cellForItemAtIndexPath,sizeForItemAtIndexPath,insetForSectionAtIndex未被调用iOS

我使用COllectionView在从Core database获取后显示图像.但是,除了numberOfItemsInSection& numberOfSectionsInCollectionView.代理和数据源设置正确.

单元的标识符是photoCell,类是JLTPhotoCell.

- (void)viewDidLoad
        {
            [super viewDidLoad];
            _thumbNails = [[NSArray alloc]init]; // its declared,don't worry about this
            _thumbNails = [[LADataModelController getSingleton] getAllSignatures];

            UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
            [layout setItemSize:( CGSizeMake(50,50))];
            [_collectionView setCollectionViewLayout:layout];
            self.collectionView.delegate = self;
            self.collectionView.datasource = self;
            [_collectionView registerClass:[JLTPhotoCell class] forCellWithReusEIDentifier:@"photoCell"];
            [self.view addSubview:self.collectionView];
            self.collectionView.allowsSelection = true;
    }

- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section
{
    NSLog(@"count %i",_thumbNails.count);
    return _thumbNails.count;
}

- (NSInteger)numberOfSectionsInCollectionView: (UICollectionView *)collectionView
{
    return 1;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemATindexPath:(NSIndexPath *)indexPath
{
    if (_thumbNails.count > 0)
    {
        JLTPhotoCell *cell = [cv dequeueReusableCellWithReusEIDentifier:@"photoCell" forIndexPath:indexPath];

        NSData *thumbnailData = ((LASignature*)[_thumbNails objectATindex:indexPath.row]).signatureImage;
        UIImage* thumbnailImage = [UIImage imageWithData:thumbnailData];
        [cell setThumbnail:thumbnailImage];
        NSLog(@"image:%@",thumbnailImagE);

        if (!_buttonSELEct.hidden)
        {
            [cell performSELEcted:falSE];
        }

        return cell;
    }

    return nil;
}

#pragma mark UICollectionViewDelegate Methods

-(void) collectionView:(UICollectionView *)collectionView didSELEctItemATindexPath:(NSIndexPath *)indexPath
{
    _lastSELEctedSign = [_thumbNails objectATindex:indexPath.row];

    if (!self.buttonSELEct.hidden)
    {
        JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemATindexPath:indexPath];
        cell.SELEcted = falSE;

    }
    else
    {
        [_SELEctedImages addObject:[_thumbNails objectATindex:indexPath.row]];
        JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemATindexPath:indexPath];
        [cell performSELEcted:TRUE];
      //  _buttondelete.enabled = _SELEctedImages.count > 0;
    }

}

-(void) collectionView:(UICollectionView *)collectionView didDeSELEctItemATindexPath:(NSIndexPath *)indexPath
{
    [_SELEctedImages removeObject:[_thumbNails objectATindex:indexPath.row]];

    JLTPhotoCell *cell = (JLTPhotoCell *)[_collectionView cellForItemATindexPath:indexPath];
    [cell performSELEcted:falSE];
    _buttondelete.enabled = _SELEctedImages.count > 0;

}

#pragma mark - UICollectionViewDelegateFlowLayout
-(CGSizE) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemATindexPath:(NSIndexPath *)indexPath
{
   return  CGSizeMake(50,50) ;
}

-(UIEdgeInsets) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewFlowLayout *)collectionViewLayout insetForSectionATindex:(NSInteger)section
{
    collectionViewLayout.minimumInteritemSpacing=1;
    collectionViewLayout.minimumLinespacing =2;
    return UIEdgeInsetsmake(1,1,1);
}

jltPhotoCell Class
-(void) setThumbnail:(UIImage *) thumbnail
{
    [self setThumbnail:thumbnail andWithSize:(CGSizeMake(50,50))];
}

-(void) setThumbnail:(UIImage *) thumbnail andWithSize:(CGSizE) size
{
    UIImageView *thumbImageView = [[UIImageView alloc] initWithImage:thumbnail];
    thumbImageView.frame = CGRectMake(0,size.width,size.height);
    thumbImageView.userInteractionEnabled = YES;
    [self.contentView addSubview:thumbImageView];
}

-(void) performSELEcted:(bool)SELEcted
{
    if (SELEcted)
    {
        UIImageView *deleteImageView = [[UIImageView alloc] initWithImage:[UIImage imagenamed:@"delete"]];
        deleteImageView.frame = CGRectMake(self.contentView.frame.size.width - 35,3,32,32);
        deleteImageView.tag = 123;
        [self.contentView addSubview:deleteImageView];
    }
    else
    {
        UIView *v = [self.contentView viewWithTag:123];
        v.hidden = YES;
        [self.contentView bringSubviewToFront:v];
        [v removeFromSuperview];
    }
}

任何建议将不胜感激.谢谢.

self.collectionView.delegate = self;
self.collectionView.datasource = self;

self.collectionView.datasource = self;
self.collectionView.delegate = self;