UICollectionView单元内部加载，但未显示UICollectionView

Question

Seems cell is loaded internally but , UICollectionView does not appear .

CollectionViewCell.xib and CollectionResuableView.xib also be included in the project .

CollectionView is the remains of black.

Why it is not working? I have use Xcode 6 and use below code.

---

ViewController.h

#import <UIKit/UIKit.h>
#import "CollectionReusableView.h"
#import "CollectionViewCell.h"
@interface ViewController : UIViewController<UICollectionViewDelegate,UICollectionViewDataSource>

@property (weak, nonatomic) IBOutlet UICollectionView *collectionView;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self _setup];
}

- (void)_setup{
    self.collectionView.delegate = (id)self;
    self.collectionView.dataSource = (id)self;
     [self.collectionView registerNib:[UINib nibWithNibName:@"CollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"Cell"];
    [self.collectionView registerNib:[UINib nibWithNibName:@"CollectionReusableView" bundle:nil] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"Section"];
}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 3;
}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
        CollectionReusableView *sectionView = [self.collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"Section" forIndexPath:indexPath];
        sectionView.label.text = [NSString stringWithFormat:@"Section%ld", indexPath.section + 1];
        return sectionView;
    } else {
        return nil;
    }
}

- (NSInteger) collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 10;
}

- (CollectionViewCell *) collectionView:(UICollectionView *)collectionView
                          cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier: @"Cell" forIndexPath:indexPath];
    cell.label.text = [NSString stringWithFormat:@"Row: %li",(long)indexPath.row];
    NSLog(@"%@",[cell.label debugDescription]);
    return cell;
}
@end

NSLog(@"%@",[cell.label debugDescription]);

2014-11-11 14:54:46.899 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c54af0; frame = (58 14; 42 21); text = 'Row: 0'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c54c50>>
2014-11-11 14:54:46.900 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c58850; frame = (58 14; 42 21); text = 'Row: 1'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c589b0>>
2014-11-11 14:54:46.900 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c5c5c0; frame = (58 14; 42 21); text = 'Row: 2'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c5c720>>
2014-11-11 14:54:46.901 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c60360; frame = (58 14; 42 21); text = 'Row: 3'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c604c0>>
2014-11-11 14:54:46.901 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c64130; frame = (58 14; 42 21); text = 'Row: 4'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c64290>>
2014-11-11 14:54:46.902 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c67d20; frame = (58 14; 42 21); text = 'Row: 5'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c67e80>>
2014-11-11 14:54:46.902 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c6bac0; frame = (58 14; 42 21); text = 'Row: 6'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c6bc20>>
2014-11-11 14:54:46.903 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c6f8a0; frame = (58 14; 42 21); text = 'Row: 7'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c6fa00>>
2014-11-11 14:54:46.903 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c73610; frame = (58 14; 42 21); text = 'Row: 8'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c73770>>
2014-11-11 14:54:46.904 collectionViewSample[7242:1226917] <UILabel: 0x7fd492c771d0; frame = (58 14; 42 21); text = 'Row: 9'; opaque = NO; autoresize = RM+BM; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x7fd492c77330>>

Answer 1

Collectionview没有出现，所以我认为collectionview布局中存在问题，因此首先在您的viewcontroller中实现委托UICollectionViewDelegateFlowLayout并尝试添加一些collectionview的委托方法来检查它是否正确触发了它的委托，因此它将为您提供帮助。

Answer 2

In the two work days I spent searching for the cause of "black rectangle" for UICollectionView when all delegate methods etc. are working, I twice read every SO entry about "UICollectionView" and "black" and there are many still unanswered. Choosing this question as more recent: in IB/XIB, Storyboard, Attributes Inspector for the UICollectionView, scroll down to the View section, change Background from Default to another color, and rebuild.
I conclude it frequently happens that when first testing a UICollectionView to see if you can make it work, with a default Label (black text) and possibly default Image (possibly without yet assigning an actual image to it, or possibly of dark color or transparent) in the UICollectionViewCell, the simulator displays the black rectangle, so you conclude your new code is broken when problem is simple graphics.