ios添加UICollectionView报错

我添加了UICollectionView到view中。然后报错了。

错误：
`
"NSInvalidArgumentException', reason: '-[NSIndexPath reuseIdentifier]: unrecognized selector sent to instance"
`

方法：

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

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *identifier = @"CellID";
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];

    UIImageView *imageView = (UIImageView *)[cell viewWithTag:10];
    imageView.image = [UIImage imageNamed:@"V.jpg"];
}

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