我在XIB文件中有一个具有动态高度的自定义单元格,该文件显示带有消息和图像的帖子.因为图像将从我的API异步加载,所以图像的宽高比将随资源一起发送.在updateConstraints方法中,将设置具有适当乘数的宽高比约束.
XIB文件：
细胞类：
//
// PostTableViewCell.swift
// Lome
//
// Created by Tobias Feistmantl on 10/09/15.
// Copyright (c) 2015 Tobias Feistmantl. All rights reserved.
//
import UIKit
import Alamofire
class PostTableViewCell: UITableViewCell {
@IBOutlet weak var userProfileImageView: TFImageView!
@IBOutlet weak var usersNameLabel: UILabel!
@IBOutlet weak var usernameLabel: UILabel!
@IBOutlet weak var userProfileButton: TFCellButton!
@IBOutlet weak var distanceLabel: UILabel!
@IBOutlet weak var messageLabel: UILabel!
@IBOutlet weak var postImageView: UIImageView!
@IBOutlet weak var likeCountLabel: UILabel!
@IBOutlet weak var timestampLabel: UILabel!
@IBOutlet weak var likeButton: UIButton!
@IBOutlet weak var constraintBetweenMessageLabelAndPostImageView: NSLayoutConstraint!
var post: Post! {
didSet {
post.author.profileImage(version: .Thumbnail) { image,_ in
self.userProfileImageView.image = image
}
if let name = post.author.fullName {
usersNameLabel.text = name
usernameLabel.text = post.author.username
} else {
usersNameLabel.text = post.author.username
usernameLabel.hidden = true
}
if let attributedMessage = post.attributedMessage {
messageLabel.attributedText = attributedMessage
messageLabel.hidden = false
constraintBetweenMessageLabelAndPostImageView.constant = 15
} else {
messageLabel.hidden = true
messageLabel.attributedText = nil
constraintBetweenMessageLabelAndPostImageView.constant = 0
}
post.image { image,_ in
if let image = image {
self.postImageView.image = image
self.setNeedsUpdateConstraints()
}
}
timestampLabel.text = "Posted \(post.createdAt.timeAgoSinceNow())"
distanceLabel.text = post.distanceText
likeCountLabel.text = "\(post.likesCount) Likes"
likeButton.setImage(post.likeButtonImage,forState: .Normal)
}
}
override func updateConstraints() {
if let aspectRatio = post.imageAspectRatio {
postImageAspectConstraint = NSLayoutConstraint(item: postImageView,attribute: NSLayoutAttribute.Width,relatedBy: NSLayoutRelation.Equal,toItem: postImageView,attribute: NSLayoutAttribute.Height,multiplier: CGFloat(aspectRatio),constant: 0)
}
super.updateConstraints()
}
func setupUserProfileButton(indexPath: NSIndexPath,viewController: UIViewController) {
userProfileButton.indexPath = indexPath
userProfileButton.addTarget(viewController,action: "userProfileButtonDidTouch:",forControlEvents: .TouchUpInside)
}
var postImageAspectConstraint: NSLayoutConstraint? {
didSet {
if let oldValue = oldValue {
postImageView.removeConstraint(oldValue)
}
if let postImageAspectConstraint = postImageAspectConstraint {
postImageView.addConstraint(postImageAspectConstraint)
}
}
}
override func prepareForReuse() {
super.prepareForReuse()
postImageAspectConstraint = nil
}
}
cellForRowAtIndexPath方法：
func tableView(tableView: UITableView,cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("postCell",forIndexPath: indexPath) as! PostTableViewCell
cell.post = posts[indexPath.row]
cell.setupUserProfileButton(indexPath,viewController: self)
return cell
}
在应用程序启动时,一切都按预期工作,但如果我稍微晃动,约束开始破坏,图像的方面不再正确或其他一些奇怪的事情如下：
错误：
2015-09-28 11:58:27.546 Lome[32812:528936] 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:0x7f8a008bf6f0 V:[Lome.TFImageView:0x7f8a008bf470(35)]>","<NSLayoutConstraint:0x7f89f9fbc490 V:|-(15)-[Lome.TFCellButton:0x7f8a0087fde0] (Names: '|':UITableViewCellContentView:0x7f8a008bf270 )>","<NSLayoutConstraint:0x7f8a00831520 Lome.TFCellButton:0x7f8a0087fde0.top == Lome.TFImageView:0x7f8a008bf470.top>","<NSLayoutConstraint:0x7f8a008315c0 Lome.TFCellButton:0x7f8a0087fde0.bottom == Lome.TFImageView:0x7f8a008bf470.bottom>","<NSLayoutConstraint:0x7f8a00831750 V:[Lome.TFCellButton:0x7f8a0087fde0]-(18)-[UILabel:0x7f8a008806d0'Water']>","<NSLayoutConstraint:0x7f8a00831840 H:|-(0)-[UIImageView:0x7f8a00830910] (Names: '|':UITableViewCellContentView:0x7f8a008bf270 )>","<NSLayoutConstraint:0x7f8a00831890 H:[UIImageView:0x7f8a00830910]-(0)-| (Names: '|':UITableViewCellContentView:0x7f8a008bf270 )>","<NSLayoutConstraint:0x7f8a008318e0 V:[UILabel:0x7f8a008806d0'Water']-(15)-[UIImageView:0x7f8a00830910]>","<NSLayoutConstraint:0x7f8a00831930 V:[UIImageView:0x7f8a00830910]-(20)-[UILabel:0x7f8a00830b90'0 Likes']>","<NSLayoutConstraint:0x7f8a00831980 V:[UILabel:0x7f8a00830b90'0 Likes']-(20)-| (Names: '|':UITableViewCellContentView:0x7f8a008bf270 )>","<NSLayoutConstraint:0x7f8a00860870 UIImageView:0x7f8a00830910.width == 0.6672*UIImageView:0x7f8a00830910.height>","<NSLayoutConstraint:0x7f8a0084e990 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x7f8a008bf270(611)]>","<NSLayoutConstraint:0x7f8a0084f930 'UIView-Encapsulated-Layout-Width' H:[UITableViewCellContentView:0x7f8a008bf270(375)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7f8a008bf6f0 V:[Lome.TFImageView:0x7f8a008bf470(35)]>
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.
2015-09-28 11:58:27.547 Lome[32812:528936] 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:0x7f89f9fbc490 V:|-(15)-[Lome.TFCellButton:0x7f8a0087fde0] (Names: '|':UITableViewCellContentView:0x7f8a008bf270 )>","<NSLayoutConstraint:0x7f8a0084f930 'UIView-Encapsulated-Layout-Width' H:[UITableViewCellContentView:0x7f8a008bf270(375)]>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7f8a00860870 UIImageView:0x7f8a00830910.width == 0.6672*UIImageView:0x7f8a00830910.height>
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.
我认为它与重用单元格有关,但正如您所看到的那样,约束将在prepareForReuse方法中被删除.
我目前非常沮丧,因为我试图解决这个问题几天,但没有找到解决方案.
我希望有人有解决方案.
提前致谢.
解决方法
此问题是由应用于ImageView的2个冲突约束引起的.如果你看一下调试器输出
Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7f8a00860870 UIImageView:0x7f8a00830910.width == 0.6672*UIImageView:0x7f8a00830910.height>
您已经将ImageView的水平约束固定到超级视图,间距为0.
现在,在更新宽高比约束时,您尝试将ImageView的宽度(通过保持宽度作为第一项)设置为其高度的比率,这将导致与其的前导/尾随约束冲突.
您需要通过交换第一个和第二个项目并反转宽高比因子来设置此ImageView的高度.
postImageAspectConstraint = NSLayoutConstraint(item: postImageView,multiplier: 1/CGFloat(aspectRatio),constant: 0)
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