How to avoid using GlobalVars in components development?

[elGringo]

Ok, to demonstrate problem, I have following structure (pic №1 in Attachment)

 

-SomeComponent.bpl

    -uSomeComponent_BPL.pas

    -uAdditional.pas

 

-TestProgram.exe

  -uTestProgram.pas

 

 

In uSomeComponent_BPL.pas I have special published property SomeField (Pic №2 in Attachment)

...
property SomeField:string read FSomeField write FSomeField;
...

What is my problem and my Task?

 

When user will enter Some Value in SomeField I need to transfer and use it in unit uAdditional of component. I cannot do that without using GlobalVars for the moment.

 

What did I try?

 

After register of Component, I tried to Create Locally exemplar of TSomeComponent from uSomeComponent_BPL like this

 

uAdditional...

procedure TfAdditional.FormCreate(Sender: TObject);

var SomeComponent:TSomeComponent;

begin
    SomeComponent:=TSomeComponent.Create(Self);
    ShowMessage(SomeComponent.SomeField);


end;

In uSomeComponent_BPL.pas

procedure TSomeComponent.CreateAdditionalForm;

var AdditionalForm:TfAdditional;

begin

    AdditionalForm:=TfAdditional.Create(Self);

end;

Added component to form in test program. Then in object inspector I entered some test value like '123'. After that in test program I tried to call that externally like this

procedure TfMainform.SomeComponent1Click(Sender: TObject);
begin
SomeComponent1.CreateAdditionalForm;
end;

But message was emty - so that didn't work...

 

If to use Global Vars - everything will work. But it is known that GlobalVars - bad practice. 

 

Conclusion

 

If you know how to transfer data from unit to unit in that case, please help me.

Regards, Stanislav. 

324_GlobalVarTest.zip

[gatosoft]

Hi ElGringo,

Firts to all, sorry for my english, i'll try to explain me.

1) You have a component into your Test Program... this INSTANCE is named SomeComponent1 and his SomeValue property its set to "123"
2) When you call the CreateAdditionalForm Method, you delcare a new variable of TSomecomponent class, and you INSTANCES A NEW OBJECT
3) When you call ShowMessage, you pass the New INSTANCE recently created, which SomeValue property is empty.

I suggest:

1) Delete the OnCreate Method from your TAdditional Form
2) Create a New Private variable FSomeComponent
3) Create a overload constructor for this form,like this:
 

  TfAdditional = class(TForm)
  private
    { Private declarations }
    FSomeComponent: TSomeComponent;
  public
    { Public declarations }
    Constructor Create(aSomeComponent: TSomeComponent);
  end;

 
4) Implement it, like this:
 

constructor TfAdditional.Create(aSomeComponent: TSomeComponent);
begin
  inherited Create(Application);
  FSomeComponent:= aSomeComponent;
  ShowMessage(FSomeComponent.SomeField);
end;

 

In this way, when you creates this Form, pass the Component "parent"

5) Finally, into the CreateAdditionalForm method write this:

procedure TSomeComponent.CreateAdditionalForm;

var AdditionalForm:TfAdditional;

begin

    AdditionalForm:=TfAdditional.Create(Self);

end;

I hope I have understood and solved your problem,

 

(again, sorry for my english)

Bye

Gatosoft

[elGringo]

Hi, gatosoft! Yes! your answer is 100 % of what I need for the moment !!!

 

Yesterday i found a little bit different decision, but yours is more elegant.

 

My decision was lite that

 

uSomeComponent_BPL

procedure TSomeComponent.MyClick(Sender: TObject);
begin


  fAdditionalLocal:=TfAdditional.Create(Self);
  fAdditionalLocal.somefieldInternal:=Self.SomeField;

  ShowMessage(fAdditionalLocal.somefieldInternal);

end;

but it is not so convenient as yours one!!! Thank you again.