IOS，NSLayoutConstraint 问题

Question

我有一个自定义 UITableViewCell，我正在尝试自动布局 UILabel，因为它的文本可以有任意长度，但我收到此错误:

Break on objc_exception_throw to catch this in the debugger.
        The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
        2014-09-14 10:20:37.693 InstantForum[29658:60b] 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:0x9aea2e0 V:|-(45)-[UILabel:0x9ae9f30]   (Names: '|':UITableViewCellContentView:0x9ae9250 )>",
            "<NSLayoutConstraint:0x9aea330 V:[UILabel:0x9ae9f30(>=10)]>",
            "<NSLayoutConstraint:0x9aea380 V:[UILabel:0x9ae9f30]-(NSSpace(20))-|   (Names: '|':UITableViewCellContentView:0x9ae9250 )>",
            "<NSAutoresizingMaskLayoutConstraint:0x8c8a750 h=--& v=--& V:[UITableViewCellContentView:0x9ae9250(44)]>"
        )

        Will attempt to recover by breaking constraint 
        <NSLayoutConstraint:0x9aea380 V:[UILabel:0x9ae9f30]-(NSSpace(20))-|   (Names: '|':UITableViewCellContentView:0x9ae9250 )>

        Break on objc_exception_throw to catch this in the debugger.
        The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful

这是我的 UITableViewCell 中的代码，这是我在单元格中设置 subview 的位置:

-(void)setupView:(PostInfo*)postInfo{


            CGRect screenRect = [[UIScreen mainScreen] bounds];
            viewPostMessage = [[UIView alloc] initWithFrame:CGRectMake(10, 10, screenRect.size.width - 20, 100)];
            viewPostMessage.backgroundColor = [UIColor colorWithRed:193.0f/255 green:193.0f/255 blue:193.0f/255 alpha:1.0f];
            viewPostMessage.layer.borderColor = [UIColor blackColor].CGColor;
            viewPostMessage.layer.borderWidth = 0.5f;


            dispatch_queue_t concurrentQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

            // 3) Load picker in background

            userImage = [[UIImageView alloc] initWithFrame:CGRectMake(10, 10, 30, 30)];
            [self.contentView addSubview:userImage];


            if(postInfo.userImage.length > 0){
            __block UIImage *imageUser;

            dispatch_async(concurrentQueue, ^{

                imageUser =  [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString: [NSString stringWithFormat:@"http://www.hugt.co.uk/userimage/%d/userImage.jpg", postInfo.userId]]]];

                dispatch_async(dispatch_get_main_queue(), ^{

                userImage.image = imageUser;

                });

            });


            }else{
            UIView *viewImage = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 30, 30)];
            viewImage.backgroundColor = [UIColor colorWithRed:132.0f/255 green:132.0f/255 blue:132.0f/255 alpha:1.0f];
            [self.contentView addSubview:viewImage];

            userImage = [[UIImageView alloc] initWithFrame:CGRectMake(5, 5, 20, 20)];
            UIImage *imageUser = [UIImage imageNamed:@"defaultuser.jpg"];
            userImage.image = imageUser;
            [viewImage addSubview:userImage];
            }

            labelUserName = [[UILabel alloc] initWithFrame:CGRectMake(50, 8, 200, 16)];
            labelUserName.textColor = [UIColor colorWithRed:56.0f/255 green:56.0f/255 blue:57.0f/255 alpha:1.0f];
            labelUserName.text = [NSString stringWithFormat:@"%@ %@ posted...", postInfo.firstName,postInfo.lastName];
            //labelFirstName.textAlignment = NSTextAlignmentCenter;
            labelUserName.font = [UIFont fontWithName:@"Helvetica" size:12];
            labelUserName.userInteractionEnabled = YES;
            [self.contentView addSubview:labelUserName];

            labelCreated = [[UILabel alloc] initWithFrame:CGRectMake(50, 24, 200, 16)];
            labelCreated.textColor = [UIColor colorWithRed:86.0f/255 green:152.0f/255 blue:179.0f/255 alpha:1.0f];
            labelCreated.text = [NSDateFormatter localizedStringFromDate:postInfo.timeStampCreated dateStyle:NSDateFormatterMediumStyle timeStyle:NSDateFormatterMediumStyle];
            labelCreated.text = [labelCreated.text stringByReplacingOccurrencesOfString:@"AM" withString:@""];
            labelCreated.text = [labelCreated.text stringByReplacingOccurrencesOfString:@"PM" withString:@""];
            //labelFirstName.textAlignment = NSTextAlignmentCenter;
            labelCreated.font = [UIFont fontWithName:@"Helvetica" size:12];
            labelCreated.userInteractionEnabled = YES;
            [self.contentView addSubview:labelCreated];

            labelMessage = [[UILabel alloc] initWithFrame:CGRectMake(50, 43, 210, 9999)];
            labelMessage.textColor = [UIColor colorWithRed:141.0f/255 green:142.0f/255 blue:142.0f/255 alpha:1.0f];
            labelMessage.text = postInfo.message;
            //labelMessage.numberOfLines = 0;
            //labelFirstName.textAlignment = NSTextAlignmentCenter;
            labelMessage.font = [UIFont fontWithName:@"Helvetica" size:12];
            labelMessage.userInteractionEnabled = YES;
            labelMessage.lineBreakMode = NSLineBreakByWordWrapping;
            labelMessage.translatesAutoresizingMaskIntoConstraints = NO;
            [labelMessage sizeToFit];
            [self.contentView addSubview:labelMessage];

            //NSDictionary *views = NSDictionaryOfVariableBindings(labelMessage);
            //labelMessage.translatesAutoresizingMaskIntoConstraints = NO;





            [self.contentView addConstraints:[NSLayoutConstraint
                           constraintsWithVisualFormat:@"V:|-45-[labelMessage(>=10)]-|"
                           options:NSLayoutFormatDirectionLeadingToTrailing
                           metrics:nil
                           views:NSDictionaryOfVariableBindings(userImage,labelUserName,labelCreated,labelMessage)]];

            [self.contentView addConstraints:[NSLayoutConstraint
                           constraintsWithVisualFormat:@"H:|-10-[labelMessage(==210)]-|"
                           options:NSLayoutFormatDirectionLeadingToTrailing
                           metrics:nil
                           views:NSDictionaryOfVariableBindings(userImage,labelUserName,labelCreated,labelMessage)]];
            //self.contentView.translatesAutoresizingMaskIntoConstraints = NO;
            //self.clipsToBounds = YES;
            //[self.contentView addSubview:viewPostMessage];

        }

Answer 1

垂直约束定义为距离 super View 顶部有 45 点的边距，距离 super View 底部的默认边距为 20 点，最小标签高度为 10 点。这意味着 contentView 的最小高度应该是 75 点。要使这些约束正确无误地适应，您必须减少边距或增加 contentView 的大小。

要删除默认边距限制，您可以简单地删除破折号，如下所示。

@"V:|-45-[labelMessage(>=10)]|"

水平约束也可能需要调整。它的约束定义为距离 super View 左侧 10 点，距离 super View 右侧的默认边距，标签的精确宽度为 210 点。您可能希望删除这三个约束之一以防止任何冲突。

这是一个删除尾随约束的示例。

@"H:|-10-[labelMessage(==210)]"