How to set MaxLength in PasswordBox when input is Button.Content instead of keyboard? (WPF)

Question

I have a simple keypad with 0-9, a Clear button, and an Enter Button. Clicking the numbers places the content into a PasswordBox. Clicking the Clear button simulates a backspace, and the Enter Button acts as a submit for predefined 4 digit codes. If the correct code is entered, it appends to a textbox showing that access was granted, else, access denied.

I am having no problems except when trying to set a MaxLength on the PasswordBox. I have tried it in my XAML with:

<PasswordBox PasswordChanged="securityCodeTextBox_PasswordChanged" MaxLength="4" KeyDown="securityCodeTextBox_KeyDown" x:Name="securityCodeTextBox" PasswordChar="•" HorizontalAlignment="Left" Margin="117,20,0,0" VerticalAlignment="Top" Height="23" Width="213"/>

I've also tried it programmatically with:

securityCodeTextBox.MaxLength = 4;

This is the only code in my function for the numeric buttons:

private void ButtonClickNum(object sender, RoutedEventArgs e)
    {
        Button button = (Button)sender;

        securityCodeTextBox.Password += button.Content.ToString();
    }

I don't have to implement this, since if the code is wrong, it will just log "Access Denied" in the textbox below it. However, I am really curious on how to do this after realizing the MaxLength is for keyboard input, not button clicks. I currently have the keyboard completely disabled with:

//Prevent keyboard input

    private void securityCodeTextBox_KeyDown(object sender, KeyEventArgs e)
    {
        e.Handled = true;
    }

Next attempt

I created a very sloppy way to disable all but the Clear and Enter buttons if the length reaches >=4 with these code snippets in the Num and Clear Button Click functions:

private void ButtonClickNum(object sender, RoutedEventArgs e)
    {
        Button button = (Button)sender;

        securityCodeTextBox.Password += button.Content.ToString();

        //Disable all buttons if MaxLength is reached

        if(securityCodeTextBox.Password.Length >= 4)
        {
            button0.IsEnabled = false;
            button1.IsEnabled = false;
            button2.IsEnabled = false;
            button3.IsEnabled = false;
            button4.IsEnabled = false;
            button5.IsEnabled = false;
            button6.IsEnabled = false;
            button7.IsEnabled = false;
            button8.IsEnabled = false;
            button9.IsEnabled = false;
        }

    }

Clear Button

    /**
     * Remove(int startIndex, int count) startIndex = position, count = num of chars to delete
     */
    private void ButtonClickClear(object sender, RoutedEventArgs e)
    {

        if (securityCodeTextBox.Password.Length > 0)
        {
            securityCodeTextBox.Password = securityCodeTextBox.Password.Remove(securityCodeTextBox.Password.Length - 1, 1);
        }
        //Enable all the buttons again once password is less than MaxLength

        if (securityCodeTextBox.Password.Length < 4)
        {
            button0.IsEnabled = true;
            button1.IsEnabled = true;
            button2.IsEnabled = true;
            button3.IsEnabled = true;
            button4.IsEnabled = true;
            button5.IsEnabled = true;
            button6.IsEnabled = true;
            button7.IsEnabled = true;
            button8.IsEnabled = true;
            button9.IsEnabled = true;
        }
    }

Is there a cleaner way to implement the MaxLength method when the input is the content of a button?

Answer 1

I never worked with WPF or password input Controls before, but I would try it like this, it just wont add up the password if the length is reached.

    private void ButtonClickNum(object sender, RoutedEventArgs e)
    {
        Button button = (Button)sender;

        if(securityCodeTextBox.Password.Length < 4)
            securityCodeTextBox.Password += button.Content.ToString();             
    }