Does UICollectionViewCell have a viewWillAppear or something I can pass data to

Question

I have this in my view controller:

- (UICollectionViewCell *) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
     CellSubclass *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath];

     cell.dataObjects = data;

     return cell;
}

In my CellSubclass.m I have:

- (id) initWithFrame:(CGRect)frame
{
    // You can call initWithFrame: method here as our base constructor of the UIView super class
    self = [super initWithFrame:frame];

    if (self)
    {
        // call functions that need access to data but data is nil
    }

    return self;
}

So in the lifecycle of my view controller, the CellSubclass gets called immediately before the data is ready. Is there a function like viewWillAppear or something that I can pass the data too? How can I call a function from my view controller other than initWithFrame? Can I pass the data in other ways?

Thanks.

Solution 1

It sounds better to use your own configure method for cell in cellForItemAtIndexPath.

- (UICollectionViewCell *) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
     CellSubclass *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" 
                                                                    forIndexPath:indexPath];

     cell.dataObjects = fetchedMUtableArray[indexPath.row];

     [cell somethingConfiguringMethods];

     return cell;
}

Solution 2

UICollectionViewCell does not have something like that, but that is a subclass of UIView and that one has didMoveToSuperview. I use it in production for some specific cases, but anyway it helps for some fast debugging also.

https://developer.apple.com/documentation/uikit/uiview/1622433-didmovetosuperview

Solution 3

You should return the number of cells as 0 when you do not have any data to show. When you have the data ready just reload collection view.

In your datasource methods

- (NSInteger)collectionView:(UICollectionView *)collectionView
     numberOfItemsInSection:(NSInteger)section {
    if (self.collectionViewData)
        return self.collectionViewData.count; 
    else
        return 0;
}

Lets say you have an async network call and it has returned data. In the completion block just reload collection view.

-(void)fetchData {
    [httpClient fetchDataWithCompletionBlock:^(NSArray *data) {
        [self.collectionView reloadData];
    }];
}