在字或边界处截断包含表情符号或unicode字符的字符串

Question

如何在不消除可能在我的长度中间发出的unicode字符的情况下截断给定长度的字符串？如何确定字符串中unicode字符开头的索引,以便我可以避免创建丑陋的字符串.具有A可见的一半的正方形是另一个被截断的表情符号字符的位置.

-(NSMutableAttributedString*)constructStatusAttributedStringWithRange:(CFRange)range

NSString *original = [_postDictionay objectForKey:@"message"];

NSMutableString *truncated = [NSMutableString string];

NSArray *components = [original componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

for(int x=0; x<[components count]; x++)
{
    //If the truncated string is still shorter then the range desired. (leave space for ...)
    if([truncated length]+[[components objectAtIndex:x] length]<range.length-3)
    {
        //Just checking if its the first word
        if([truncated length]==0 && x==0)
        {
            //start off the string
            [truncated appendString:[components objectAtIndex:0]];
        }
        else
        {
            //append a new word to the string
            [truncated appendFormat:@" %@",[components objectAtIndex:x]];
        }

    }
    else
    {
        x=[components count];
    }
}

if([truncated length]==0 || [truncated length]< range.length-20)
{
    truncated = [NSMutableString stringWithString:[original substringWithRange:NSMakeRange(range.location, range.length-3)]];
}

[truncated appendString:@"..."];

NSMutableAttributedString *statusString = [[NSMutableAttributedString alloc]initWithString:truncated];
[statusString addAttribute:(id)kCTFontAttributeName value:[StyleSingleton streamStatusFont] range:NSMakeRange(0, [statusString length])];
[statusString addAttribute:(id)kCTForegroundColorAttributeName value:(id)[StyleSingleton streamStatusColor].CGColor range:NSMakeRange(0, [statusString length])];

return statusString;

}

更新感谢答案,能够根据我的需求使用一个简单的功能!

-(NSMutableAttributedString*)constructStatusAttributedStringWithRange:(CFRange)range
{
NSString *original = [_postDictionay objectForKey:@"message"];

NSMutableString *truncated = [NSMutableString stringWithString:[original substringWithRange:[original rangeOfComposedCharacterSequencesForRange:NSMakeRange(range.location, range.length-3)]]];
[truncated appendString:@"..."];

NSMutableAttributedString *statusString = [[NSMutableAttributedString alloc]initWithString:truncated];
[statusString addAttribute:(id)kCTFontAttributeName value:[StyleSingleton streamStatusFont] range:NSMakeRange(0, [statusString length])];
[statusString addAttribute:(id)kCTForegroundColorAttributeName value:(id)[StyleSingleton streamStatusColor].CGColor range:NSMakeRange(0, [statusString length])];

return statusString;

}

Answer 1

NSString有一个方法rangeOfComposedCharacterSequencesForRange可用于在字符串中查找仅包含完整组合字符的封闭范围.例如

NSString *s =  @"";
NSRange r = [s rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, 1)];

给出范围,{ 0, 2 }因为表情符号字符在字符串中存储为两个UTF-16字符(代理对).

备注:您还可以通过使用来检查是否可以简化第一个循环

enumerateSubstringsInRange:options:usingBlock

有NSStringEnumerationByWords选项.