如何調整UICollectionView單元的大小以適應其內容？

Question

我正在考慮在sizeForItemAt這樣做，但我無法訪問我的單元格內容的高度。試過在cellForItemAt中這樣做，因爲我們在那裏創建單元格的實例，並且可以引用它的所有內容和高度，但在此方法內設置單元格的框架大小似乎不起作用。似乎只能在sizeForItemAt中正確設置尺寸。下面是我試圖做到這一點在cellForItemAt一個例子（注意，在這個方法我想補充這取決於它是否有一個分配的字符串其.text的likesCommentsLabel觀點，這是什麼使高度動態）：

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 
    let feedCell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! FeedCell 

    feedCell.post = posts[indexPath.item] //This executes post setter and didSet in FeedCell class 

    //Determine whether to add likesCommentsLabel 
    if (feedCell.likesCommentsLabel.text != nil) { 
     feedCell.addSubview(feedCell.likesCommentsLabel) 
     feedCell.addConstraintsWithFormat(format: "H:|-12-[v0]|", views: feedCell.likesCommentsLabel) 
     feedCell.addConstraintsWithFormat(format: "V:|-8-[v0(44)]-4-[v1]-4-[v2(200)]-8-[v3(24)]-8-[v4(0.4)][v5(44)]|", views: feedCell.profileImageView, feedCell.statusTextView, feedCell.statusImageView, feedCell.likesCommentsLabel, feedCell.dividerLineView, feedCell.credibilityButton) 

     print("THIS RUNS") 
    } 
    else { 
     feedCell.addConstraintsWithFormat(format: "V:|-8-[v0(44)]-4-[v1]-4-[v2(200)]-8-[v3(0.4)][v4(44)]|", views: feedCell.profileImageView, feedCell.statusTextView, feedCell.statusImageView, feedCell.dividerLineView, feedCell.credibilityButton) 
     print("THIS RUNS MORE") 
    } 

    //Determine size of cell based on status text length 
    if let statusText = posts[indexPath.item].statusText { 
     let rect = NSString(string: statusText).boundingRect(with: CGSize(width: view.frame.width, height: 500), options: NSStringDrawingOptions.usesFontLeading.union(NSStringDrawingOptions.usesLineFragmentOrigin), attributes: [NSFontAttributeName: UIFont.systemFont(ofSize: 14)], context: nil) 

     var knownHeight: CGFloat = 8.0 + 44.0 + 4.0 + 4.0 + 200.0 + 8.0 + 44.0 

     //Add to height of cell, if there's a likes/comments label 
     if (feedCell.likesCommentsLabel.text != nil) { 
      knownHeight = CGFloat(8.0 + 44.0 + 4.0 + 4.0 + 200.0 + 8.0 + 24.0 + 8.0 + 44.0) 
     } 
     else { 
      knownHeight = CGFloat(8.0 + 44.0 + 4.0 + 4.0 + 200.0 + 8.0 + 44.0) 
     } 
     //Calculate y position based off of previous cell. If no previous cell, y = 0. 
     if indexPath.item > 0 { 
      feedCell.frame = CGRect(x: 0, y: ((collectionView.cellForItem(at: collectionView.indexPathsForVisibleItems[indexPath.item - 1])?.frame.origin.y)! + (collectionView.cellForItem(at: collectionView.indexPathsForVisibleItems[indexPath.item - 1])?.frame.height)!), width: view.frame.width, height: rect.height + knownHeight + 20) 
     } 
     else { 
      feedCell.frame = CGRect(x: 0, y: 0, width: view.frame.width, height: rect.height + knownHeight + 20) 
     } 
     print(feedCell.frame) 
    } 

    return feedCell 
} 

Answer 1

覆蓋「viewDidLayoutSubviews」的方法，併爲您的CollectionView像佈局無效，

- (void)viewDidLayoutSubviews { 
    [super viewDidLayoutSubviews]; 
    [yourCollectionView.collectionViewLayout invalidateLayout]; 
} 

然後「sizeForItemAtIndexPath」將工作！