iOS 限制輸入框中文和英文混雜字符串長度

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

//UITextField 添加target監聽事件
- (void)handleTextFieldEditAction:(UITextField *)textField {
    NSString *lang = [textField.textInputMode primaryLanguage];
    if ([lang isEqualToString:@"zh-Hans"]) {
        UITextRange *selectedRange = [textField markedTextRange];
        UITextPosition *position = [textField positionFromPosition:selectedRange.start offset:0];
        if (!position) {
            if (textField.text.length >20) {
                textField.text = [textField.text substringToIndex:20];
            }
        }
    }else{
        if (textField.text.length >=20) {
            textField.text = [textField.text substringWithRange:NSMakeRange(0, 20)];
        }
    }
}

#pragma mark --UITextFieldDelegate
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    if ([string isValidateNickName] || string.length == 0) {
        return YES;
    }
    return NO;
}

//正則表達式允許輸入中英文,中劃線,下劃線
-(BOOL)isValidateNickName
{
    if (self.length == 0) {
        return NO;
    }
    NSString *regex = @"^[a-zA-Z0-9_\\-\u4e00-\u9fa5]+$";
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF MATCHES %@",regex];
    if ([pred evaluateWithObject:self]) {
        return YES;
    }
    return NO;
}

效果圖: