Overlay a static UIButton onto a UICollectionView - ios

Question

I have a UICollectionView that has an array of UICollectionViewCell each cell takes up 80% of the view.
I want to add a static UIButton onto the screen that scrolls to the next cell every time it is pressed, I will have to add the button subview onto the Parent view and not the UICollectionView for it to be static.
My questions are : how do I add the overlay onto the main view and how do I scroll the view programmatically with the press of the button?
Where I implemented my collection view
#interface EvaluationViewController () <UICollectionViewDataSource, UICollectionViewDelegate>
#property (weak, nonatomic) IBOutlet UIBarButtonItem *cancelButton;
#property (nonatomic, strong) DBManager* dbManager;
#end
#implementation EvaluationViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.dbManager = [[DBManager alloc] initWithDatabaseFilename:#"emokitDb.sqlite"];
NSLog(#"self.dbManager %#",self.dbManager.documentsDirectory);
[self loadProjectWithId:1];
}
- (IBAction)cancelButton:(id)sender {
[self dismissViewControllerAnimated:YES completion:nil];
}
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return 4;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
Screen * screen = [self.project.screens objectAtIndex:indexPath.row];
static NSString * cellIdentifier = #"EvaluationCell";
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
return cell;
}
-(void)loadProjectWithId:(int)projectId {
}
#end

Answer 1

It is quite easy:
You can add the button like that:
And you have to give a target to the button to move collectionView contentOffset...
- (void)viewDidLoad
{
[super viewDidLoad];
self.dbManager = [[DBManager alloc] initWithDatabaseFilename:#"emokitDb.sqlite"];
NSLog(#"self.dbManager %#",self.dbManager.documentsDirectory);
[self loadProjectWithId:1];
UIButton * button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
button.frame = CGRectMake(910, 400 , 100, 100);
button.backgroundColor =[UIColor blackColor];
[self.collectionView.superview addSubview:button];
[button addTarget:self action:#selector(changeContentOffset:) forControlEvents:UIControlEventTouchUpInside];
}
Then in the selector you have to implement a method to change contentOffset
- (IBAction)changeContentOffset:(id)sender {
[self.collectionView setContentOffset:CGPointMake(nextCellXValue, 0) animated:YES]
}