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More of this Feature • Page 1: Finding out how a modal form was closed • Page 3: Moving records of data between two forms

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Related Resources • A Beginner's Guide to Delphi Programming.TOC • Delphi Project file (dpr) • Working with forms • Delphi forms - Life Cycle

Now, knowing whether the user wants to accept or reject what occurred on the child form, the calling form can react by using the information from the child form or ignoring it. Let's see how...

Events to look at for ModalResult (in Forms.pas):

function TCustomForm.ShowModal: Integer;
procedure TCustomForm.CloseModal;
function TCustomForm.CloseQuery: Boolean;
procedure TCustomForm.Close;

ModalResult Constants from Controls.pas

const
  mrNone = 0;
  mrOk = idOk;
  mrCancel = idCancel;
  mrAbort = idAbort;
  mrRetry = idRetry;
  mrIgnore = idIgnore;
  mrYes = idYes;
  mrNo = idNo;
  mrAll = mrNo + 1;
  mrNoToAll = mrAll + 1;
  mrYesToAll = mrNoToAll + 1;

Sometimes you will need to get more than one piece of information back from a form, but let's start simple. The following example shows how to get the value stored in a TEdit (Name : 'Edit1') Text property if the user pressed the Ok button on the child form (Name: 'frmSimpleString').

// Code for main form
procedure TfrmMain.ModalResultdemo2Click(Sender: TObject);
var
  f:TfrmSimpleString ;
begin
  f := TfrmSimpleString.Create(nil);
  try
    if f.ShowModal = mrOk then
    ShowMessage(f.Edit1.Text);
  finally
    f.Release;
  end;
end;

To keep the example short we are just checking for an Ok response and ignoring negative responses. When the user presses the OK button (its ModalResult is set to mrOk) the following code reads the value of an edit control, Edit1, on the called form and then destroys the form. In a real application you might need information from several components on the called form. We could have streamlined the code a little more by adding code to let the user choose whether to continue with closing the form or aborting back into the called form:

// Code for main form
procedure TfrmMain.ModalResultdemo2Click(Sender: TObject);
var
  f:TfrmSimpleString ;
  S:String ;
begin
  f := TfrmSimpleString.Create(nil);
  try
    f.GetThatString(S);
    ShowMessage(s);
  finally
    f.Release;
  end;
end;

 
// Code for the called (child) form

type
TfrmSimpleString = class(TForm)
  Button1: TButton;
  Button2: TButton; 
  Edit1: TEdit;

private
{ Private declarations }
public
{ Public declarations }
  procedure GetThatString(var aString: string);
end;

var
  frmSimpleString: TfrmSimpleString;

implementation

{$R *.DFM}

procedure TfrmSimpleString.GetThatString(var aString: string);
begin 
  case ShowModal of
    mrOk: aString := 'OK' ;
    mrCancel: aString := 'Cancel' ;
  end;
end;

end.

On the called form we add a procedure GetThatString to interrogate the user modally to find out whether the user wants to continue or abort the current operation. For elegance, the Case statement is used rather than a chain of nested IF..THEN..ELSE statements, i.e.

If ShowModal = mrOk then
...
else if ShowModal = mrCancel then
... 
else if ShowModal = mrRetry then
...

Retrieving a string is simple enough but, often, you will need much more than a simple string. Methods for getting a lot of information back from a called form include using an array, a TList, a StringList, or records. The logic used to determine if the user wants to return information remains the same, only the means of storing it varies. To show how this might be done, I will use a record to store user input for retrieval once the user presses OK in the called form. To make things interesting, we will use an array of records so that multiple pieces of information can be returned from the called form!

Before digging into an example, lets go through a short lesson of record types for those programmers that may have not worked with records: "Records in Delphi".

Next page > Moving records of data between two forms > Page 1, 2, 3

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