如何根据图形宽度截断NSString?

一种选择是通过循环尝试不同的尺寸,直到获得正确的宽度。也就是说,从完整字符串开始,如果该字符串比您需要的宽,则用省略号字符替换最后两个字符。循环直到足够窄。

如果您认为您将使用长字符串,您可以向截断点进行二进制搜索,以使其更快一些。

- (NSString*)stringByTruncatingStringWithFont:(UIFont *)font forWidth:(CGFloat)width lineBreakMode:(UILineBreakMode)lineBreakMode {
    NSMutableString *resultString = [[self mutableCopy] autorelease];
    NSRange range = {resultString.length-1, 1};

    while ([resultString boundingRectWithSize:CGSizeMake(FLT_MAX, FLT_MAX) options:NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:attributes context:nil].size.width > width) {
        // delete the last character
        [resultString deleteCharactersInRange:range];
        range.location--;
        // replace the last but one character with an ellipsis
        [resultString replaceCharactersInRange:range withString:truncateReplacementString];
    }
    return resultString;
}

请注意,由于iOS 6,在后台线程上运行此方法不再安全。