KeyPress event equivalent in WPF

i have the following code in WPA, and i am trying to convert it to WPF. I tried Keydown instead of Keypress and changed, for example,

(e.keyChar == '-') to (e.key == e.Subtract):

1. its not working the same
2. I cant find the equal sign within e.key

first code:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        foreach (TextBox tb in this.Controls.OfType<TextBox>())
        {
            tb.Enter += textBox_Enter;
        }
    }

    void textBox_Enter(object sender, EventArgs e)
    {
        focusedTextbox = (TextBox)sender;
    }

private void Form1_KeyPress(object sender, KeyPressEventArgs e)
    {

        if (e.KeyChar == '+')
        {
            operand1.Real = getOperand.Real;
            operand1.Imag = getOperand.Imag;
            flag1 = 1;
            e.Handled = true;
        }
        else if (e.KeyChar == '-')
        {

            if (focusedTextbox != null)
            {
                if (focusedTextbox.Text == "")
                {
                    e.Handled = false;
                }
                else
                {
                    e.Handled = true;
                    operand1.Real = getOperand.Real;
                    operand1.Imag = getOperand.Imag;
                    flag1 = 2;
                }
            }

        }
        else if (e.KeyChar == '*')
        {
            operand1.Real = getOperand.Real;
            operand1.Imag = getOperand.Imag;
            flag1 = 3;
            e.Handled = true;
        }
        else if (e.KeyChar == '/')
        {
            operand1.Real = getOperand.Real;
            operand1.Imag = getOperand.Imag;
            flag1 = 4;
            e.Handled = true;
        }
        else if (e.KeyChar == '=')
        {
            e.Handled = true;
            operand2.Real = getOperand.Real;
            operand2.Imag = getOperand.Imag;

            switch