c# - how to pass data from a form to another form that is previously instantiated from any other form? -

i have 3 forms(form1,form2,form3), main form form1, opened form2 taking data , have update button on form2 take me form3, want whatever user writes on form3 updated form2, how can make possible using c#.net?

(i opened form2,form3 using showdialog() method)

//reference form2 form2 secondaryform = new form2(mainform);<br/> secondaryform.showdialog();  //in constructor of form2 save reference of form1 form1 form1 = null  form2(form1 mainform) {     form1 = mainform; }  //then instead of creating new mainform again use reference of form1  form1.updatetext(data); this.close() 

i have used above code getting nullreference exception on form1.updatetext(data);

just pass form 2 reference form 3 while instantiating it.. did form1 while opening form2. form3 use form2 reference call updatetext method should public method on form2

here code 3 forms, can update form others, have made can access form1 , form2 in form3.

using system; using system.linq; using system.text; using system.windows.forms;  namespace windowsformsapplication1 {     public partial class form1 : form     {         public  form2 frm2;         public  form3 frm3;          public form1()         {             initializecomponent();         }          private void form1_load(object sender, eventargs e)         {          }          public void updatetext()         {             this.textbox1.text = "";         }          private void button1_click(object sender, eventargs e)         {             if (frm2 == null)                 frm2 = new form2(this);                  frm2.showdialog();         }     } }   using system; using system.text; using system.windows.forms;  namespace windowsformsapplication1 {     public partial class form2 : form     {         public form1 reftoform1;          public form2(form1 f1)         {             reftoform1 = f1;             initializecomponent();         }          private void button1_click(object sender, eventargs e)         {             if (reftoform1.frm3 == null)                 reftoform1.frm3 = new form3(this);              reftoform1.frm3.showdialog();         }          public void updateform2(string txt)     {         this.textbox1.text = txt;     }      } }  using system; using system.linq; using system.text; using system.windows.forms;  namespace windowsformsapplication1 {     public partial class form3 : form     {         form2 reftoform2;         public form3( form2 f2)         {             reftoform2 = f2;             initializecomponent();         }          private void button1_click(object sender, eventargs e)         {             //pass data form1;             reftoform2.reftoform1.updatetext();              //pass data form2             reftoform2.updateform2("from form3");         }     } }