UITextField限制輸入長度

因leader要求輸入長度做限制，而且要求一個漢字算2個字元，其他的算1個字元，再加上一個Controller有多個UITextFiled，是以我這麼寫控制長度。(也許會有更好的方法)

.m檔案

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UITextField *textF = [[UITextField alloc] initWithFrame:CGRectMake(10, 100, self.view.frame.size.width - 20, 30)];
    textF.layer.borderWidth = 0.5;
    textF.layer.borderColor = [UIColor lightGrayColor].CGColor;
    textF.layer.cornerRadius = 5;
    textF.layer.masksToBounds = YES;
    [self.view addSubview:textF];
    
    [textF addTarget:self action:@selector(textFieldChange:) forControlEvents:UIControlEventEditingChanged];
}

- (void)textFieldChange:(UITextField*)textF{
    
    if ([self calculateTextNumber:textF.text]>30) {
        float number = 0.0;
        NSString *str = [NSString string];
        for (float index = 0.0; index < textF.text.length;index++ ) {
            NSString *character = [textF.text substringWithRange:NSMakeRange(index, 1)];
            if ([character lengthOfBytesUsingEncoding:NSUTF8StringEncoding] == 3) {
                number += 2;
            } else {
                number += 1;
            }
            
            if (number > 30) {//30個字元 == 15個漢字
                break;
            }else{
                str = [str stringByAppendingString:character];
            }
            
        }
        
        textF.text = str;
        
    }
}

/**
 *  計算字元
 *
 *  @param textA 需要計算的字元串
 *
 *  @return 傳回字元數
 */
-(CGFloat)calculateTextNumber:(NSString *) text
{
    float number = 0.0;
    for (int index = 0; index < [text length]; index++) {
        NSString *character = [text substringWithRange:NSMakeRange(index, 1)];
        if ([character lengthOfBytesUsingEncoding:NSUTF8StringEncoding] == 3) {
            number += 2;
        } else {
            number += 1;
        }
    }
    return number;
}