如何通过编程调整UILabel上的宽度和高度?

你可以这样做 boundingRectWithSize ...

将标签添加到视图中,并给它一个起始宽度约束(实际上不在乎什么值,因为它将被更改)。

保留对宽度约束的引用(如果使用IB,IBOutlet可以正常工作)。

不要给它高度限制。

设置标签文本时,可以使用此选项更改其宽度:

// get the font of the label
UIFont *theFont = _theLabel.font;

// get the text of the label
NSString *theString = _theLabel.text;

// calculate the bounding rect, limiting the width to the width of the view
CGRect r = [theString boundingRectWithSize:CGSizeMake(self.view.frame.size.width, CGFLOAT_MAX)
                                   options:(NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading)
                                attributes:@{NSFontAttributeName: theFont}
                                   context:nil];

// change the constant of the constraint to the calculated width
_theWidthConstraint.constant = ceil(r.size.width);

// NOTE: If you are *not* using auto-layout, 
// this same calculation can be used to explicitly set
// the .frame of the label.

编辑:

根据OP的要求,可以在这里找到一个完整的、可运行的示例(仅使用代码,没有脚本/IB): https://github.com/DonMag/MultilineLabelFitWidth

编辑2:

GitHub项目已更新。。。现在包括两个手动帧设置的示例 和 自动布局/约束。

通过更多的实验,我发现了一些我还没见过的伎俩。一般来说,它是这样工作的:

• 查找最长的文本行
• 将numberOfLines设置为1(临时)
• 将标签文本设置为最长文本行
• Call label.sizeToFit(设置最长行的标签宽度)
• 将numberOfLines设置为0(多行)
• 将标签文本设置为完整的多行文本
• Call label.sizeToFit(设置所有行的标签高度)

喂!现在,您的UILabel的大小适合您的多行文本。

下面是一个示例(GitHub上的演示项目: UILabelSizeToFitDemo ):

- (UILabel *)label = nil;

- (void)updateLabel:(NSString *)notes {
    // close to the "sticky" notes color
    UIColor *bananaColor = [ViewController colorWithHexString:@"#FFFC79"];

    if (_label == nil) {
        _label = [[UILabel alloc] init];
        _label.numberOfLines = 0;
        _label.textColor = UIColor.blackColor;
        [_label setBackgroundColor:[bananaColor colorWithAlphaComponent:0.9f]];
        _label.textAlignment = NSTextAlignmentLeft;

        [self.view addSubview:_label];
    }

    // make font size based on screen size
    CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat screenHeight = [UIScreen mainScreen].bounds.size.height;
    CGFloat fontSize = MIN(screenWidth,screenHeight) / 12;
    [_label setFont:[UIFont systemFontOfSize:fontSize]];

    // split lines
    NSArray *lines = [notes componentsSeparatedByString:@"\n"];
    NSString *longestLine = lines[0];   // prime it with 1st line

    // fill a temp UILabel with each line to find the longest line
    for (int i = 0; i < lines.count; i++) {
        NSString *line = (NSString *)lines[i];

        if (longestLine == nil || line.length > longestLine.length) {
            longestLine = line;
        }
    }

    // force UILabel to fit the largest line
    [_label setNumberOfLines:1];
    [_label setText:longestLine];
    [_label sizeToFit];

    // make sure it doesn't go off the screen
    if (_label.frame.size.width > screenWidth) {
        CGRect frame = _label.frame;
        frame.size.width = screenWidth - 20;
        _label.frame = frame;
    }
    // now fill with the actual notes (this saves the previous width)
    [_label setNumberOfLines:0];
    [_label setText:notes];
    [_label sizeToFit];


    // center the label in my view
    CGPoint center = CGPointMake(self.view.bounds.size.width / 2, self.view.bounds.size.height / 2);
    [_label setCenter:center];
}

更新: 下面是另一个完整的解决方案,使用 boundinRectWithSize 从@DonMag的代码片段中:

-(void)updateLabel:(NSString *)notes {
    // close to the "sticky" notes color
    UIColor *bananaColor = [ViewController colorWithHexString:@"#FFFC79"];

    if (_label == nil) {
        _label = [[UILabel alloc] init];
        _label.numberOfLines = 0;
        _label.textColor = UIColor.blackColor;
        _label.backgroundColor = [bananaColor colorWithAlphaComponent:0.9f];
        _label.textAlignment = NSTextAlignmentLeft;

        [self.view addSubview:_label];
    }

    // set new text
    _label.text = notes;

    // make font size based on screen size
    CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat screenHeight = [UIScreen mainScreen].bounds.size.height;
    CGFloat fontSize = MIN(screenWidth,screenHeight) / 12;
    [_label setFont:[UIFont systemFontOfSize:fontSize]];

    // calculate the bounding rect, limiting the width to the width of the view
    CGRect frame = [notes boundingRectWithSize:CGSizeMake(self.view.frame.size.width, CGFLOAT_MAX)
                                       options:(NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading)
                                    attributes:@{NSFontAttributeName: _label.font}
                                       context:nil];

    // set frame and then use sizeToFit
    [_label setFrame:frame];
    [_label sizeToFit];

    // center the label in my view
    CGPoint center = CGPointMake(self.view.frame.size.width / 2, self.view.frame.size.height / 2);
    [_label setCenter:center];
}