ios - 减少多行 UILabel 中最后一行的宽度

Question

我正在实现一个“阅读更多”功能，很像 Apple 的 AppStore 中的功能。但是，我使用的是多行 UILabel。查看 Apple 的 AppStore，他们如何减小最后可见行的宽度以适应“更多”文本并仍然截断尾部(见图)？

Answer 1

这似乎可行，至少在我进行的有限测试中是这样。有两种公共(public)方法。如果您有多个标签都具有相同行数，则可以使用较短的标签——只需更改顶部的 kNumberOfLines 以匹配您想要的内容。如果您需要传递不同标签的行数，请使用更长的方法。请务必将您在 IB 中制作的标签的类别更改为 RDLabel。使用这些方法代替 setText:。如有必要，这些方法将标签的高度扩展到 kNumberOfLines，如果仍然被截断，将扩展它以适应触摸时的整个字符串。目前，您可以触摸标签中的任何位置。改变它应该不会太难，所以只有靠近 ...Mer 才会导致膨胀。

#import "RDLabel.h"
#define kNumberOfLines 2
#define ellipsis @"...Mer ▾ "

@implementation RDLabel {
    NSString *string;
}

#pragma Public Methods

- (void)setTruncatingText:(NSString *) txt {
    [self setTruncatingText:txt forNumberOfLines:kNumberOfLines];
}

- (void)setTruncatingText:(NSString *) txt forNumberOfLines:(int) lines{
    string = txt;
    self.numberOfLines = 0;
    NSMutableString *truncatedString = [txt mutableCopy];
    if ([self numberOfLinesNeeded:truncatedString] > lines) {
        [truncatedString appendString:ellipsis];
        NSRange range = NSMakeRange(truncatedString.length - (ellipsis.length + 1), 1);
        while ([self numberOfLinesNeeded:truncatedString] > lines) {
            [truncatedString deleteCharactersInRange:range];
            range.location--;
        }
        [truncatedString deleteCharactersInRange:range];  //need to delete one more to make it fit
        CGRect labelFrame = self.frame;
        labelFrame.size.height = [@"A" sizeWithFont:self.font].height * lines;
        self.frame = labelFrame;
        self.text = truncatedString;
        self.userInteractionEnabled = YES;
        UITapGestureRecognizer *tapper = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(expand:)];
        [self addGestureRecognizer:tapper];
    }else{
        CGRect labelFrame = self.frame;
        labelFrame.size.height = [@"A" sizeWithFont:self.font].height * lines;
        self.frame = labelFrame;
        self.text = txt;
    }
}

#pragma Private Methods

-(int)numberOfLinesNeeded:(NSString *) s {
    float oneLineHeight = [@"A" sizeWithFont:self.font].height;
    float totalHeight = [s sizeWithFont:self.font constrainedToSize:CGSizeMake(self.bounds.size.width, CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping].height;
    return nearbyint(totalHeight/oneLineHeight);
}

-(void)expand:(UITapGestureRecognizer *) tapper {
    int linesNeeded = [self numberOfLinesNeeded:string];
    CGRect labelFrame = self.frame;
    labelFrame.size.height = [@"A" sizeWithFont:self.font].height * linesNeeded;
    self.frame = labelFrame;
    self.text = string;
}