexPath. The best option would probably be to migrate your data into a dataSource method for the tableview.
If this is impossible, then this answer ("UITableView set to static cells. Is it possible to hide some of the cells programmatically?") gives that the best method is to use the third party library
StaticDataTableViewController 2.0 (https://github.com/xelvenone/StaticDataTableViewController).
Otherwise you have to use the somewhat hacky method of changing the row height to 0.
At my experiment I need to have reference to first UITableViewCell in tableView. By some action I need to set image and some other cell properties and to keep this state of this only cell even if the tableView will be scrolled. All of this properties can be potentially nulled via scrolling (and they actually are) because of reusing. For set this properties every time cell appears on screen, inside of `-cellForRowAtIndexpath' I tried to catch first cell using:
UITableViewCell *firstCell = (UITableViewCell *)[atableView cellForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];
but looks like this way I can only catch every next first cell on next scrollable "screen".
So, how can I get ref to first UITableView cell?
If I understand you correctly, you are trying to do something special if the cell at (0, 0) is about to be displayed, right? If that's the case, you can easily implement UITableViewDelegate's tableView:willDisplayCell:forRowAtIndexPath: method as follows:
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath) {
// Do something special
}
}
There is also a corresponding tableView:didEndDisplayingCell:forRowAtIndexPath: method if you need to undo things.
Hope it helps!
There is no "first" table view cell. The entire table view typically uses a single cell to improve performance.
You can change that, by implementing your own cell reuse system (search for reuse in the documentation). But generally the cell is the wrong place to store any data related to a specific index in the table view.