UICollectionView委托方法cellForItemAtIndexPath：indexPath未从sizeForItemAtIndexPath调用 [英] UICollectionView delegate method cellForItemAtIndexPath:indexPath not called from sizeForItemAtIndexPath

问题描述

当我调用

  [collectionView cellForItemAtIndexPath：indexPath：] 
  pre> 
 
 
从内部
  [collectionView：layout：sizeForItemAtIndexPath：] 
  
那么委托方法不会被触发。任何想法为什么不？
 
 
 
您可以看到 here 。
   - （UICollectionViewCell *）collectionView：（UICollectionView *） collectionView cellForItemAtIndexPath：（NSIndexPath *）indexPath {
 
 CustomCell * cell = [self.collectionView dequeueReusableCellWithReuseIdentifier：@CustomCellforIndexPath：indexPath]; 
 
 [cell configureWithData：self.data [indexPath.row]]; 
 
 return cell; 
} 
 
 
  - （CGSize）collectionView：（UICollectionView *）collectionView布局：（UICollectionViewLayout *）collectionViewLayout sizeForItemAtIndexPath：（NSIndexPath *）indexPath {
 
 CustomCell * cell =（CustomCell *）[collectionView cellForItemAtIndexPath：indexPath]; 
 
 return [cell prefferedSize]; 
} 
  
我想要做的是要求单元格的优先大小。 / p> 
 
 
我可以做
  CustomCell * cell = self collectionView：collectionView cellForItemAtIndexPath：indexPath]; 
  
但触发了一个永无止境的循环。
 
 
 
为什么它的委托方法不会被调用，因为它应该是？
解决方案
实例方法
   - （CGSize）collectionView：（UICollectionView *）collectionView布局：（UICollectionViewLayout *）collectionViewLayout sizeForItemAtIndexPath：（NSIndexPath *） indexPath {
 
 return [CustomCell prefferedSizeWithData：self.data [indexPath.row]; 
 
} 
  
我为单元格创建了Class方法...这个方法我提供在指定的indexPath的实例实例将持有并计算优先的大小的数据
 
 
 
 i 
  CustomCell * cell =（CustomCell *）[collectionView cellForItemAtIndexPath：indexPath]; 
  
触发internaly 
   - （CGSize）collectionView：（UICollectionView *）collectionView布局：（UICollectionViewLayout *）collectionViewLayout sizeForItemAtIndexPath：（NSIndexPath *）indexPath 
  
我们看到的是一些来自苹果的机制，以防止循环...因为直接调用
  CustomCell * cell =（CustomCell *）[self collectionView：collectionView cellForItemAtIndexPath：indexPath]; 
  
会导致循环周期
 
When I call 
[collectionView cellForItemAtIndexPath:indexPath:]
from inside 
[collectionView:layout:sizeForItemAtIndexPath:]
then the delegate method is not triggered. Any idea why not?

You can see it here.
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    CustomCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:@"CustomCell" forIndexPath:indexPath];

    [cell configureWithData:self.data[indexPath.row]];

    return cell;
}


- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    CustomCell * cell = (CustomCell *)[collectionView cellForItemAtIndexPath:indexPath];

    return [cell prefferedSize];
}
What i want to do is to ask the cell for its preffered size.

I could do
CustomCell * cell = (CustomCell *)[self collectionView:collectionView cellForItemAtIndexPath:indexPath];
but then a never ending loop cycle is triggered

why is its delegate method not called as it should be?
解决方案
i ended up with a Class method instead of an instance method
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    return [CustomCell prefferedSizeWithData:self.data[indexPath.row]; 

}
i made a Class method for the cell... to this method i provide the data that an acctual instance at the specified indexPath would hold and calculate the preffered size

i thing that 
CustomCell * cell = (CustomCell *)[collectionView cellForItemAtIndexPath:indexPath];
triggers internaly 
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath 
and what we see is some mechanism from Apple to prevent a loop cycle... because calling directly
CustomCell * cell = (CustomCell *)[self collectionView:collectionView cellForItemAtIndexPath:indexPath];
results in a loop cycle

                        
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