Overwrite wincontrol property only if needed

[PizzaProgram 9]

Probably this is a very basic question, but I simply can not find any working method...

 

I'd like to change properties of many wincontrols, but only if necessary.

Reason: I'm using special skinned components (AlphaSkin) and they call unnecessary repaint events.

 

The trivial "solution" is to write code 2x:

if myForm.Left <> calculateMySpecialValue(...) then
    myForm.Left := calculateMySpecialValue(...);

But I'd like to have a universal procedure I can apply to everything! (TFont.Size, Grid1.Column.Width , etc.)

 

I've tried this:

procedure WR( i: PInteger; const new: integer );
begin
    if i^ <> new then
       i^ := new;
end;

 

But it does not compile with Delphi7 on many places.

WR( @grid1.Columns[i].Width, trunc(grid1.Columns[i].Width * scale)-1); // ERROR: Variable required
WR( PInteger(Addr(grid1.TitleFont.Size)), rFmv);                       // ERROR: Variable required

 

[Remy Lebeau 1260]

You can't take a pointer to a property, like you are trying to do.  You should look into using RTTI instead.  Someone else was asking a similar question on StackOverflow just yesterday:

 

https://stackoverflow.com/questions/76729720/how-do-i-get-a-pointer-to-a-property-in-delphi

[PizzaProgram 9]

OK, so it's not so simple, as I've hoped 😞

 

If I understand it right, I will need :

GetPropValue() and SetPropValue() functions

 

or rather: GetInt64Prop() ?

interesting is I could not find any GetInt32Prop() nor GetIntProp() ...

 

.. and I will need to call it somehow with :
 

WR( o: object; const name: string; const v: integer )
WR( grid1.columns[i], 'Width', 66 );

 

right ?

 

[KodeZwerg 54]

I can not answer if it is implemented in your Delphi 7 installation, maybe upgrade to a more common Delphi Community Edition can help.

uses
  ...TypInfo, Rtti...


function SetProperty(const AControl: TControl; const AProperty: string; const AValue: TValue): Boolean;
var
  LControl: TControl;
  LRttiContext: TRttiContext;
  LRttiProperty: TRttiProperty;
begin
  Result := False;
  try
    LControl := AControl;
    LRttiProperty := LRttiContext.GetType(LControl.ClassType).GetProperty(AProperty);
    if ((LRttiProperty <> nil) and (LRttiProperty.Visibility in [mvPrivate, mvProtected, mvPublic, mvPublished])) then
    begin
      LRttiProperty.SetValue(LControl, AValue);
      Result := True;
    end;
  except
  end;
end;

Call that method by giving a control as argument 1, write the property as it is named for argument 2 and finally as argument 3 put your wanted value in.
Best of luck.

[Remy Lebeau 1260]

2 hours ago, PizzaProgram said:

If I understand it right, I will need :

GetPropValue() and SetPropValue() functions

I tend to stay away from those functions since they use Variant, which is usually unnecessary overhead.  But it depends on your particular needs.

2 hours ago, PizzaProgram said:

or rather: GetInt64Prop() ?

interesting is I could not find any GetInt32Prop() nor GetIntProp() ...

Integral properties are handled by GetOrdProp() and SetOrdProp() (as in, Ordinal)

[Remy Lebeau 1260]

1 hour ago, KodeZwerg said:

I can not answer if it is implemented in your Delphi 7 installation

Extended RTTI via the System.Rtti unit was introduced in Delphi 2010.

1 hour ago, KodeZwerg said:

if ((LRttiProperty <> nil) and (LRttiProperty.Visibility in [mvPrivate, mvProtected, mvPublic, mvPublished])) then 

 

Why filter by visibility rather than by writability?

if (LRttiProperty <> nil) and LRttiProperty.IsWritable then 

 

Edited July 22, 2023 by Remy Lebeau

[Brian Evans 83]

Could try overloads of a procedure. From the calling site it does what you want but requires a separate definition for each combination of argument types / number of arguments. 

 

Procedures and Functions - Overloading (Delphi) - RAD Studio (embarcadero.com)

 

Added: Looks like not much use here due to not being able to easily get a reference to the property as a property vs as a value.

Edited July 22, 2023 by Brian Evans