iOS表格视图单元格无法在初始视图上进行渲染

Question

我有一个带自定义单元格的UITableView。细胞内部有各种标签的“uiview”。

在第一次观看桌子时，细胞从未正确计算它们的高度。但是，如果我点击另一个视图并返回单元格高度，就像在预览图像中一样。

我的cellForRowAtIndexPath函数非常标准，如下所示：

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{
let cell = tableView.dequeueReusableCellWithIdentifier("PostCell", forIndexPath: indexPath) as! PostCell
if let frc = fetchedResultsController {
    if let post = frc.objectAtIndexPath(indexPath) as? Post {
        var name = post.user.username
        cell.nameLabel.text = name
        cell.subtitleLabel.text = "\(post.created_at.timeAgoFormat())"
        let imageUrl = NSURL(string: post.user.profile_image_url)
        cell.userImage!.hnk_setImageFromURL( imageUrl! )
        cell.messageLabel.text = "Beta testing is never fun when it doesn't load like you wished it would.."
    }
}
return cell
}

我尝试了各种其他stackoverflow答案但没有成功，例如：

cell.messageLabel.preferredMaxLayoutWidth = cell.messageLabel.frame.size.width
cell.cardView.sizeToFit()
cell.setNeedsLayout()
cell.layoutIfNeeded()
cell.messageLabel.preferredMaxLayoutWidth = CGRectGetWidth(cell.messageLabel.frame)

override func didMoveToSuperview() {
    self.layoutIfNeeded()
}

messageLabel的行设置为0

viewDidLoad有

self.tableView.estimatedRowHeight = 300.0
self.tableView.rowHeight = UITableViewAutomaticDimension

自动布局约束均设置为具有单个顶部，底部，前导和尾随约束的视图，并且在模拟器中查看之前不会显示任何问题。这似乎有点奇怪，虽然我删除了除了和messageLabel和卡片UIView之外的所有视图，并且给了它们所有4个约束到superview仍然给出了错误。

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x7ffe0445b7e0 V:[UIView:0x7ffe01e4a1e0]-(0)-|   (Names: '|':UITableViewCellContentView:0x7ffe01e4a0c0 )>",
    "<NSLayoutConstraint:0x7ffe044652a0 V:|-(10)-[UIView:0x7ffe01e4a1e0]   (Names: '|':UITableViewCellContentView:0x7ffe01e4a0c0 )>",
    "<NSLayoutConstraint:0x7ffe04472770 V:[UILabel:0x7ffe01e4a2f0'Beta testing is never fun...']-(8)-|   (Names: '|':UIView:0x7ffe01e4a1e0 )>",
    "<NSLayoutConstraint:0x7ffe04461fa0 V:[UIView:0x7ffe01d67d40]-(0)-[UILabel:0x7ffe01e4a2f0'Beta testing is never fun...']>",
    "<NSLayoutConstraint:0x7ffe0446fa80 V:|-(0)-[UIView:0x7ffe01d67d40]   (Names: '|':UIView:0x7ffe01e4a1e0 )>",
    "<NSLayoutConstraint:0x7ffe04466cb0 V:[UIView:0x7ffe01d67d40(55)]>",
    "<NSLayoutConstraint:0x7ffe044db690 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x7ffe01e4a0c0(43.5)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7ffe04466cb0 V:[UIView:0x7ffe01d67d40(55)]>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2015-08-14 15:52:22.362 Birdie[14262:8821397] Unable to simultaneously satisfy constraints.

有关进一步参考，请参阅Post Cell

import UIKit
class PostCell: UITableViewCell {
    @IBOutlet weak var cardView: UIView!
    @IBOutlet weak var nameLabel: UILabel!
    @IBOutlet weak var subtitleLabel: UILabel!
    @IBOutlet weak var userImage: UIImageView!
    @IBOutlet weak var messageLabel: UILabel!
    override func awakeFromNib() {
        super.awakeFromNib()
    }
    override func layoutSubviews() {
        self.cardSetup()
    }
    override func setSelected(selected: Bool, animated: Bool) {
        super.setSelected(selected, animated: animated)
    }
    func cardSetup(){
        self.cardView.alpha = 1
        self.cardView.layer.masksToBounds = false
        self.cardView.layer.cornerRadius = 2

        self.cardView.layer.shadowOffset = CGSizeMake(CGFloat(-0.2), CGFloat(0.2))
        self.cardView.layer.shadowRadius = 1
        self.cardView.layer.shadowOpacity = 0.2
        var path = UIBezierPath(rect:  self.cardView.bounds)
        self.cardView.layer.shadowPath = path.CGPath
        self.backgroundColor = UIColor(red: 0.953, green: 0.953, blue: 0.953, alpha: 1)
    }
}

还有其他想法吗？ iOS 8模拟器，xcode 6.4