What is hWnd & hDC

[mleach2]

What is hWnd & hDC and what do I need them for? I have an activex control that uses them in a sub.

Sub DrawtoPictureBox(hWnd as long, hDC as long)



Thanks for the help
ML

[kleinma]

well hWnd is the windows handle of an object.. here is a little excerpt from MSDN

How Windows Works: Windows, Events and Messages
A complete discussion of the inner workings of Windows would require an entire book. A deep understanding of all of the technical details isn't necessary. A simplified version of the workings of Windows involves three key concepts: windows, events and messages.

Think of a window as simply a rectangular region with its own boundaries. You are probably already aware of several different types of windows: an Explorer window in Windows, a document window within your word processing program, or a dialog box that pops up to remind you of an appointment. While these are the most common examples, there are actually many other types of windows. A command button is a window. Icons, text boxes, option buttons and menu bars are all windows.

The Microsoft Windows operating system manages all of these many windows by assigning each one a unique id number (window handle or hWnd). The system continually monitors each of these windows for signs of activity or events. Events can occur through user actions such as a mouse click or a key press, through programmatic control, or even as a result of another window's actions.

Each time an event occurs, it causes a message to be sent to the operating system. The system processes the message and broadcasts it to the other windows. Each window can then take the appropriate action based on its own instructions for dealing with that particular message (for example, repainting itself when it has been uncovered by another window).

As you might imagine, dealing with all of the possible combinations of windows, events and messages could be mind-boggling. Fortunately, Visual Basic insulates you from having to deal with all of the low-level message handling. Many of the messages are handled automatically by Visual Basic; others are exposed as Event procedures for your convenience. This allows you to quickly create powerful applications without having to deal with unnecessary details.

[kleinma]

and here is hDC

Returns a handle provided by the Microsoft Windows operating environment to the device context of an object.

Syntax

object.hDC

The object placeholder represents an object expression that evaluates to an object in the Applies To list.

Remarks

This property is a Windows operating environment device context handle. The Windows operating environment manages the system display by assigning a device context for the Printer object and for each form and PictureBox control in your application. You can use the hDC property to refer to the handle for an object's device context. This provides a value to pass to Windows API calls.

With a CommonDialog control, this property returns a device context for the printer selected in the Print dialog box when the cdlReturnDC flag is set or an information context when the cdlReturnIC flag is set.

Note The value of the hDC property can change while a program is running, so don't store the value in a variable; instead, use the hDC property each time you need it.

The AutoRedraw property can cause the hDC property setting to change. If AutoRedraw is set to True for a form or PictureBox container, hDC acts as a handle to the device context of the persistent graphic (equivalent to the Image property). When AutoRedraw is False, hDC is the actual hDC value of the Form window or the PictureBox container. The hDC property setting may change while the program is running regardless of the AutoRedraw setting.

If the HasDC property is set to False, a new device context will be created by the system and the value of the hDC property will change each time it is called.

[axion_sa]

the hWnd (Window Handle) is a unique ID given to every control/window etc.
the hDC (Device Context) is a reference used in painting onto a control. (I am open to correction to this one)

[MerrionComputin]

See this VB class for all sorts of things you can do with device contexts....