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Changing component class at run-time on demand

This is easier as thought (thanks to Hallvard’s Blog – Hack#14: Changing the class of an object at run-time): procedure PatchInstanceClass(Instance: TObject; NewClass: TClass); type PClass = ^TClass; begin if Assigned(Instance) and Assigned(NewClass) and NewClass.InheritsFrom(Instance.ClassType) and (NewClass.InstanceSize = Instance.InstanceSize) then begin PClass(Instance)^ := NewClass; end; end; type TMyButton = class(TButton) public procedure Click; override; end; … Read more

DecimalSeparator in SysUtils and System.SysUtils

My bad, first I needed to call FormatSettings, and then I can use in DecimalSeparator in Delphi XE6, FormatSettings.DecimalSeparator

How to detach a panel and show it in a separate window?

As noted by others, there are several problems with changing the parent window of a control without changing the ownership, and changing a controls owner can be difficult if it has multiple controls sitting on it… One way around it is to use a frame instead. A frame owns all of it’s sub-controls, so all … Read more

Delphi Change main form while application is running

Is it possible to change the main form while the application is already running? It is not possible to change the VCL main form whilst the program is running. This property is determined once and for all when the program starts. One possible way to proceed for you is to arrange for the secondary form, … Read more

How to avoid issues when embedding a TForm in another TForm?

I do this as well and I use the following routine to make it happen: procedure TMyForm.PlaceInsideContainer(Container: TWinControl); begin Parent := Container; Align := alClient; BorderIcons := []; BorderStyle := bsNone; ParentBackground := True; Show; end; I have no problems with this. The only difference that I could possibly imagine could be relevant is the … Read more

Load Jpg/Gif/Bitmap and convert to Bitmap

Delphi 2009 comes with built in support for JPEG, BMP, GIF and PNG. For earlier versions of Delphi you may need to find third party implementations for PNG and GIF, but in Delphi 2009 you simply add the Jpeg, pngimage and GIFImg units to your uses clause. If the file has an extension you can … Read more

How to add mouse wheel support to a component descended from TGraphicControl?

Due to several VCL constructs (whether they are deliberate implementation choices or may possibly be bugs1), I leave in the middle) only the focused control and all its parents get mouse wheel messages, as well as the control which has the mouse captured ánd has a focused parent. At the TControl level, the latter condition … Read more