如何禁用提交按钮，直到C＃中的文本框不为空？

Question

Can you teach me how to disable a button until all textboxes are not empty? In my design form login , I have 2 textboxes and 2 buttons. I want to disable the buttons until both textboxes are not empty.

Here is my code in a c# Windows application form:

 SqlConnection con = new SqlConnection(@"Data Source=ADMIN-\MSSQLSERVERR;Initial Catalog=Admin;Integrated Security=True");
    private void button1_Click(object sender, EventArgs e)
    {

        SqlDataAdapter sda = new SqlDataAdapter("Select USN From Admin where USN ='" + textBox1.Text + "'and Password ='" + textBox2.Text + "'", con);
        DataTable dt = new DataTable();
        sda.Fill(dt);


        if (dt.Rows.Count == 1)
        {
            this.Hide();
            Admin_Panel aa = new Admin_Panel(dt.Rows[0][0].ToString());
            aa.Show();
        }

        else 
        {
            MessageBox.Show("Please check your username and password");
            textBox1.SelectAll();
            textBox2.Text = "";
        }
        button1.Enabled = !string.IsNullOrWhiteSpace(textBox1.Text);
    }

    private void button2_Click(object sender, EventArgs e)
    {
        SqlDataAdapter sda = new SqlDataAdapter("Select USN From Admin where USN ='" + textBox1.Text + "'and Password ='" + textBox2.Text + "'", con);
        DataTable dt = new DataTable();
        sda.Fill(dt);


        if (dt.Rows.Count == 1)
        {
            this.Hide();
            Student aa = new Student(dt.Rows[0][0].ToString());
            aa.Show();
        }

        else
        {
            MessageBox.Show("Please check your username and password");
            textBox1.SelectAll();
            textBox2.Text = "";
        }


        button2.Enabled = !string.IsNullOrWhiteSpace(textBox1.Text);

    }

    private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
            e.Handled = true;
        base.OnKeyPress(e);


    }

I also tried this

button1.Enabled = !string.IsNullOrWhiteSpace(textBox1.Text);

... but when I had already put Username and Password in the textboxes, the 2 buttons were not enabled.

Answer 1

First set your buttons.Enabled property to false. Then add a TextChanged-Handler for both TextBoxes, where you check if both TextBoxes contain something.

The code of the handlers could look like this:

private void textBox1_TextChanged(object sender, EventArgs e)
{
    setButtonVisibility();
}

private void textBox2_TextChanged(object sender, EventArgs e)
{
    setButtonVisibility();
}

private void setButtonVisibility()
{
    if ((textBox1.Text != String.Empty) && (textBox2.Text != String.Empty))
    {
        button1.Enabled = true;
        button2.Enabled = true;
    }
    else
    {
        button1.Enabled = false;
        button2.Enabled = false;
    }
}

Answer 2

You'll want to monitor changes to the textboxes, in their Changed event, like:

private void textbox1_Change(object sender, EventArgs e)
{
    ConditionallyEnableSubmitButton();
}

private void textbox2_Change(object sender, EventArgs e)
{
    ConditionallyEnableSubmitButton();
}

private void ConditionallyEnableSubmitButton()
{
    button1.Enabled = (!string.IsNullOrWhiteSpace(textBox1.Text) ||   
                       !string.IsNullOrWhiteSpace(textBox2.Text));
}

Hint at no extra charge: give any control that you are going to reference programmatically a recognizable name, such as "btnSubmit", "txtbxUsername", "txtbxPwd" etc.

You could do a lot worse than to read Steve McConnell's "Code Complete" for this and many other nudges toward good practice.

Answer 3

private void textbox1_TextChanged(object sender, EventArgs e)
{
    EnableButton();
}

private void textbox2_TextChanged(object sender, EventArgs e)
{
    EnableButton();
}

private void  EnableButton()
{
    if(textbox1.Text == "" || textbox2.Text == "")
    {
        button1.Enabled = false;
        button2.Enabled = false;
    }
    else
    {
        button1.Enabled = true;
        button2.Enabled = true;
    }
}