UICollectionView with UICollectionFlowLayout not displaying cells in the right location - ios

Question

I have a UICollectionView in a test project that I created which does not use Interface Builder. When I run the app the test views that I give to the collection view, via the datasource, are displayed in the the top right corner around (0,0). And I cannot for the life of me figure out why. I have tried adding constraints to the cell's content view. I have also tried messing with the item insets delegate function, but that does not seem to make a difference. Am I missing something?
Here is the code for the test view controller.
#import "TestViewViewController.h"
#interface TestViewViewController () <UICollectionViewDelegateFlowLayout, UICollectionViewDataSource>
#property (strong, nonatomic) UICollectionView *collectionView;
#property (strong, nonatomic) UICollectionViewFlowLayout *flowLayout;
#property (strong, nonatomic) NSMutableArray *testViews;
#end
#implementation TestViewViewController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (void)loadView {
self.view = [[UIView alloc] init];
self.view.backgroundColor = [UIColor whiteColor];
self.flowLayout = [[UICollectionViewFlowLayout alloc] init];
self.testViews = [[NSMutableArray alloc] init];
UIView *testView = [[UIView alloc] init];
testView.backgroundColor = [UIColor blueColor];
testView.translatesAutoresizingMaskIntoConstraints = NO;
UILabel *testLabel = [[UILabel alloc] init];
testLabel.translatesAutoresizingMaskIntoConstraints = NO;
testLabel.text = #"I hate collection views.";
[testView addSubview:testLabel];
testView = [[UIView alloc] init];
testView.backgroundColor = [UIColor redColor];
testView.translatesAutoresizingMaskIntoConstraints = NO;
testLabel = [[UILabel alloc] init];
testLabel.translatesAutoresizingMaskIntoConstraints = NO;
testLabel.text = #"I really do.";
[testView addSubview:testLabel];
self.collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:self.flowLayout];
self.collectionView.translatesAutoresizingMaskIntoConstraints = NO;
self.collectionView.delegate = self;
self.collectionView.dataSource = self;
self.collectionView.backgroundColor = [UIColor grayColor];
[self.view addSubview:self.collectionView];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"MyCell"];
NSDictionary *views = #{#"collectionView": self.collectionView};
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[collectionView]|" options:0 metrics:nil views:views]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[collectionView]|" options:0 metrics:nil views:views]];
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
}
#pragma mark - UICollectionView Datasource
- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section {
return self.testViews.count;
}
- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView {
return 1;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [cv dequeueReusableCellWithReuseIdentifier:#"MyCell" forIndexPath:indexPath];
NSLog(#"%i", self.testViews.count);
[cell.contentView addSubview: self.testViews[indexPath.row]];
return cell;
}
#pragma mark – UICollectionViewDelegateFlowLayout
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
// UIView *statView = self.testViews[indexPath.row];
return CGSizeMake(100.0, 100.0);
}
#end

Answer 1

For openers the CGRectZero macro is the equivalent of CGRectMake(0, 0, 0, 0). It would seem that you'd be in trouble with a definition of the space in which the collection view was to be drawn and the CGRectZero origin of 0,0 would put it in the upper left corner of the view. I tried creating an app with your code - and finally got something to show up when I got the code for loadView to look like this:
- (void) loadView
{
self.view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
self.view.backgroundColor = [UIColor whiteColor];
self.flowLayout = [[UICollectionViewFlowLayout alloc] init];
self.testViews = [[NSMutableArray alloc] init];
UIView* testView = [[UIView alloc] initWithFrame:CGRectMake(0, 50, 320, 80)];
testView.backgroundColor = [UIColor blueColor];
testView.translatesAutoresizingMaskIntoConstraints = NO;
UILabel* testLabel = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 320, 80)];
testLabel.translatesAutoresizingMaskIntoConstraints = NO;
testLabel.text = #"I hate collection views.";
[testView addSubview:testLabel];
[self.testViews addObject:testView];
self.collectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 100, 320, 320) collectionViewLayout:self.flowLayout];
self.collectionView.translatesAutoresizingMaskIntoConstraints = NO;
self.collectionView.delegate = self;
self.collectionView.dataSource = self;
self.collectionView.backgroundColor = [UIColor grayColor];
[self.view addSubview:self.collectionView];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"MyCell"];
}
The difference being that objects were created with a frame size - that views were added into views and so on.
My thought is that you'd be better off creating your UICollectionViewin a XIB - setting all the parameters there and also creating a subclass for UICollectionViewCell to be able to do more with the contents of the cells as need be. There's a whole lot more to be done to make this a usable UICollectionView with an arbitrary number of cells, but I have to say, the UICollectionView is not an easy object to deal with - so I sympathize with you as you come up the learning curve.