具有异步加载图像的表视图单元格的动态高度
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，那么约束开始破坏，图像的方面不再正确或者其他一些奇怪的东西如下：
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: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: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.
我认为它与重复使用单元格有关，但正如您所见，约束将在prepareForReuse方法中删除。
我目前非常沮丧，因为我试图解决这个问题，因为几天没有找到解决方案。
我希望有人有解决方案。
提前致谢。
3 个答案:
答案 0 :(得分：1)
此问题是由应用于ImageView的2个冲突约束引起的。如果查看调试器输出
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7f8a00860870 UIImageView:0x7f8a00830910.width == 0.6672*UIImageView:0x7f8a00830910.height>
您已经对ImageView的水平约束固定到superview，间距为0。
现在，在更新宽高比限制时，您尝试将width（通过保持宽度作为第一项）设置为ImageView的比例height，这将导致postImageAspectConstraint = NSLayoutConstraint(item: postImageView, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: postImageView, attribute: NSLayoutAttribute.Width, multiplier: 1/CGFloat(aspectRatio), constant: 0)
与它的领先/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。
INTERVAL cast(ActiveDays as text) || ' day'
答案 1 :(得分：0)
一旦获得图像高度，就应该 更新你的数组，例如rowHeightArray，用于跟踪所有rowHeights，例如
[rowHeightArray replaceObjectAtIndex:indexPath.row withObject:[NSNumber numberWithFloat:imageHeight]];
然后致电
[aTableView reloadRowsAtIndexPaths:indexPath withRowAnimation:YES];
它将调用
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
return [[rowHeightArray objectAtIndex:indexPath.row] floatValue];
}
使用行高返回indexPath处的对象。
答案 2 :(得分：0)
要删除约束，请检查：
[aView setTranslatesAutoresizingMaskIntoConstraints:NO];
[aView removeConstraints:view.constraints];
或
for(NSLayoutConstraint *constraint in aView.constraints){
[aView.view removeConstraint:constraint];
}
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