Tag Archives: windows

Preserve Internal State (/Window Handle) when Changing Parent or Style for an ActiveX Control – aka How To RecreateWnd “Properly” for TOleContainer ancestors

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In any (VCL) Delphi application more stuff happens behind the scenes than you might be aware of.
As known, every (TWinControl descendant) control placed on a form (like TButton or TEdit) and even the (T)Form itself is actually a wrapper for a Windows screen object. Every such object is “defined” by something called Window Handle. You can use the Handle value to do stuff with the underlying Windows screen object like hide or show it or move around its parent (another Windows screen object) or change some of its properties.
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Receive Windows Messages In Your Custom Delphi Class – NonWindowed Control/Object

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Windows messages are a key ingredient in communication between Windows and (your) application and also in communication between (two) applications.

Even without your knowledge Windows messages are being posted and handled by forms in your application.

For example, when the user closes the form in your application, the WM_CLOSE message is sent to the window/form and the form gets closed (if you do not react programmatically).

For an application to receive a Window message, the application must provide a *window* a message will be sent to. In normal situation this window is the (main) form in your application. You write a procedure to handle a specific message, like WM_NCHitTest, and you are done.

BUT, what if you do NOT have a window to receive a message? What if you want to handle messages in your custom class derived from TObject?
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Screen Shuffling with Delphi (first step to a Sliding Puzzle Game)

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I’m sure you’ve seen it already. When the program starts it takes a picture of the current desktop, the picture is then cut into a number of rectangular pieces (all of the same size). A piece at some random position is “removed”. The main code randomly swaps that piece with the one next to it. Only pieces adjacent to the removed one can be moved into it.
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Generic Solution to Coloring the Focused Entry Control in Delphi Applications

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Coloring Focused Entry Control
Looking for the best approach to change the background color (and other properties) of the focused data entry control in a Delphi (VCL) application?

By (Windows) design, the control on a data entry form which has the input focus is not drawn (/highlighted) differently from other controls (i.e. those without the input focus). In case of the TEdit (or TMemo and alike) control, only the blinking insertion point is displayed.

To provide visually more attractive user-friendly interfaces for your Delphi applications, you could decide to change the background color (and maybe some other properties) of the currently selected control – the one that has the input focus. Of course, this would include restoring to the original background color when the focus shifts to another control.
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Delphi High-DPI Road: Ensuring Your UI Looks Correctly for TImage, TColorBox, Owner Drawn TComboBox , TStatusBar and some more

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So you want to go down the high-DPI road? Feeling alone? I did 🙂 The classical answer “it works on my machine” will not be sufficient here. Your non high-dpi aware Delphi application might look nice on your development machine, but it certainly looks super small or ugly stretched on your client’s shiny new 4K resolution laptop – and it really does not work – at least not how you and your client would expect!

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