Summary

This is a introduction of caculating or limiting text word counts.
The text is divided into DBC case charaters and SBC case charaters.
本文介绍全角字符和忽略全角字符的文本字数统计或限制。

Tip

• Editting in UITextField,these codes should be use for the protocol method
  “- (BOOL)textField:(UITextField )textField shouldChangeCharactersInRange:
  (NSRange)range replacementString:(NSString )string”,while UITextView is
  “- (BOOL)textView:(UITextView )textView shouldChangeTextInRange:(NSRange)range
  replacementText:(NSString )text”.

• 在UITextField和UITextView编辑时，以下代码分别用在其”输入许可”的代理方法shouldChangeCharactersInRange
  和shouldChangeTextInRange中。

DBC case (Half-width) characters

• Considering NSString objctive’s length,such as string.length, as word counts.
  不考虑全角字符

    if (range.location >= wordCount && string.length) {
        return NO;
    }else if (string.length + range.location > wordCount) {
        textField.text = [textField.text stringByAppendingString:[string substringToIndex:wordCount - range.location]];
        return NO;
    }
    return YES;

SBC case (Full-width) charaters

• A Full-width charater is counted two byte,a Half-width charater is counted one
  byte.
  区分全角、半角计算文本字数。
  The limitCount is a const integer value which is the max count that user can input.
  limitCount是允许用户输入的最大字数。

    if (!text.length) {//backspace
        return YES;
    }
    int count = [self wordCountWithText:[textView.text stringByAppendingString:text]];//charater counts
    if (count >= limitCount) {
        count = limitCount - [self wordCountWithText:textView.text];//The remaining words
        textView.text = [textView.text stringByAppendingString:[text substringToIndex:count / 2]];
        _lbCount.text = @"0";
        return NO;
    }
    return YES;

- (int)wordCountWithText:(NSString*)text {
    if (!text || !text.length) {
        return 0;
    }
    int length = 0;
    char *point = (char*)[text cStringUsingEncoding:NSUnicodeStringEncoding];
    NSUInteger lengthEncode = [text lengthOfBytesUsingEncoding:NSUnicodeStringEncoding];
    for (NSUInteger index = 0; index < lengthEncode; index++) {
        if (*point) {
            length++;
        }
        point++;
    }
    return length;
}

• Another way below is caculating for the Full-width charaters count:
  下面的方法是计算包含全角字符的文本字数：

#import "RegexKitLite.h"

- (int)calcStrWordCount:(NSString *)str {
    int nResult = 0;
    NSString *strSourceCpy = [str copy];
    NSMutableString *strCopy =[[NSMutableString alloc] initWithString: strSourceCpy];
    NSArray *array = [strCopy componentsMatchedByRegex:@"((news|telnet|nttp|file|http|ftp|https)://){1}"
    "(([-A-Za-z0-9]+(\\.[-A-Za-z0-9]+)*(\\.[-A-Za-z]{2,5}))|([0-9]{1,3}(\\.[0-9]{1,3}){3}))(:[0-9]*)"
    "?(/[-A-Za-z0-9_\\$\\.\\+\\!\\*\\(\\),;:@&=\\?/~\\#\\%]*)*"];
    if ([array count] > 0) {
        for (NSString *itemInfo in array) {
            NSRange searchRange = {0};
            searchRange.location = 0;
            searchRange.length = [strCopy length];
            [strCopy replaceOccurrencesOfString:itemInfo withString:@" " options:NSCaseInsensitiveSearch range:searchRange];
        }
    }

    char *pchSource = (char *)[strCopy cStringUsingEncoding:NSUTF8StringEncoding];
    int sourcelen = strlen(pchSource);

    int nCurNum = 0; //current word count
    for (int n = 0; n < sourcelen; ) {
        if( *pchSource & 0x80 ) {
            pchSource += 3; // NSUTF8StringEncoding encoding Chinese words is counted as 3 bytes
            n += 3;
            nCurNum += 2;
        }
        else {
            pchSource++;
            n += 1;
            nCurNum += 1;
        }
    }
    //the last word that insuffices one is calculated for one
    nResult = nCurNum / 2 + nCurNum % 2;  

    [strSourceCpy release];
    [strCopy release];
    return nResult;
}

The limit word count codes above compatible with users’ paste action.
以上限制字数代码在用户粘贴时也有效。

编写本博客相关环境：Mac OS 10.11.3，Mou 0.8.7，Xcode 7.2 (7C68)，iOS 9.2

转自大彬的 iOS开发 输入字数计算、限制

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