iOS 按字節數截取及(普通length截取)字符串-NSString

顯示的效果是：咱們是一個快樂的...(超過必定(例子是8個)數量時，後面的用...代替)

1.第一種狀況字符串的截取。

//1.字符串設置長度，長度限制----字符串（目的：超過length時，後面顯示...代碼以下）
+ (NSString *)stringWithHtml:(NSString *)str length:(CGFloat)length{
    if (!str) return nil;
    if (str  && [str isKindOfClass:[NSString class]]) {
        CGFloat  character = 0;
        const char *chars = [str cStringUsingEncoding:NSUTF8StringEncoding];
        NSUInteger charLength = length;
        if (strlen(chars) <= charLength*3 +1) {//1個漢字或中文字符3個字節，1個英文1個字節（NSUTF8StringEncoding只適用於這個方法）
            return str;
        }
//若是有寬度限制的話，建議用 if(str.length<=length){return str}; 
//缺點是字母或數字或中文與數字字母混合時計算有誤，還會執行下面方法，但比較保險
        //獲取字數(字節數乘以2便可)
        for(int i=0; i< [str length];i++){
            int a = [str characterAtIndex:i];
            if( a >= 0x4e00 && a <= 0x9fa5){ //判斷是否爲中文
                character +=1;
            }else{
                if ((isalpha(a))||(isalnum(a))||isascii(a)) {
                    character+=0.5;
                }else{
                    character +=1;
                }
            }
            if (character > length) {//按字數截取
                if (character == length) {
                      str = [str substringToIndex:i+1];
                }else{
                     str = [str substringToIndex:i];
                }
                str = [str stringByAppendingString:@"..."];
                break;
            }
        }
    }
    return str;
}

2.第二種狀況簡單富文本的截取。

//2.NSAttributedString 按照字符數(中文1個字佔1位)量截取
+ (NSAttributedString*)subString:(NSAttributedString*)str len:(NSInteger)len{
    if (!str) return nil;
    if (str.length <=len) return str;
    NSUInteger count = 0;
    NSMutableAttributedString *sb = [[NSMutableAttributedString alloc]init];
    for (int i = 0; i< str.length; i++) {
        NSRange range = NSMakeRange(i, 1) ;
        NSAttributedString *aStr = [str attributedSubstringFromRange:range];
        count += [aStr.string lengthOfBytesUsingEncoding:NSUTF8StringEncoding]>1?2:1;
        [sb appendAttributedString:aStr];
        if(count >= len*2) {//由於上面已經返回1或2了因此這裏乘以2
            if (i == str.length -1) {
                return sb;
            }else{
                if (sb) {
                    NSMutableAttributedString *temp1 = [[NSMutableAttributedString alloc]initWithAttributedString:sb];
                    [temp1 appendAttributedString:[[NSAttributedString alloc] initWithString:@"..."]];
                    return temp1;
                }
            }
        }
    }
    return str;
}

3.第三種狀況無論是富文本仍是字符串規定用length來判斷長度並截取。

NSString *subTitle = @"服務器返回的富文本或字符串"
    if (subTitle) {
        NSAttributedString *attribute = [CommonUtil attributedStringWithHtml:subTitle];
        if (attribute && [attribute length] > 8) {
            NSMutableAttributedString *muAttribute = [[NSMutableAttributedString alloc] initWithAttributedString:attribute];
            [muAttribute replaceCharactersInRange:NSMakeRange(8,[attribute length]-8) withString:@"..."];
            _subLabel.attributedText = muAttribute;
        }else{
            _subLabel.attributedText = attribute;
        }
    }