UITextField限制输入文字

一、viewDidLoad时监听通知

 NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
    [center addObserver:self selector: @selector(textFiledEditChanged:)
                   name:@"UITextFieldTextDidChangeNotification"
                 object:self.demand_nameField];

二、销毁通知

#pragma mark - life cycle
- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

三、实现通知监听的方法

#pragma mark - 监听UITextField文本变化
-(void)textFiledEditChanged:(NSNotification *)obj{
    UITextField *textField = (UITextField *)obj.object;
    
    NSString *toBeString = textField.text;
    NSArray *currentar = [UITextInputMode activeInputModes];
    UITextInputMode *current = [currentar firstObject];
    if ([current.primaryLanguage isEqualToString:@"zh-Hans"]) { // 简体中文输入，包括简体拼音，健体五笔，简体手写
        UITextRange *selectedRange = [textField markedTextRange];
        //获取高亮部分
        UITextPosition *position = [textField 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 (toBeString.length > MAX_LIMIT_NUMSField) {
                [self showHudTipStr:@"超出了限制"];
                
                textField.text = [toBeString substringToIndex:MAX_LIMIT_NUMSField];
            }
        }
        // 有高亮选择的字符串，则暂不对文字进行统计和限制
        else{
            
        }
    }
    // 中文输入法以外的直接对其统计限制即可，不考虑其他语种情况
    else{
        if (toBeString.length > MAX_LIMIT_NUMSField) {
            [self showHudTipStr:@"超出了限制"];
            textField.text = [toBeString substringToIndex:MAX_LIMIT_NUMSField];
        }
    }  
}