Question

Well, I have a simple program that is writing to a Database. I am trying to add validation to the textbox like this,

private void textBox1_TextChanged(object sender, EventArgs e)
{
    try
    {
         if (textBox1.Text.Length < -1)
         {
             MessageBox.Show("Don't Leave this field blank!");
         }
    }
    catch
    {
         //todo
    }
} 

and My save to database code,

private void button1_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection("Server = DAFFODILS-PC\\SQLEXPRESS;Database=Library;Trusted_Connection=True;");
    SqlCommand sql1 = new SqlCommand("INSERT into Book VALUES('" + textBox1.Text + "' , '" + textBox2.Text + "','" + dateTimePicker1.Value.ToShortDateString() + "')", con);
     con.Open();
     sql1.ExecuteNonQuery();
     con.Close();
     this.bookTableAdapter.Fill(this.booksDataSet.Book);
     MessageBox.Show("Data Added!");
     this.Close();    
}

But still it is adding blank data to the database and strange thing is in the database I have not allowed null but still data is getting added. Any clues where I am wrong?

Answer 1

I don’t see you stopping the database to add empty content. You are validating on the textbox_textchanged event which will only validate the text when someone enters the data. You need to put the validation on button1’s click event like this:

    private void button1_Click(object sender, EventArgs e)
    {
        if(string.IsNullOrEmpty(textBox1.Text.Trim()))
        {
            MessageBox.Show("Null String !!!!!!!!");
            return;
        }
        SqlConnection con = new SqlConnection("Server = DAFFODILS-PC\\SQLEXPRESS;Database=Library;Trusted_Connection=True;");
        SqlCommand sql1 = new SqlCommand("INSERT into Book VALUES('" + textBox1.Text + "' , '" + textBox2.Text + "','" + dateTimePicker1.Value.ToShortDateString() + "')", con);
        con.Open();
        sql1.ExecuteNonQuery();
        con.Close();
        this.bookTableAdapter.Fill(this.booksDataSet.Book);
        MessageBox.Show("Data Added!");
        this.Close();

    }