How to insert Cell in UICollectionVIew Programmatically? - ios

Question

I have a UICollectionView and it works fine, but I want to add a few UICollectionViewCells items programmatically into the collection view.
So how can I achieve this?
To further clarify: when I say programmatically I mean inserting a cell during runtime, when an action is fired, not when the app is loaded (using the viewDidLoad method). I know when the model is updated and the call is made to UICollectionView in the insertItemsAtIndexPaths: method. It should create a new cells, but it's not doing that, it's throwing an error.

Answer 1

...By referring to UICollectionView documentation
You can accomplish:
Inserting, Deleting, and Moving Sections and Items To insert, delete,
or move a single section or item, follow these steps:
Update the data in your data source object.
Call the appropriate method of the collection view to insert or delete the section or item.
It is critical that you update your data source before notifying the
collection view of any changes. The collection view methods assume
that your data source contains the currently correct data. If it does
not, the collection view might receive the wrong set of items from
your data source or ask for items that are not there and crash your
app. When you add, delete, or move a single item programmatically, the
collection view’s methods automatically create animations to reflect
the changes. If you want to animate multiple changes together, though,
you must perform all insert, delete, or move calls inside a block and
pass that block to the performBatchUpdates:completion: method. The
batch update process then animates all of your changes at the same
time and you can freely mix calls to insert, delete, or move items
within the same block.
From your Question: you can for example register A gesture Recognizer, and Insert a NEW cell by
doing the following:
in
// in .h
#property (nonatomic, strong) NSMutableArray *data;
// in .m
#synthesize data
//
- (void)ViewDidLoad{
//....
myCollectonView.dataSource = self;
myCollectionView.delegate = self;
data = [[NSMutableArray alloc] initWithObjects:#"0",#"1", #"2" #"3", #"4",
#"5",#"6", #"7", #"8", #"9",
#"10", #"11", #"12", #"13",
#"14", #"15", nil];
UISwipeGestureRecognizer *swipeDown =
[[UISwipeGestureRecognizer alloc]
initWithTarget:self action:#selector(addNewCell:)];
swipeDown.direction = UISwipeGestureRecognizerDirectionDown;
[self.view addGestureRecognizer:swipeDown];
//..
}
-(void)addNewCell:(UISwipeGestureRecognizer *)downGesture {
NSArray *newData = [[NSArray alloc] initWithObjects:#"otherData", nil];
[self.myCollectionView performBatchUpdates:^{
int resultsSize = [self.data count]; //data is the previous array of data
[self.data addObjectsFromArray:newData];
NSMutableArray *arrayWithIndexPaths = [NSMutableArray array];
for (int i = resultsSize; i < resultsSize + newData.count; i++) {
[arrayWithIndexPaths addObject:[NSIndexPath indexPathForRow:i
inSection:0]];
}
[self.myCollectionView insertItemsAtIndexPaths:arrayWithIndexPaths];
} completion:nil];
}

Answer 2

If you are inserting multiple items into UICollectionView, you can use performBatchUpdates:
[self.collectionView performBatchUpdates:^{
// Insert the cut/copy items into data source as well as collection view
for (id item in self.selectedItems) {
// update your data source array
[self.images insertObject:item atIndex:indexPath.row];
[self.collectionView insertItemsAtIndexPaths:
[NSArray arrayWithObject:indexPath]];
}
} completion:nil];

Answer 3

– insertItemsAtIndexPaths: does the job

Answer 4

Here is how to insert an item in Swift 3 :
let indexPath = IndexPath(row:index, section: 0) //at some index
self.collectionView.insertItems(at: [indexPath])
You must first update your data.