How to recycle background view of UICollectionViewCell or UITableViewCell - ios

I am creating a new background view each time a new cell is requested as follows:
-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"MyCell" forIndexPath:indexPath];
...
cell.backgroundView = [[MyCellBackgroundView alloc] initWithFrame:CGRectZero];
return cell;
}
Should I worry about so may instances being alloc'ed and dealloc'ed?

UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"MyCell" forIndexPath:indexPath];
This line of code handles the alloc / init of each cell and their subviews for you. Memory management it taken care of at this point.
If you're still curios - while running the app, open the debug navigator and it will show you CPU and memory usage.

Related

black window in simulator -collection view

The code is a simple collection view with a bunch of images
I ran it and Xcode doesn't argue about anything but the simulator shows a black screen after running the app.
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return recipePhotos.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
static NSString *identifier =#"Cell";
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
// Configure the cell
UIImageView * recipeImageView = (UIImageView *)[cell viewWithTag:100];
recipeImageView.image=[UIImage imageNamed:[recipePhotos objectAtIndex:indexPath.row]];
return cell;
}
Check collection view datasource outlet, maybe it was not connected with your controller?
Check receipeImageView is not nil.
Did you register your UICollectionViewCell with identifier #"Cell"?
If you don't want black background, you have to set
collectionView.backgroundColor = [UIColor clearColor];
Then you must register the cell
UINib *cellNib = [UINib nibWithNibName:#"yournibname" bundle:nil];
[collectionView registerNib:cellNib forCellWithReuseIdentifier:#"cell"];
Both need to be implemented in viewDidLoad method

UICollectionView Assistance

I am in the process of creating an App to take care of Maintenance Planning for Harley Davidson enthusiasts.
The planned target is the iPad series at this point.
I wish do display a grid that shows detail for each fuel purchase. The following graphic hopefully shows what I am trying to achieve.
To get this, I’m using the UICollectionView as I don’t think there is another View that gives me what I am after.
The code below illustrates how I have done this – but I believe it’s a pretty chunky way of doing it:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
FuelCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
cell.backgroundColor = [UIColor lightTextColor];
cell.cellLabel.text = [NSString stringWithFormat:#" %# %# %# %#",self.fuelDetailsForSelectedBike[indexPath.row][0],self.fuelDetailsForSelectedBike[indexPath.row][1],self.fuelDetailsForSelectedBike[indexPath.row][2],self.fuelDetailsForSelectedBike[indexPath.row][3]];
return cell;
}
What I would prefer is have a cell for each piece of information but unsure how I would achieve this using the UICollectionView.
You already have created a custom cell FuelCollectionViewCell which is a good starting point.
Probably you have a prototype cell in your Storyboard with subclass FuelCollectionViewCell right?
In this cell, add 4 UILabel aligned in one row as your design and 'link' them to your subclass .h file with a simple drag+alt (as you've done with cellLabel).
And update your cellForItemAtIndexPath method with something like:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
FuelCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"Cell" forIndexPath:indexPath];
cell.backgroundColor = [UIColor lightTextColor];
cell.dateLabel.text = self.fuelDetailsForSelectedBike[indexPath.row][0];
cell.litresLabel.text = self.fuelDetailsForSelectedBike[indexPath.row][1];
cell.distanceLabel.text = self.fuelDetailsForSelectedBike[indexPath.row][2];
cell.costLabel.text = self.fuelDetailsForSelectedBike[indexPath.row][3];
return cell;
}

unable to load collection view cell

I am able to load the collection view but unable to load the cell.below is my code I'm using.
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = #"reuseCell";
[self.view_dashboard registerClass:[UICollectionViewCell class]
forCellWithReuseIdentifier:#"reuseCell"];
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
recipeImageView = (UIImageView *)[cell viewWithTag:100];
recipeImageView.image= [UIImage imageNamed:[dashBoard_img objectAtIndex:indexPath.row]];
return cell;
}
There doesn't seem to be anything particularly wrong with your code.
Loading a cell in a collection view requires more work than just this single method.
I would start explaining further, but I would just be reading the docs to you. Instead, have a read of the Apple Documentation for yourself.
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UICollectionView_class/index.html#//apple_ref/doc/uid/TP40012177-CH1-SW4

UICollectionViewCell Only Updates After Scrolling

I've got an issue with my UICollectionView where my cells are always initiated blank/in a default state with no data.
The data only appears in the cells after scrolling them in and out of view.
Code:
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"EquipmentCell";
APInventoryCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
if (!cell) cell = [[APInventoryCollectionViewCell alloc] init];
//set cell data...
cell.label.text = [arrayOfStrings objectAtIndex:indexPath.row];
return cell;
}
Your problem is that you probably set the arrayOfStrings somewhere in the viewDidLoad method of your view controller, the problem with that is that the collectionview datasource calls are done before that.
What you should do in your viewDidLoad method just call [collectionview reloadData]; an you will be fine

CollectionView Highlights incorrect Cell When Scrolling

I have a UICollectionView. When an user clicks a cell the colour of the cell changes to red. I have coded the above part and it works perfectly.
However, when I scroll below, other cells in the collection view has got highlighted with the colour red. I am sure that it hasn't been selected but only highlighted.
How can I solve this.
My code is as follows:
cellForItemAtIndexPath Method
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *CellIdentifier = #"cell";
ViewCell *vc = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
vc.vciv.image = [arrayOfImages objectAtIndex:indexPath.row];
return vc;
}
didSelectItemAtIndexPath Method
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
if([items containsObject:allItem[indexPath.row]] ){
UICollectionViewCell *c =[collectionView cellForItemAtIndexPath:indexPath];
c.backgroundColor = [UIColor clearColor];
} else {
UICollectionViewCell *c =[collectionView cellForItemAtIndexPath:indexPath];
c.backgroundColor = [UIColor redColor];
}
As the collection view cells get reused, you need to make sure a dequeued cell is not highlighted in the cellForItemAtIndexPath: method:
UICollectionViewCell *vc = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
vc.backgroundColor = [UIColor clearColor];
This code will clear the cell's background always when dequeuing. If you need to preserve the highlighting, you need to store the indexPaths of the cells that you want to have highlighted, and check for the current cell being in that list.
EDIT
It seems that your items variable is well suited to do that.
So you would do:
UICollectionViewCell *vc = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
vc.backgroundColor = [items containsObject:allItem[indexPath.row]] ? [UIColor redColor] : [UIColor clearColor];

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