当文本框中没有文本时如何禁用按钮？

Question

I need the buttons BtnCalculate and BtnMessageBox to be disabled when there is nothing in the TxtQuantity and TxtPrice Text boxes including when the program starts. Does anyone know how to do this? Obviously the "Quantity and price must not be empty" message will not be needed in the code anymore after changes are made. Thank you very much in advance. May be simple but IDK what I am doing.

Here is the CODE:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void BtnCalculate_Click(object sender, EventArgs e)
    {
        //declare Variables
        int intQuantity;
        Decimal decPrice;
        Decimal decTotal;
        //make sure quantity and price are the same
        // if string is null or empty retuern textbox

        Decimal TAX_RATE = 0.06m;
        if (OosTax.Checked == true)
            { TAX_RATE = 0.09m; }
        if ((TxtQuantity.Text.Trim().Length == 0 || (TxtPrice.Text == "")))
        { MessageBox.Show("Quantity and price must not be empty", "Calculator", MessageBoxButtons.OKCancel, MessageBoxIcon.Information, MessageBoxDefaultButton.Button2); }
        else
        {
            try
            {
                intQuantity = Int32.Parse(TxtQuantity.Text);
                decPrice = Decimal.Parse(TxtPrice.Text);
                decTotal = (intQuantity * decPrice) * (1 + TAX_RATE);
                LblMessage.Text = decTotal.ToString("C");
            }
            catch (Exception ex)
            { // Send Focus to Quantity
                TxtQuantity.Focus();
                TxtQuantity.SelectAll();
            }
        }
    }

    private void BtnMessageBox_Click(object sender, EventArgs e)
    {
        //declare Variables
        int intQuantity;
        Decimal decPrice;
        Decimal decTotal;
        string message = "Your Total Is: ";
        Decimal TAX_RATE = 0.06m;
        if (OosTax.Checked == true)
        { TAX_RATE = 0.09m; }
        //make sure quantity and price are the same
        // if string is null or empty retuern textbox

        if ((TxtQuantity.Text.Trim().Length == 0 || (TxtPrice.Text == "")))
        { MessageBox.Show("Quantity and price must not be empty", "Calculator", MessageBoxButtons.OKCancel, MessageBoxIcon.Information, MessageBoxDefaultButton.Button2); }
        else
        {
            try
            {
                intQuantity = Int32.Parse(TxtQuantity.Text);
                decPrice = Decimal.Parse(TxtPrice.Text);
                decTotal = (intQuantity * decPrice) * (1 + TAX_RATE);
                // Display Total Currency as
                MessageBox.Show(message + System.Environment.NewLine + decTotal.ToString("C"), "Chapter Two",
                    MessageBoxButtons.OKCancel, MessageBoxIcon.Information, MessageBoxDefaultButton.Button1);

            }
            catch (Exception ex)
            { // Send Focus to Quantity
                TxtQuantity.Focus();
                TxtQuantity.SelectAll();
            }

        }
    }

    private void BtnExit_Click(object sender, EventArgs e)
    {
        this.Close();
    }

    private void BtnClear_Click(object sender, EventArgs e)
    {
        LblMessage.Text = String.Empty;
    }
}

Answer 1

use TextChanged event on textbox

like this

    private void textBox1_TextChanged(object sender, EventArgs e)
    {
        button1.Enabled = (textBox1.Text.Length > 0);
    }

if you wish to do this on window loaded,

use

textBox1_TextChanged(null,null);

on loaded event

Answer 2

I would just write a method that sets the button enabled property based on the textbox text length of the two textbox controls, and then call it from the form Load event and the TextChanged event of the textboxes:

private void Form1_Load(object sender, EventArgs e)
{
    ButtonEnabler();
}

private void txtPrice_TextChanged(object sender, EventArgs e)
{
    ButtonEnabler();
}

private void txtQuantity_TextChanged(object sender, EventArgs e)
{
    ButtonEnabler();
}

private void ButtonEnabler()
{
    bool enabled = txtPrice.TextLength > 0 && txtQuantity.TextLength > 0;
    btnCalculate.Enabled = enabled;
    btnMessageBox.Enabled = enabled;
}