集合视图中的气泡没有增长到适当的高度

Question

我正在构建一个Chatting View Controller。我的聊天气泡的约束如下：

bubbleViewRightAnchor = bubbleView.rightAnchor.constraintEqualToAnchor(self.rightAnchor, constant: -8)
bubbleView.topAnchor.constraintEqualToAnchor(self.topAnchor).active = true
bubbleWidthAnchor = bubbleView.widthAnchor.constraintEqualToConstant(200)
bubbleWidthAnchor?.active = true
bubbleViewRightAnchor?.active = true
bubbleView.heightAnchor.constraintEqualToAnchor(self.heightAnchor).active = true

bubbleView 内部是一个textView，它被限制在bubbleView 内部，如下所示：

textView.leftAnchor.constraintEqualToAnchor(bubbleView.leftAnchor, constant: 8).active = true
textView.topAnchor.constraintEqualToAnchor(self.topAnchor).active = true
textView.rightAnchor.constraintEqualToAnchor(bubbleView.rightAnchor).active = true
textView.heightAnchor.constraintEqualToAnchor(self.heightAnchor).active = true

所有约束都正常工作，您可以看到聊天气泡的高度锚点被限制为“自我的高度锚点”，自我是collection View cell。因此，无论细胞有什么高度，气泡也会有。气泡内部是一个textView，其中包含用户发送的所有文本。在另一个View Controller中，以下代码根据textview中的文本数量修改collection view cell的高度和宽度如下：

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {

    var height: CGFloat = 80

    if let text = messages[indexPath.item].text {
        height = estimateFrameForText(text).height + 20
    }
    let width = UIScreen.mainScreen().bounds.width

    return CGSize(width: width, height: height)
}

private func estimateFrameForText(text: String) -> CGRect {
    let size = CGSize(width: 200, height: 1000)
    let options = NSStringDrawingOptions.UsesFontLeading.union(.UsesLineFragmentOrigin)
    return NSString(string: text).boundingRectWithSize(size, options: options, attributes: [NSFontAttributeName: UIFont.systemFontOfSize(16)], context: nil)
}

函数estimateframefortext根据文本估计单元格的框架（不知何故，不知道它是如何做到的）。它适用于 600 个字符左右以下的消息，但是，如果您写入更多字符，它会为单元格增加额外 20-30 的高度，被限制到单元格的 bubbleView 也将采用高度，您现在可以见文字下方的空白处。我想知道是否有更精确的函数可以根据文本的多少来估计单元格的高度。

Answer 1

如果你使用的是UITextView，那么你可以使用这个方法：

import UIKit
import XCPlayground

let view = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 500))
view.backgroundColor = UIColor.whiteColor()
XCPlaygroundPage.currentPage.liveView = view

let text = "The function estimateframefortext estimates the frame of the cell based on the text (somehow, no idea how it does it). It works fine for messages under 600 characters or so, however, if you write more characters it adds an extra 20-30 of height to the cell, the bubbleView being constrained to the cell will also adopt the height, where you can now see clear space under the text. I was wondering if there were more precise functions to estimate what the height of a cell should be. \n!!!!!The function estimateframefortext estimates the frame oheightTextThe function estimateframefortext estimates the frame of the cell based on the text (somehow, no idea how it does it). It works fine for messages under 600 characters or so, however, if you write more characters it adds an extra 20-30 of height to the cell, the bubbleView being constrained to the cell will also adopt the height, where you can now see clear space under the text. I was wondering if there were more precise functions to estimate what the height of a cell should be "

let label = UITextView()
view.addSubview(label)
label.text = text

let size = label.sizeThatFits(CGSize(width: view.bounds.width, height: 0))
let heightText = size.height
debugPrint(label.contentSize)
label.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: heightText)
label.layer.borderWidth = 1
label.layer.borderColor = UIColor.redColor().CGColor

或：

let label = UITextView(frame: CGRect(x: 0, y: 0, width: view.bounds.width, height: 0))
view.addSubview(label)
label.text = text
debugPrint(label.contentSize)
label.frame.size = label.contentSize
label.layer.borderWidth = 1
label.layer.borderColor = UIColor.redColor().CGColor

解释：

UITextView 实现了可滚动的行为，当您放置内容[在本例中为文本] 时，textView 符合协议UIScrollView，为此，您可以使用 contentSize 返回内容视图的大小。