LCL Tips/fr

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Create controls manually without overhead

Set the Parent as last

Pour les utilisateurs de Delphi: A la différence de Delphi la bibliothèque LCL permet de paramétrer presque toutes les propriétés dans n'importe quel ordre. Par exemple sous Delphi vous ne pouvez pas placer un contrôle sans un parent . La bibliothèque LCL permet ceci et cette fonctionnalité peut être employée pour réduire du calcul supplémentaire(overhead).

<delphi>

 with TButton.Create(Form1) do begin
   // 1. creating a button sets the default size
   // 2. change position. No side effects, because Parent=nil
   SetBounds(10,10,Width,Height);
   // 3. change size depending on theme. Not yet, because Parent=nil
   AutoSize:=true;
   // 4. changing size because of AutoSize=true. Not yet, because Parent=nil
   Caption:='Ok';
   // 5. Set Parent. Now all the above takes place, but in a single action.
   Parent:=Form1;
 end;

</delphi> When a control has a Parent, then all properties take effect immediately. Without a Parent many properties do nothing more than store the value. And as soon as the Parent is set every property is applied. This is especially true for grand children:

 GroupBox1:=TGroupBox.Create(Self);
 with GroupBox1 do begin
   with TButton1.Create(Self) do begin
     AutoSize:=true;
     Caption:='Click me';
     Parent:=GroupBox1;
   end;
   Parent:=Form1;
 end;
 Form1.Show;

Autosizing starts not before every parent is setup and the form becomes visible.

Avoid early Handle creation

As soon as the Handle of a TWinControl is created, every change of a property changes the visual thing (called the widget). Even if a control is not visible, when it has a Handle, changes are still expensive.

Use SetBounds instead of Left, Top, Width, Height

Instead of

 with Button1 do begin
   Left:=10;
   Top:=10;
   Width:=100;
   Height:=25;
 end;

Use

 with Button1 do begin
   SetBounds(10,10,100,25);
 end;

Left, Top, Width, Height are calling SetBounds. And every change of position or size invokes recalculation of all sibling controls and maybe recursively the parent and/or the grandchild controls.

DisableAlign / EnableAlign

When positioning many controls, it is a good idea to disable the recalculation of all auto sizing, aligning, anchoring.

 DisableAlign;
 try
   ListBox1.Width:=ClientWidth div 3;
   ListBox2.Width:=ClientWidth div 3;
   ListBox3.Width:=ClientWidth div 3;
 finally
   EnableAlign;
 end;

Note: Every DisableAlign call needs a EnableAlign call. For example if you call two times DisableAlign, you must call two times EnableAlign.

For Delphians: This works recursively. That means DisableAlign stops aligning in all childs and grand childs.