Event Handling between forms in C#

Edward Munya

I am dealing with 2 forms. A child form and a parent form.
I want to enable a textbox on a parent form immediately when a child form closes.
Below are codes and error messages I got. Please any idea would be appreciated.

public class ChildForm: Form
{
    public delegate SomeEventHandler(object sender, EventArgs e);
    public event SomeEventHandler SomeEvent;


}
The above code is for child form

and again below codes are for parent form:

public class ParentForm : Form
{
    frmCaptureFingerPrint child = new frmCaptureFingerPrint();
    child.SomeEvent += new EventHandler(this.HandleSomeEvent);

    public void HandleSomeEvent(object sender, EventArgs e)
    {
        this.textBox1.enabled=true;
    }
}
Please need your help
I get a error message that:

Cannot implicitly convert type 'System.EventHandler to CaisseSec....SomeEventHandler

5 Replies

Know the answer? Post it — somebody with the same question will find it here.

Hemant Srivastava13y ago
I forgot to tell...If the above suggestion works for you, please mark this answer as accepted. That will help others to refer.

Thanks,
Hemant
0
Hemant Srivastava13y ago
Create your ParentForm like this:

public partial class Parent : Form
    {
        ChildForm childForm = null;

        public Parent()
        {
            InitializeComponent();

            childForm = new ChildForm();
            childForm.SomeEvent += new SomeEventHandler(childForm_SomeEvent);

            textBox1.Text = "";
        }
        void childForm_SomeEvent(object sender, EventArgs e)
        {
            textBox1.Text = "Child Form Closed";
        }
        private void button1_Click(object sender, EventArgs e)
        {
            childForm.Show();
        }
    }
and childForm like this:
// delegate declration is defined outside of the class
public delegate void SomeEventHandler(object sender, EventArgs e);

    public partial class ChildForm : Form
    {
        //event is defined here
        public event SomeEventHandler SomeEvent;
        public ChildForm()
        {
            InitializeComponent();
        }
        private void Form2_FormClosed(object sender, FormClosedEventArgs e)
        {
            SomeEvent(sender, e);
        }
    }
When button is clicked on Parent form, child form is opend. See below:
and when child form is closed, a text box is loaded with some message on Parent Form through an event. See below:

Hope it would definetly help.. If you have still any issue let me know..
0
Vulpes14y ago
All the code should be placed in the parent form.

The following lines should be placed in some eventhandler such as a button_Click:

frmCaptureFingerPrint child = new frmCaptureFingerPrint();
child.FormClosed += new FormClosedEventHandler(this.ChildForm_Closed);

and should, of course, be followed by:

textBox1.Enabled = false; // unless disabled elsewhere
child.Show();

If it's not working, then it may be to do with how you've added the FormClosed eventhandler.

This should simply be typed (or pasted) in rather than added via the Visual Studio designer. If you try to do it using the latter, then you will end up with a handler which fires when the parent form (not the child form) is closed.
0
Edward Munya14y ago
Hi
Vulpes

Thanks for yr response but still it does not work.
I agree with you that it would be better to handle the predefined FormClosed event rather than defining my own.

I tried to use the codes you suggested

Now where exactly should I place these codes may be that is the reason it does not work and remember that textbox should be enabled
based on the event fired from another form.

Please your assistance shall be appreciated
0
Vulpes14y ago
Well, the reason for the error is that SomeEvent is of type ChildForm.SomeEventHandler rather than System.EventHandler. So this line:

child.SomeEvent += new EventHandler(this.HandleSomeEvent);

should be:

child.SomeEvent += new ChildForm.SomeEventHandler(this.HandleSomeEvent);

However, if you're wanting to enable the textbox when the child form closes it would be better to handle the predefined FormClosed event rather than defining your own.

You could then do:

public class ParentForm : Form
{
frmCaptureFingerPrint child = new frmCaptureFingerPrint();
child.FormClosed += new FormClosedEventHandler(this.ChildForm_Closed);

public void ChildForm_Closed(object sender, FormClosedEventArgs e)
{
this.textBox1.Enabled=true;
}
}

and no additional code would then be needed in the child form class.
0