How to set a specific text to every TEdit? - delphi

Question

I am super newbie and tried to write following code which sets every TEdit.Text to one mentioned in code
procedure TForm2.Button1Click(Sender: TObject);
var
i : integer;
Edit : TEdit;
begin
for i := 0 to Edit.ComponentCount - 1 do
begin
with Edit.Components[i] do
begin
Text := 'Done';
end;
end;
end;
What am I doing wrong ?

Answer 1

Here are the mistakes that I can see:
You never assign a value to Edit.
Typically the form owns all the components, and so a TEdit will have zero owned components.
Edit.Components[i] is of type TComponent which does not have a Text property. If your code compiles, then Text is actually that of the form. The lesson you should learn from this point is never to use with ever again.
You should solve this using code like this:
procedure TForm2.Button1Click(Sender: TObject);
var
i: Integer;
Edit: TEdit;
begin
for i := 0 to ComponentCount-1 do begin
if Components[i] is TEdit then begin
Edit := TEdit(Components[i]);
Edit.Text := 'Done';
end;
end;
end;
Note that here we are using ComponentCount and Components[] from the form itself. We have removed the evil with statement. And we have had to cast the component to a reference of type TEdit, after first using the is operator to check the type of the component.
This approach will work so long as the form owns all the edits found within it. However, if you create controls dynamically, or if you use frames or parented forms, then this approach, based on ownership via Components[] will not yield all the controls. In such more complex cases you would need to iterate using the parent/child relationship using ControlCount and Controls[].

Answer 2

What am I doing wrong? Just about everything. What I think you are trying to achieve is to put the same text in all TEdits on the form. So you need to go through all the components in TForm (not Edit!) and and check that each is really a Tedit, and if so assign the text. Like this:
procedure TForm2.Button1Click(Sender: TObject);
var
i:integer;
begin
for i := 0 to ComponentCount - 1 do
begin
if Components[ I ] is TEdit then
begin
(Components[ I ] as TEdit).Text := 'Done';
end;
end;
end;
As an aside - avoid using 'with'. It just cases ambiguity and confusion.

Answer 3

You could iterate over all child controls of the form, and if the current control is a TEdit, then you set its text. If the current control is a windowed control, it might have child controls of its own, and you need to redo same thing for this control. Hence, let's use recursion:
procedure SetAllEdits(AParent: TWinControl; const AText: string);
var
i: Integer;
begin
for i := 0 to AParent.ControlCount - 1 do
if AParent.Controls[i] is TCustomEdit then
TCustomEdit(AParent.Controls[i]).Text := AText
else if AParent.Controls[i] is TWinControl then
SetAllEdits(TWinControl(AParent.Controls[i]), AText);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
SetAllEdits(Self, 'test');
end;
There are other ways, like subclassing the edit control and having the new class respond to broadcasted messages.

Answer 4

Answer from D. Heffernan is already good, I'm trying to make it easier to understand for beginner.
In this code, we do "typecast" TEdit to TComponent by command: aEdit := TEdit(aComponent), because TEdit is inherited from TComponent.
What you get from iteration (for ...) is TComponent, not TEdit. You get TEdit by "typecast" it.
procedure TForm2.Button1Click(Sender: TObject);
var
i : Integer;
aComponent : TComponent;
aEdit : TEdit;
begin
for i := 0 to ComponentCount-1 do
begin
aComponent := Components[i];
if aComponent is TEdit then
begin
aEdit := TEdit(aComponent);
aEdit.Text := 'Done';
end;
end;
end;