MDI Form & ChildForm (with Show Dialog)?

I has 4 form

1. Main.vb (IsMdiContainer = T)

2. Form1.vb (has textbox1 , Button1)

3. Form2.vb (Has button1)

4. Form3.vb ( has textbox1, button1)

i start with Main.vb, and show Form1.vb (

code :
dim frm1 as new Form1
frm1.MdiParent = Me
frm1.show()

at Frm1 i has 1 textbox (textbox1) and button1, if i clickk button1, form2 show with dialogform

at button1 click
form2.showdialog()

in form2, i has button1 if i click, form3 show with dialogform too

code
form3.showdialog()

in form3 i has textbox1. and button
if i clock button1. i'll put textbox1 value into form 1 textbox.
code : at button1 click.

form1.textbox1.text = me.textbox1.text

but the textbox1 in form1 not has value ?