如何从vb.net的另一个表单中检查表单1的复选框？

Question

I have two forms, form 1 and form 2 (windows application). How can i access and check a checkbox in form 1 from form 2. Initially i tried calling the form name and then the control like form1.chkCanada.checked = true , it did not work. And then i added a property in form 1

Public Property abc As Boolean
    Get
        Return chkCanadianStmtInd.Checked
    End Get
    Set(value As Boolean)
        chkCanadianStmtInd.Checked = value
    End Set
End Property

and then in form 2

Dim frm As New frm1
frm.abc = True  'Checked

And it still doesnt work. Am i missing anything here?

Answer 1

Consolidating comments here:

In order to access controls on a form that shows another form to the user you have two options, if no interaction is needed with the first form while the second form is active you can use showdialog and do all of your logic after the second form has closed, if you ned to maintain the ability to interact with the first form while the second is still open then you need to use custom events.

Showdialog:

The simpler of the two options is to switch your form.show() function calls to form.showdialog() . This effectively tells the first form that it should stop processing at the form.showdialog() line and wait for the child form to close before proceeding. Once the second form is closed the first form will pick up where it left off and that would be where any processing that relies on the values of the second form would take place.

Custom Events:

If you want to allow the user to interact with both the first and second forms at the same time then you will need to use custom events. In order to do this you will need three things. The custom event, a raiseevent call and an event handler.

So in your Form2 class you will need to declare the custom event. In this case since you are trying to check(or uncheck I assume) a box your custom event declaration will look like:

public event ChangeCheckedValue(byref state as boolean)

Now on your button click event you will need to raise the event to the handler on Form1:

RaiseEvent ChangeCheckedValue(booleanValue)

Now that those statements are in place you will need to changed your form2 object that is being shown by Form1. What I normally do is make Form2 a form wide variable on Form1 and declare it like:

private withevents frm as Form2

Once you have the frm variable in your Form1 class you can add a handler for the ChangeCheckedValue event:

protected sub HandleCheckChanged(byref bln as boolean) handles frm.ChangeCheckedValue
    'Set the checked state of your checkbox.
End sub

Once you have all that set up you should see what you expect.

Answer 2

Alternatively you can pass a handle of form1 to form2 constructor

Form1:

Public Class Form1

  Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
    Dim _form2 As New Form2(Me)

    _form2.Show()
  End Sub
End Class

Form2:

Public Class Form2

  Public Sub New(ByVal _form1 As Form1)

    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    _form1.CheckBox1.Checked = True

  End Sub


End Class