Passing Data Between Forms

Introduction

Some of you would have faced a scenario where you wanted to pass data from one form to another in WinForms. Honestly, I too had a similar problem (that's why I am writing this article!).

There are so many methods (How many? I don't know) to pass data between forms in windows application. In this article let me take four important (easiest) ways of accomplishing this.

1. Using constructor
2. Using objects
3. Using properties
4. Using delegates
   
    

Let us see all the above methods in detail in the following sections.

For a data to be passed between forms using any of the above methods, we need two forms and some controls. Let us start by following the below steps.

Step 1: Create new project and select windows application. This will create a default form as "Form1". We can use this form for sending data.

Step 2: Add a textbox and a button to the form.

Step 3: Add another windows form for receiving the data and to display it. Right click the project and select Add->Add Windows Form. Enter a name or use the default name "Form2.vb" and click ok button.

Step 4: Add a label to the second form to display the text from form1

The Constructor Approach

This could be the easiest method of all. A method is invoked whenever you instantiate an object. This method is called a constructor. Code a constructor for form2 class with one string parameter. In the constructor assign the text to the label's text property. Instantiate form2 class in form1's button click event handler using the constructor with one string parameter and pass the textbox's text to the constructor.

Follow the below steps.

Step 1: Code a constructor for form2 class as below 

Public Sub New(ByVal strTextBox As String)

    InitializeComponent()

    label1.Text = strTextBox

End Sub

Step 2: Instantiate form2 class in form1's button click event handler as below

Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles 

    btnSend.Click

    Dim frm As Form2 = New Form2(textBox1.Text)

    frm.Show()

End Sub

The Object Approach

Objects are reference types, and are created on the heap, using the keyword new. Here we are going to pass data using objects. The approach is simple; in form2 we are going to instantiate form1 class.

Then instantiate form2 in the button click event handler of form1. After this we are going to pass form1 object to the form2 using form2's form1 object. The last step is to invoke the form2 window by calling the form2's show method.

Follow the below steps:

Step 1: Change the access modifier for textbox in form1 to public 

Public Class Form1

    Inherits System.Windows.Forms.Form

    Friend WithEvents textBox1 As System.Windows.Forms.TextBox

End Class       

Step 2: In the button click event-handler add the following code.  

Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles 

    btnSend.Click

    Dim frm As Form2 = New Form2

    frm.frm1 = Me

    frm.Show()

End Sub

Step 3:  In form2.cs, instantiate form1 class 

Public Class Form2

    Inherits System.Windows.Forms.Form

    Public frm1 As Form1

End Class

Step 4: In Form2's Load method type cast the object (frm1) of form1 to Form1 and access form1's textbox and assign its text to label's text.  

Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles

    MyBase.Load

    label1.Text = CType(frm1, Form1).textBox1.Text

End Sub

The Properties Approach

Properties allow clients to access class state as if they were accessing member fields directly, while actually implementing that access through a class method. In this method we are going to add one property to each form. In form1 we are going to use one property for retrieving value from the textbox and in form2, one property to set the label's text property. Then, in form1's button click event handler we are going to instantiate form2 and use the form2's property to set the label's text.

Follow the below steps:

Step 1: Add a property in form1 to retrieve value from textbox. 

Private ReadOnly Property _textBox1() As String

    Get

        Return textBox1.Text

    End Get

End Property

Step 2: Add a property in form2 to set the labels' text  

Friend WriteOnly Property _textBox() As String

    Set(ByVal Value As String)

        label1.Text = Value

    End Set

End Property

Step 3: In form1's button click event handler add the following code.  

Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles 

    btnSend.Click

    Dim frm As Form2 = New Form2

    frm._textBox = _textBox1

    frm.Show()

End Sub     

The Delegates Approach

Technically, a delegate is a reference type used to encapsulate a method with a specific signature and return type. You can encapsulate any matching method in that delegate. Here we are going to create a delegate with some signature and assign a function to the delegate to assign the text from textbox to label.

Follow the below steps:

Step 1: Add a delegate signature to form1 as below  

Public Delegate Sub delPassData(ByVal text As TextBox)

Step 2: In form1's button click event handler instantiate form2 class and delegate. Assign a function in form2 to the delegate and call the delegate as below  

Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles      

    btnSend.Click

    Dim frm As Form2 = New Form2

    Dim del As delPassData = New delPassData(AddressOf frm.funData)

    'Dim del As delPassData = New delPassData(frm.funData)

    del(Me.textBox1)

    frm.Show()

End Sub

Step 3: In form2, add a function to which the delegate should point to. This function will assign textbox's text to the label.  

Public Sub funData(ByVal text As TextBox)

    label1.Text = text.Text

End Sub

Conclusion

These four approaches are very simple in implementing data passing between forms. There are also other methods available in accomplishing the same. Source code for the methods I stated above is given at the top for download. It is time for you to put your thinking cap and find other ways of doing this. Happy Coding!!!