iOS UITextField 限制输入长度，中英文混排，汉字占2个长度，英文数字占1个长度

产品有这样的需求

咋一看，比较简单，但涉及到中英混排就比较麻烦了，话不多说，上代码！

#import <UIKit/UIKit.h>

@interface UITextField (HL_LimitLength)
/** * 使用时只要调用此方法，加上一个长度(int)，就可以实现了字数限制,配合tools中的方法 可以支持汉字。汉字占2个长度 * * @param length */
- (void)limitTextLength:(int)length;
/** * uitextField 抖动效果 */
- (void)shake;
@end

//
// UITextField+HL_LimitLength.m
// HitLive
//
// Created by 王飞 on 16/4/8.
// Copyright © 2016年 国广星空视频科技（北京）有限公司. All rights reserved.
//

#import "UITextField+HL_LimitLength.h"

@implementation UITextField (HL_LimitLength)
static NSString *kLimitTextLengthKey = @"kLimitTextLengthKey";
- (void)limitTextLength:(int)length
{
    objc_setAssociatedObject(self, (__bridge const void *)(kLimitTextLengthKey), [NSNumber numberWithInt:length], OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    [self addTarget:self action:@selector(textFieldTextLengthLimit:) forControlEvents:UIControlEventEditingChanged];

}
- (void)textFieldTextLengthLimit:(id)sender
{
    NSNumber *lengthNumber = objc_getAssociatedObject(self, (__bridge const void *)(kLimitTextLengthKey));
    int length = [lengthNumber intValue];
    //下面是修改部分
    bool isChinese;//判断当前输入法是否是中文
    NSArray *currentar = [UITextInputMode activeInputModes];
    UITextInputMode *current = [currentar firstObject];
    //[[UITextInputMode currentInputMode] primaryLanguage]，废弃的方法
    if ([current.primaryLanguage isEqualToString: @"en-US"]) {
        isChinese = false;
    }
    else
    {
        isChinese = true;
    }

    if(sender == self) {
        // length是自己设置的位数
        NSString *str = [[self text] stringByReplacingOccurrencesOfString:@"?" withString:@""];
        if (isChinese) { //中文输入法下
// int chineseLength = length/2;
            UITextRange *selectedRange = [self markedTextRange];
            //获取高亮部分
            UITextPosition *position = [self positionFromPosition:selectedRange.start offset:0];
            // 没有高亮选择的字，则对已输入的文字进行字数统计和限制
            if (!position) {
// if ( str.length>=length) {
                int textcount = [Tools convertToInt:[self text]];
                if ([Tools convertToInt:[self text]] >= length) {
                    NSString *strNew = [NSString stringWithString:str];
                    int chineseCount = [[NSString stringWithFormat:@"%lu",textcount - str.length] intValue];

                    int indexCount = (length/2 -(textcount - 2*chineseCount)/2 )+ (textcount - 2*chineseCount);

                    [self setText:[strNew substringToIndex:indexCount]];
                }
            }
            else
            {
                // NSLog(@"输入的");

            }
        }else{
            if ([str length]>=length) {
                NSString *strNew = [NSString stringWithString:str];
                [self setText:[strNew substringToIndex:length]];
            }
        }
    }
}

- (void)shake
{
    CAKeyframeAnimation *keyAn = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    [keyAn setDuration:0.5f];
    NSArray *array = [[NSArray alloc] initWithObjects:
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x-5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x+5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x-5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x+5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x-5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x+5, self.center.y)],
                      [NSValue valueWithCGPoint:CGPointMake(self.center.x, self.center.y)],
                      nil];
    [keyAn setValues:array];

    NSArray *times = [[NSArray alloc] initWithObjects:
                      [NSNumber numberWithFloat:0.1f],
                      [NSNumber numberWithFloat:0.2f],
                      [NSNumber numberWithFloat:0.3f],
                      [NSNumber numberWithFloat:0.4f],
                      [NSNumber numberWithFloat:0.5f],
                      [NSNumber numberWithFloat:0.6f],
                      [NSNumber numberWithFloat:0.7f],
                      [NSNumber numberWithFloat:0.8f],
                      [NSNumber numberWithFloat:0.9f],
                      [NSNumber numberWithFloat:1.0f],
                      nil];
    [keyAn setKeyTimes:times];

    [self.layer addAnimation:keyAn forKey:@"TextAnim"];
}

@end

其中 工具类的convertToInt:方法如下
主要就是用计算string的长度 汉字2个长度，英文1个字符

+(int)convertToInt:(NSString*)strtemp {

    int strlength = 0;
    char* p = (char*)[strtemp cStringUsingEncoding:NSUnicodeStringEncoding];
    for (int i=0 ; i<[strtemp lengthOfBytesUsingEncoding:NSUnicodeStringEncoding] ;i++) {
        if (*p) {
            p++;
            strlength++;
        }
        else {
            p++;
        }
    }
    return strlength;

}