UIcollection view does not scroll?
<p>I have added a <code>UICollectionView</code> in my app. I have given its constraints like leading, trailing, top &amp; some fixed height of the collection view. It is showing all items. But I am not able to scroll it. Please tell what is the issue?</p>

<pre><code>   func numberOfSectionsInCollectionView(collectionView: UICollectionView) -&gt; Int {

        return 1
    }
    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -&gt; Int {

        print("count is \(arr_collection.count)")
        return arr_collection.count
    }
    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -&gt; UICollectionViewCell {

        let identifier="col_cell"
        let cell:CollectionCell
        cell=collectionView.dequeueReusableCellWithReuseIdentifier(identifier, forIndexPath: indexPath ) as! CollectionCell
        cell.img_cell.image=UIImage(named: arr_collection[indexPath.row])
        print("arr collection is \(arr_collection[indexPath.row])")
        return cell
    }
</code></pre>