PRB: Dynamic Creation of Redistributable Control Fails
ID: Q151804
|
The information in this article applies to:
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Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2, 5.0, 6.0
SYMPTOMS
Attempting to dynamically create an instance of one of the redistributable
ActiveX controls supplied with Visual C++ fails on machines where Visual
C++ has not been installed. However, creating an instance of the same
control on a dialog box succeeds.
CAUSE
The redistributable controls supplied with Visual C++ are licensed.
RESOLUTION
Specify a valid License string when dynamically creating the control.
STATUS
This behavior is by design.
MORE INFORMATION
When Visual C++ is installed on a machine, the entire machine becomes
licensed to use the redistributable ActiveX controls as part of the
installation process. If an instance of one of the redistributable controls
is created dynamically and no License key is specified, the creation will
succeed because the control is able to determine that the entire machine is
licensed and so will allow itself to be created. However, if the same code
that performs the dynamic creation of the control is executed on a machine
that has not had Visual C++ installed on it (such as Visual Basic or
another application that provides the same control), the creation will
fail. In this case the control will not allow itself to be created if a
License key is not specified and the machine has not been licensed.
The CWnd::CreateControl method can be used to dynamically create an
instance of an ActiveX control. When an ActiveX control is inserted into a
Visual C++ project via the Component Gallery, a wrapper class is created
that can be used to work with the control. The wrapper class provides two
overridden versions of the Create method. One of the versions allows a
string to be passed that will be used as the License key when creating the
control; the other version does not.
Dynamic creation of one of the redistributable ActiveX controls will fail
on a machine that has not had Visual C++ installed on it if any of the
following methods are used to create the control:
- The version of the Create method in the wrapper class that does not
allow a License key to be specified is used.
- A NULL string is passed to the Create method in the wrapper class
that does accept a License key.
- The CWnd::CreateControl method is called with a value of NULL for the
License key string.
- IClassFactory::CreateInstanceLic is used with a NULL value as the
License key parameter.
Creating instances of the redistributable ActiveX controls via a dialog box
template will succeed on a machine that has not had Visual C++ installed.
This behavior occurs because the Visual C++ resource editor asks the
control for its License key when the dialog template is created. The
License key is then cached as a DLGINIT resource in the project's .RC file.
At run time, when the MFC dialog box code creates the dialog and its
contained controls, the License key is read from the dialog resource and
used in the call to IClassFactory2::CreateInstanceLic to create the
control.
To allow a licensed control to be dynamically created on a machine that is
not licensed requires passing a License key. An application that performs
dynamic creation of a control must have the control's License key cached in
its own code. This must be done while the application is being designed.
For sample code illustrating how to request a License key from an object,
refer to the following article in the Microsoft Knowledge Base:
Q151771
SAMPLE: LicReqst Shows Requesting a License Key from an Object
The following redistributable controls supplied with Visual C++ 6.0 are licensed and require a license key to be dynamically created on machines
that have not had Visual C++ installed:
| Control File |
Description |
|---|
| anibtn32.ocx |
Animated button Control |
| keysta32.ocx |
Key Status Control |
| mci32.ocx |
Multimedia MCI Control |
| mscomm32.ocx |
Communications Control |
| msflxgrd.ocx |
Flex Grid Control |
| msmask32.ocx |
Masked Edit |
| grid32.ocx |
Grid Control |
| picclp32.ocx |
Picture Clip Control |
| tabctl32.ocx |
Tab Control |
REFERENCES
For more information, please see:
The Visual C++ documentation on the CWnd::CreateControl method.
The Visual C++ documentation on licensing an OLE control.
The Visual C++ documentation on using controls in a non-dialog container.
The OLE Programmer's Reference documentation on the IClassFactory2
interface.
Additional query words:
ocx cdk
Keywords : kbole kbMFC kbVC400 kbVC410 kbVC420 kbVC500
Version : winnt:4.0,4.1,4.2,5.0,6.0
Platform : winnt
Issue type : kbprb