限制textField的仅支持数字输入与实时监控输入内容

1、实时监控输入框输入内容（通知方式）

发送通知

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textFieldChanged:) name:UITextFieldTextDidChangeNotification object:self.phoneField];

实现通知

//监控textField内容变化
- (void)textFieldChanged:(NSNotification *)notification{
    UITextField *textField = notification.object;
    
    //输入手机号判断
    if ([textField isEqual:self.phoneField]) {
        if (textField.text.length >= 11) {
            textField.text = [textField.text substringToIndex:11];
        }

    }

}

2、仅支持输入数字（代理方式）

#define kAlphaNum @"0123456789"

若密码输入框需要仅支持数字和字母，可把kAlphaNum设置为：

#define kAlphaNum @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    
    //判断使其不能输入非数字字符串
    NSCharacterSet *cs;
    cs = [[NSCharacterSet characterSetWithCharactersInString:kAlphaNum] invertedSet];
    NSString *filter = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
    BOOL basicTest = [string isEqualToString:filter];
    if (!basicTest) {
        return NO;
    }
    return YES;
}