How to set UILabel only width and height and constraints programmatically

问题

I want to create a UILabel programmatically with height, width and then I want to add constraints to it also programmatically for positioning the UILabel.

Update:

I want to create UI like this:

How to create this UI All programatically

Code to create one label label1 similarly I created two more label label2 and label3

UILabel *label1 = [[UILabel alloc]init];

label1.font = TitleFont;
label1.numberOfLines=0;
label1.text= @"Descriptions";
label1.lineBreakMode=NSLineBreakByWordWrapping;
[label1 sizeToFit];
label1.backgroundColor=[UIColor blueColor];
label1.textColor=[UIColor blackColor];
label1.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:label1];

And now I am able to add horizontal constraints them with this code

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[label1]-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(label1)]];

I am also able to set vertical constraint with view but I am unable to set constraint with from one label to another.

回答1:

To create label with height and width constraints here is the constraints...And don't forget to add label in to view with addSubview method

UILabel *Label = [[UILabel alloc] init];
[Label setTranslatesAutoresizingMaskIntoConstraints:NO];  

[self.view addSubview:Label];

// Width constraint
[Label addConstraint:[NSLayoutConstraint constraintWithItem:Label
                                                      attribute:NSLayoutAttributeWidth
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:nil
                                                      attribute: NSLayoutAttributeNotAnAttribute
                                                     multiplier:1
                                                       constant:200]];

// Height constraint
[Label addConstraint:[NSLayoutConstraint constraintWithItem:Label
                                                      attribute:NSLayoutAttributeHeight
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:nil
                                                      attribute: NSLayoutAttributeNotAnAttribute
                                                     multiplier:1
                                                       constant:21]];

Swift 4:

label.translatesAutoresizingMaskIntoConstraints = false
label.addConstraint(NSLayoutConstraint(item: label, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 21))
label.addConstraint(NSLayoutConstraint(item: label, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200))

And In Swift

 Label.setTranslatesAutoresizingMaskIntoConstraints(false)
 self.view.addSubview(Label)

 Label.addConstraint(NSLayoutConstraint(item: Label, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 21))
 Label.addConstraint(NSLayoutConstraint(item: Label, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 200))  

Check this link for more detail

UPDATE
As you update your question, here is my updated answer...

UILabel *Label1 = [[UILabel alloc] init];
[Label1 setTranslatesAutoresizingMaskIntoConstraints:NO];
UILabel *Label2 = [[UILabel alloc] init];
[Label2 setTranslatesAutoresizingMaskIntoConstraints:NO];

Label1.text = @"Label1";
Label1.backgroundColor = [UIColor blueColor];
Label2.text = @"Label2";
Label2.backgroundColor = [UIColor redColor];

[self.view addSubview:Label1];
[self.view addSubview:Label2];

// Width constraint
[Label1 addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                  attribute:NSLayoutAttributeWidth
                                                  relatedBy:NSLayoutRelationEqual
                                                     toItem:nil
                                                  attribute: NSLayoutAttributeNotAnAttribute
                                                 multiplier:1
                                                   constant:280]];

// Height constraint
[Label1 addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                  attribute:NSLayoutAttributeHeight
                                                  relatedBy:NSLayoutRelationEqual
                                                     toItem:nil
                                                  attribute: NSLayoutAttributeNotAnAttribute
                                                 multiplier:1
                                                   constant:21]];

// CenterX constraint
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view
                                                   attribute:NSLayoutAttributeCenterX
                                                   relatedBy:NSLayoutRelationEqual
                                                      toItem:Label1
                                                   attribute: NSLayoutAttributeCenterX
                                                  multiplier:1
                                                    constant:0]];
// Top constraint
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                      attribute:NSLayoutAttributeTop
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:self.topLayoutGuide
                                                      attribute: NSLayoutAttributeBottom
                                                     multiplier:1
                                                       constant:40]];


// label2
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                      attribute:NSLayoutAttributeLeading
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:Label2
                                                      attribute: NSLayoutAttributeLeading
                                                     multiplier:1
                                                       constant:0]];
// label2.Height = label1.Height
[self.view  addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                      attribute:NSLayoutAttributeHeight
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:Label2
                                                      attribute: NSLayoutAttributeHeight
                                                     multiplier:1
                                                       constant:0]];
// label2.width = label1.width
[self.view  addConstraint:[NSLayoutConstraint constraintWithItem:Label1
                                                   attribute:NSLayoutAttributeWidth
                                                   relatedBy:NSLayoutRelationEqual
                                                      toItem:Label2
                                                   attribute: NSLayoutAttributeWidth
                                                  multiplier:1
                                                    constant:0]];

// label2.Top
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:Label2
                                                      attribute:NSLayoutAttributeTop
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:Label1
                                                      attribute: NSLayoutAttributeBottom
                                                     multiplier:1
                                                       constant:34]];  

Result Screen

回答2:

i try this method to change height as text length in your label.

put viewdidload

[yourlabel setNumberOfLines:0];
    CGRect mainframe = _lbl_board.frame;
    mainframe.size.height =  [self getLabelHeight:yourlabel];
    yourlabel.frame = mainframe;

method

- (CGFloat)getLabelHeight:(UILabel*)label
{
    CGSize constraint = CGSizeMake(label.frame.size.width, CGFLOAT_MAX);
    CGSize size;

    NSStringDrawingContext *context = [[NSStringDrawingContext alloc] init];
    CGSize boundingBox = [label.text boundingRectWithSize:constraint
                                                  options:NSStringDrawingUsesLineFragmentOrigin
                                               attributes:@{NSFontAttributeName:label.font}
                                                  context:context].size;

    size = CGSizeMake(ceil(boundingBox.width), ceil(boundingBox.height));

    return size.height;
}

回答3:

In Swift 3 : (just replace .Height by .height and .Equal by .equal)

self.addConstraint(NSLayoutConstraint(item: self, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 35))

来源：https://stackoverflow.com/questions/31428795/how-to-set-uilabel-only-width-and-height-and-constraints-programmatically