Как объединить два условия?

        private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            TextBox box = sender as TextBox;
            this.SendButton.IsEnabled = box.Text.Length > 0;
        }
 
 
 
        private void PasswordBox_PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox box = sender as PasswordBox;
            this.SendButton.IsEnabled = box.Password.Length > 0;
        }

if(textBox1.Text!=null && passwordBox1!=null)
{
 this.SendButton.IsEnabled = true;
}

        private void TextBox_TextChanged(object sender, TextChangedEventArgs e) 
        {
            if(login_txt.Text!=null && password_txt!=null)
           { 
              this.SendButton.IsEnabled = true;
           }
        }

        private void TextBox_TextChanged(object sender, TextChangedEventArgs e) 
        {
            TextBox box = sender as TextBox;
            this.SendButton.IsEnabled = box.Text.Length > 0;
        }
 
 
 
        private void PasswordBox_PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox box = sender as PasswordBox;
            this.SendButton.IsEnabled = box.Password.Length > 0;
        }

public Form1()
        {
            InitializeComponent();
            textBox1.TextChanged += new System.EventHandler(textBox1_TextChanged);
            textBox2.TextChanged += new System.EventHandler(textBox1_TextChanged); 
        }
.......
private void textBox1_TextChanged(object sender, EventArgs e)
        {
            if (textBox1.Text != string.Empty && textBox2.Text != string.Empty)
            {
                button11.Enabled = true;
            }
            else
            {
                button11.Enabled = false;
            }
        }

bool HasLoginPassword
{
   get { return login_txt.Text.Length > 0 && password_txt.Password.Length > 0; }
}
 
        private void TextBox_TextChanged(object sender, TextChangedEventArgs e) 
        {
           SendButton.IsEnabled = HasLoginPassword;
        }
 
 
 
        private void PasswordBox_PasswordChanged(object sender, RoutedEventArgs e)
        {
           SendButton.IsEnabled = HasLoginPassword;
        }