Transferring focus from a textbox to a button

[gamer1127]

Jimmanuel wrote:

Why? Have you tried separate handlers for each control?

I just thought of applying the concept of having controls tagged to only one event-handler if they will have the same behavior. If that is the case, then i'll try using one event-handler for each control.

[gamer1127]

Your right about that. It is indeed the source of the problem. Thanks for that. :)

[gamer1127]

Now I have a new problem. Whenever I click the Log-In button it doesn't show an error message even if there's no entered data or the entered username and passwords are both wrong. It just do the event of logging in if both the username and passwords are correct. The username and password are saved in an MS Access database and i used SELECT query to check if both exists. Here is the code to clearly understand:

string sConnection = "Provider = Microsoft.Jet.OLEDB.4.0;" + "Data Source = Schedule.mdb";

        try
        {
            OleDbConnection dbConnect = new OleDbConnection(sConnection);
            dbConnect.Open();

            string sqlString = "SELECT \* FROM LogIn WHERE ID = '" + txtBoxLogIn.Text + "' AND Password = '" + txtBoxPassword.Text + "';";

            OleDbCommand dbCmd = new OleDbCommand();
            dbCmd.CommandText = sqlString;
            dbCmd.Connection = dbConnect;

            OleDbDataReader dbReader;
            dbReader = dbCmd.ExecuteReader();

            while (dbReader.Read())
            {
                if (dbReader\[0\].ToString() == txtBoxLogIn.Text && dbReader\[1\].ToString() == txtBoxPassword.Text )
                {
                    frmMainForm frmMainForm = new frmMainForm();
                    frmMainForm.ShowDialog();
                    this.Close();
                }
                else
                {
                    MessageBox.Show("Either the Username or Password does not exist", "Log-In Error", MessageBoxButtons.OKCancel, MessageBoxIcon.Error);
                }
            }
            
            dbReader.Close();
            dbConnect.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
            return;
        }

Did I do something wrong?

[Jimmanuel]

But they don't all have the same behaviour, they have similar behaviour. It's not a bad idea, but you have to abstract away all of the things from the handler that are specific for each control. You can actually do this pretty elegantly with one handler by using the Controls Tag property and the sender param of the handler. The idea is that the Enter key press transfers focus to the next Control, right? That's the similar behaviour the handler should implement but it needs to know which Control to transfer focus to. That's easy with the Tag. In the constructor of your form go through the similar behaving Controls and save a reference to the next Control that gets focus in the Tag:

txtBoxLogIn.Tag = txtBoxPassword; // give focus to the password box
txtBoxPassword.Tag = btnProceedLogIn; // give focus to the button
btnProceedLogIn.Tag = null; // set this to null to signify the end of the chain

Then your handler simplifies to this:

private void focusForwardingControl_KeyDown(object sender, KeyEventArgs e)
{
Control control = sender as Control;
if (control == null)
{
// if this event isn't from a Control object then return
return;
}

if (e.KeyCode == Keys.Enter)
{
    // get the next Control to have focus
    Control nextControl = control.Tag as Control;
    if (nextControl != null)
    {
        // if there's a valid Control stored then give it focus
        nextControl.Focus();
    }
}

}

Then both text boxes can use to the same event handler to forward focus to the next Control in the chain. Note that I'm using the KeyDown handler instead of KeyPress, I like the Event Args better. Also, all code here was written in the CP post editor so it hasn't been tested or compiled :)

:badger:

[gamer1127]

Ok. I'll try using this one and see if it works. :)

[Jimmanuel]

There are a couple things wrong: * This deserves a new post instead of a reply to your original question. * The reader and connection are not properly disposed of, they should be used in using statements to ensure that even if the Exception handler or this.Close() is called they get cleaned up properly. * Catching the general Exception is considered bad practice. * The case where dbReader.Read() returns false isn't handled - if there aren't any matching rows then the inner if - else will be skipped completely *** This is probably the cause of what you're seeing * SELECT * is also not the best practice, it'd be better if you specify the column names in the SELECT. * You should use a parameterized query to prevent SQL injection attacks. Here's and example for SqlConnections: clickety[^], OleDbConnections are similar * shouldn't that while be an if? * If those column values might be null then they should be checked for DBNull.Value before they're ToString()ed

:badger:

[gamer1127]

With all the things you pointed out, it means that I have to learn a lot of things when it comes to programming with relational database. :( Have to start reading all the ebooks that i got. We just started discussing programming with database and we already have a project that has it.

[Jimmanuel]

It's all forgivable if you're new :). The really important one in that list is to make sure that the connection to the database is cleaned up properly: see the docs for the OleDbConnection[^] class for a small example of how to protect your connection. For the details about what it's doing read up on the using[^] statement.

:badger:

[gamer1127]

Alright. Thanks for your answers. I think it will really help me a lot. :)

[Jimmanuel]

Glad to help :)

:badger:

[ragnaroknrol]

While a lot of folks will get mad at people "having others do their homework for them" you handled this very well. You attempted the code, had some problems and asked an intelligent question. You listened to advice, tried the solution and again did everything correct. You did your best and this stuff is not easy at all. Don't give up and keep going, with your attitude you can do it. :) Threads like these are part of why this place exists.