determine the maximum number of characters a UILabel can take

问题

Given a UILabel and a NSString, how do I determine how much of the string can fit inside the UILabel? I am using Xcode-5 and iOS-7.

I have been trying to see what I can extract from the thread Calculating UILabel Text Size but I am not getting anywhere with the responses there.

回答1:

Well, what I did here works though there may be another, more efficient (yet less straight-forward) way.

What I did was just calculate the size of the rect needed for the text, see if it fits in the label's frame, and if not, chop off a character and try again.

@interface LTViewController ()

@property (nonatomic, weak) IBOutlet UILabel *label1;
@property (nonatomic, weak) IBOutlet UILabel *label2;

@end

@implementation LTViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    UILabel *label1 = self.label1;
    UILabel *label2 = self.label2;

    UIFont *font = label1.font;
    NSString *text = @"This is some text that will go into labels 1 and 2.";

    CGRect label1Frame = label1.frame;

    NSUInteger numberOfCharsInLabel1 = NSNotFound;

    for (int i = [text length]; i >= 0; i--) {
        NSString *substring = [text substringToIndex:i];
        NSAttributedString *attributedText = [[NSAttributedString alloc] initWithString:substring
                                                                             attributes:@{ NSFontAttributeName : font }];
        CGSize size = CGSizeMake(label1Frame.size.width, CGFLOAT_MAX);
        CGRect textFrame = [attributedText boundingRectWithSize:size
                                                        options:NSStringDrawingUsesLineFragmentOrigin
                                                        context:nil];

        if (CGRectGetHeight(textFrame) <= CGRectGetHeight(label1Frame)) {
            numberOfCharsInLabel1 = i;
            break;
        }
    }

    if (numberOfCharsInLabel1 == NSNotFound) {
        // TODO: Handle this case.
    }

    label1.text = [text substringToIndex:numberOfCharsInLabel1];
    label2.text = [text substringWithRange:NSMakeRange(numberOfCharsInLabel1, [text length] - numberOfCharsInLabel1)];
}

@end

This yields:

It's up to you to handle the error conditions. For example, the rest doesn't completely fit into label2 and it's probably going to chop in the middle of a word more often then not.

回答2:

Here is a swift solution for it:

func visibleSubString(label: UILabel) -> String? {

    let labelFrame = label.frame

    var numberOfCharsInLabel1 = 0

    guard let text = self.text, let fullAttributedText = self.attributedText else { return "" }
    var i = text.count

    while i >= 0 {
        let attributedText: NSAttributedString? = fullAttributedText.attributedSubstring(from: NSRange(location: 0, length: i))
        let size = CGSize(width: labelFrame.size.width , height: CGFloat.greatestFiniteMagnitude)
        if let textFrame = attributedText?.boundingRect(with: size, options: .usesLineFragmentOrigin, context: nil) {
            if textFrame.height <= labelFrame.height {
                numberOfCharsInLabel1 = i
                break
            }
            i -= 1
        }
    }

    let visibleText = (text as NSString).substring(to: numberOfCharsInLabel1)
    return visibleText
}

来源：https://stackoverflow.com/questions/25193520/determine-the-maximum-number-of-characters-a-uilabel-can-take

标签

ios

objective-c

nsstring

uilabel