Sharing data between two Forms

[babalipk]

I am new to this forum and this is my first post.

I am working on a C# project. General outline of the project is:

FORM 1 collects data as entered by the user (in text boxes, radio buttons, check boxes, numeric up-down controls etc) .

FORM 1 then does some calculations using this data and prepares a text message. I have a class created to do this job and updated Message is with the Class.

FORM 2 should take this text message and display it using a Rich text box.

User typically opens FORM 2 as and when it is needed to see the Message. User can kill/minimize FORM 2 . There is a button on FORM 1 to show FORM 2.

FORM 1 must update the FORM 2 whenever a new Message is generated provided FORM 2 is already instanced ( either showing or in minimized state.)

When FORM 2 is instanced by FORM 1 it must get the message from Form 1, so that upon instancing the FORM 2 shows the latest message from FORM 1.

I have coded something which worked , but I am a bit skeptical about the approach. Please guide me.

What I am doing is:

FORM 2 which displays the Message string, is instanced as:

public string messageIn;

public FORM2(string myMessage)
	messageIn = myMessaage; // input string to on FORM public variable

In FORM 2 I have a public method:

public  void ShowMessage(messageIn)

I call this ShowMessage in the form_load method:

private void FORM2_Load(object sender, EventArgs e)
        {
            ShowMessage(messageIn);
        }

In FORM 1 , have to call this ShowMessage in FORM 2 so that update message gets displayed on FORM 2.

There are two possibilities:

1> FORM 2 is not yet instanced : I shouldn't care to update it.
2> FORM 2 is already instanced.I must update FORM 2

So check that part first as:

bool IsOpen = false;
            foreach (Form f in Application.OpenForms)
            {
                if (f.Text == "FORM2")
                {
                    IsOpen = true;  // FORM found
                    break;
                }
            } // Loop to check next FORM
			
			// If FORM2 is already instanced then and then only update 
			// If FORM2 is not instanced , no need to update
            if (IsOpen == true) 
            {
				// FORM2 already instanced , OK to update it
                FORM2 f1 = (FORM2)Application.OpenForms["FORM2"];
                f1.ShowMessage(message);

            }

When user Clicks on the button on FORM 1 to view message, I check first the whether the form is already instance or not.
If it is there already, I call the the method in FORM 2 as shown above, else I instance the FORM 2 as:

FORM2 frm2 = new FORM2(message);// message goes as FORM2 constructor input argument
   
   frm2.Show();

I am a bit worried about using:

FORM2 f1 = (FORM2)Application.OpenForms["FORM2"];

Is it safe (legitimate)/ good practice or it might pose some potential problems later?

Or is there any better / clean way of doing this?

Regards

Babali

[Mitja Bonca]

You could you delegates and event. This is the simpliest way to do it.
You need any help?

[babalipk]

You could you delegates and event. This is the simpliest way to do it.
You need any help?

Yes , please..

(I have 3 more forms those also get updated like the FORM 2 mentioned above)

Regards

Babali

[skatamatic]

This is a simple example of how to do this with events/delegates:

In Form1:

//Declare the delegate that will point to the text-setting method
        public delegate void TextChangeHandler(object sender, string s);
        //Declare the event that is to be raised when the text changes
        public event TextChangeHandler TextChange;

        //This button raises the TextChange event
        private void button1_Click(object sender, EventArgs e)
        {
            TextChange(sender, textBox1.Text);
        }
        //This button adds a new Form2 to the project, and registers 
        //its text changing method to be called when the textchange event
        //occurs
        private void button2_Click(object sender, EventArgs e)
        {
            //Create the form, and using a CTOR set the initial text
            Form2 newForm = new Form2(textBox1.Text);
            //Add the textchanged event to the new form
            TextChange += new TextChangeHandler(newForm.TextChangedEvent);
            newForm.Show();
        }

In Form2:

//CTOR - takes a string to initialize the label
        public Form2(string s)
        {
            SetText(s);
        }
        //This is the event that handles the changed text event from Form1
        public void TextChangedEvent(object sender, string s)
        {
            SetText(s);
        }
        //This is the actual method that changes the text (in this case, a label) 
        private void SetText(string s)
        {
            label1.Text = s;
        }

This is my understanding of events, anyway (and it works). If I did something wrong, please feel free to correct me.