How to return a value from a Form in C

Question

I have a main form  let s call it frmHireQuote  that is a child of a main MDI form  frmMainMDI   that shows another form  frmImportContact  via ShowDialog   when a button is clicked   When the user clicks the  OK  on frmImportContact  I want to pass a few string variables back to some text boxes on frmHireQuote   Note that there could be multiple instances of frmHireQuote  it s obviously important that I get back to the instance that called this instance of frmImportContact   What s the best method of doing this

User · Answer

I just put into constructor something by reference  so the subform can change its value and main form can get new or modified object from subform

User · Answer

Create some public Properties on your sub-form like so   public string ReturnValue1  get set    public string ReturnValue2  get set     then set this inside your sub-form ok button click handler  private void btnOk Click object sender EventArgs e        this ReturnValue1    Something       this ReturnValue2   DateTime Now ToString      example     this DialogResult   DialogResult OK      this Close        Then in your frmHireQuote form  when you open the sub-form  using  var form   new frmImportContact          var result   form ShowDialog        if  result    DialogResult OK                string val   form ReturnValue1               values preserved after close         string dateString   form ReturnValue2            Do something here with these values            for example         this txtSomething Text   val            Additionaly if you wish to cancel out of the sub-form you can just add a button to the form and set its DialogResult to Cancel and you can also set the CancelButton property of the form to said button - this will enable the escape key to cancel out of the form

User · Answer

I normally create a static method on form dialog  that I can call  This returns the success  OK-button  or failure  along with the values that needs to be filled in    public class ResultFromFrmMain        public DialogResult Result   get  set         public string Field1   get  set           And on the form   public static ResultFromFrmMain Execute          using  var f   new frmMain                var result   new ResultFromFrmMain              result Result   f ShowDialog              if  result Result    DialogResult OK                    fill other values                       return result             To call your form   public void MyEventToCallForm        var result   frmMain Execute       if  result Result    DialogResult OK           myTextBox Text   result Field1     or something like that

User · Answer

I use MDI quite a lot  I like it much more  where it can be used  than multiple floating forms   But to get the best from it you need to get to grips with your own events  It makes life so much easier for you   A skeletal example   Have your own interupt types     Clock  Stock and Accoubts represent the actual forms in   the MDI application  When I have multiple copies of a form   I also give them an ID  at the time they are created  then   include that ID in the Args class  public enum InteruptSource       IS CLOCK   0  IS STOCKS  IS ACCOUNTS     This particular event type is time based    but you can add others to it  such as document   based  public enum EVInterupts       CI NEWDAY   0  CI NEWMONTH  CI NEWYEAR  CI PAYDAY  CI STOCKPAYOUT      CI STOCKIN  DO NEWEMAIL  DO SAVETOARCHIVE     Then your own Args type  public class ControlArgs         MDI form source     public InteruptSource source   get  set          Interrupt type     public EVInterupts clockInt   get  set          in this case only a date is needed       but normally I include optional data  as if a C UNION type        the form that responds to the event decides if       the data is for it      public DateTime date   get  set          CI STOCKIN     public StockClass inStock   get  set         Then use the delegate within your namespace  but outside of a class  namespace MyApplication   public delegate void StoreHandler object sender  ControlArgs e     public partial class Form1   Form       your main form     Now either manually or using the GUI  have the MDIparent respond to the events of the child forms   But with your owr Args  you can reduce this to a single function  and you can have provision to interupt the interupts  good for debugging  but can be usefull in other ways too   Just have al of your mdiparent event codes point to the one function           calendar Friday    new StoreHandler MyEvents           calendar Saturday    new StoreHandler MyEvents           calendar Sunday    new StoreHandler MyEvents           calendar PayDay    new StoreHandler MyEvents           calendar NewYear    new StoreHandler MyEvents     A simple switch mechanism is usually enough to pass events on to appropriate forms

User · Answer

delegates are the best option for sending data from one form to another   public partial class frmImportContact   Form        public delegate void callback data string someData       public event callback data getData CallBack       private void button Click object sender  EventArgs e              string myData    Top Secret Data To Share         getData CallBack myData             public partial class frmHireQuote   Form        private void Button Click object sender  EventArgs e               frmImportContact obj   new frmImportContact          obj getData CallBack    getData             private void getData string someData                 MessageBox Show  someData

User · Answer

I raise an event in the the form setting the value and subscribe to that event in the form s  that need to deal with the value change

User · Answer

Found another small problem with this code    or at least it was problematic when I tried to implement it   The buttons in frmMain do not return a compatible value  using VS2010 I added the following and everything started working fine   public static ResultFromFrmMain Execute          using  var f   new frmMain                 f buttonOK DialogResult   DialogResult OK            f buttonCancel DialogResult   DialogResult Cancel             var result   new ResultFromFrmMain              result Result   f ShowDialog               if  result Result    DialogResult OK                    fill other values                       return result             After adding the two button values  the dialog worked great  Thanks for the example  it really helped

User · Answer

If you want to pass data to form2 from form1 without passing like new form sting  data     Do like that in form 1  using  Form2 form2  new Form2         form2 ReturnValue1    lalala      form2 ShowDialog        in form 2 add  public string ReturnValue1   get  set     private void form2 Load object sender  EventArgs e       MessageBox Show ReturnValue1       Also you can use value in form1 like this if you want to swap something in form1  just in form1   textbox Text  form2 ReturnValue1

User · Answer

First you have to define attribute in form2 child  you will update this attribute in form2 and also from form1 parent      public string Response   get  set      private void OkButton Click object sender  EventArgs e         Response    ok        private void CancelButton Click object sender  EventArgs e         Response    Cancel        Calling of form2 child  from form1 parent      using  Form2 formObject  new Form2              formObject ShowDialog           string result   formObject Response           to update response of form2 after saving in result       formObject Response               do what ever with result          MessageBox Show  Response from form2    result

[c#] How to return a value from a Form in C#?

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