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Easy way to find out which
properties should be set when creating components at run
time
One of the
greatest strengths of Delphi is the ability to visually design the
user interface of an application. This sometimes means that you
would be creating most parts of your programs at design time rather
than at run time as you go into different parts of your programs.
Generally speaking, you can reduce the amount of memory required to
run your program by creating memory hungry components at run time --
only when your application requires the functionality of those
components. Here's a simple example on how to create components
dynamically at run time (how to create a "TLabel" component at run time at 10,10 with the
caption "hello, world"):
procedure TForm1.Button1Click(Sender: TObject);
var
RunTimeLabel : TLabel;
begin
//
// create RunTimeLabel
//
RunTimeLabel := TLabel.Create( Self );
with RunTimeLabel do
begin
//
// let RunTimeLabel know
// that it's owned by Form1
//
// Since this code is inside
// TForm1, Self refers to Form1
//
Parent := Self;
// customize the label
Left := 10;
Top := 10;
Width := 90;
Caption := 'hello, world!';
end;
//
// RunTimeLabel will be
// automatically rleased when the
// form it's on (Form1) is freed.
//
// we don't have to manually free it
//
end;
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Listing #1
: Delphi code. Right click runtime.pas
to download. |
That was easy enough. The real question is how do you find out
exactly which properties (such as Top, Left, Width, etc., in the
above example) has to be set at run time to get the effects you
want. For example, if you drop a "TLabel" component on a form, you'll notice that
there are more than 20 properties listed in the "Object Inspector". Do you have to set all those
properties at run time if you create the component dynamically? The
answer is no; most properties have default values, so you only have
to set those properties that are required by the component and the
ones you want to change. Well, except for the "Parent" property -- you must almost always set
this property, usually to the form or component which your new
component will be placed on or become a child of.
Here's an easy way to find out which properties you must set at
run time:
- Create the component you're interested in creating at runtime,
during design time and customize it any way you want. For example,
let's say you created a "TLabel" component called "RunTimeLabel"
- Right click on the form and select "View as Text"
- You'll see a line that
reads:
object
RunTimeLabel: TLabel All properties and their
values listed in between the above line and the very next
end statement (starting at the same tab position) are the
properties you must set at run time, in order to recreate the
component as you see it during the design time.
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