Enable Button in WPF C # through a function

I have a form for filling some data with Textbox .

I have a class that has some validation functions for fields name, password, user for example. And in my Code Behind I just call the function that validates by passing the parameters to it. If each entered field is valid a string declared receives the value of ok .

I would like the end button after all the fields to be validated, the save button that is disabled is enabled.

See how I'm doing:

string validacaoImg = "";
private void txt_nome(object sender, TextChangedEventArgs e)
{
    string regex = "^[A-Za-záéíóúàâêôãõüçÁÉÍÓÚÀÂÊÔÃÕÜÇ ]+$";
    Funcao.validaCampos(regex, txtNome.Text, imgNome, validacaoImg);
}

private void txt_dtNascimento(object sender, SelectionChangedEventArgs e)
{
    string regex = @"\d{2,2}/\d{2,2}/\d{4,4}";
    Funcao.validaCampos(regex, txtNascimento.Text, imgNascimento, validacaoImg);
}

private void txt_usuario(object sender, TextChangedEventArgs e)
{
    string regex = "^[[email protected]]+$";
    Funcao.validaCampos(regex, txtUsuario.Text, imgUsuario, validacaoImg);
}

private void txt_senha(object sender, TextChangedEventArgs e)
{
    string regex = @"(?=.*[A-Z])(?=.*[a-z])(?=.*\d)[A-Za-z0-9].+$";
    Funcao.validaCampos(regex, txtSenha.Text, imgSenha, validacaoImg);
}

My class Função :

public static void validaCampos(string regex, string txt, Image img, string validacaoImg)
{
    TextBox texto = new TextBox();
    texto.Text = txt;
    img.Visibility = Visibility.Visible;
    Regex rx = new Regex(regex);
    if (texto.Text.Length > 0)
    {
        if (validaTextBoxes(txt, rx))
        {                        
            texto.BorderBrush = Brushes.Green;
            validacaoImg = "check";
            texto.ToolTip = null;
        }
        else
        {
            texto.BorderBrush = Brushes.Red;                    
            texto.ToolTip = "Fora do padrão!";
            validacaoImg = "errado";
        }
    }
    else
    {
        texto.BorderBrush = Brushes.Red;
        texto.ToolTip = "Este campo não pode ficar vazio!";
        validacaoImg = "errado";                
    }
    validarImagem(img, validacaoImg);
}

public static bool validaTextBoxes(string texto, Regex regex)
{
    bool isValid = regex.IsMatch(texto);

    if (isValid)
    {
        return true;
    }
    else
    {
        return false;
    }
}

public static void validarImagem(Image img, string validacaoImg)
{
    var path = System.IO.Path.Combine(Environment.CurrentDirectory, "Imagens/");
    var uri = new Uri(path + validacaoImg + ".jpg");
    BitmapImage bm = new BitmapImage(uri);
    img.Source = bm;
}