How to Work with the Containers

When getting or setting capability information, it may be necessary to create a container for the associated TW_CAPABILITY structure. The structure of these containers depends on the type of information in the container. LEADTOOLS supports the following types of containers:

TW_ARRAY

TW_ENUMERATION

TW_ONEVALUE

TW_RANGE

For more information on these container types, refer to the TWAIN 1.9 Specification, available at www.twain.org.

For each type of container, LEAD provides a specific function:

LTwain::CreateNumericContainerArray, allocates the container of the TW_CAPABILITY structure to be of type TW_ARRAY and fills it with the specified data.

LTwain::CreateNumericContainerEnum, allocates the container of the TW_CAPABILITY structure to be of type TW_ENUMERATION and fills it with the specified data.

LTwain::CreateNumericContainerOneValue, allocates the container of the TW_CAPABILITY structure to be of type TW_ONEVALUE and fills it with the specified data.

LTwain::CreateNumericContainerRange, allocates the container of the TW_CAPABILITY structure to be of type TW_RANGE and fills it with the specified data.

The value in a container can be changed once the user has a pointer to the container. To change the value of a container, the user can call LTwain::LockContainer, make the desired changes to the container value(s), and then call LTwain::UnlockContainer. Alternately, the user can accomplish the same thing be calling the API GlobalLock and GlobalUnlock functions.

When the created container is no longer needed, it should be freed by calling LTwain::FreeContainer.

LEAD provides a number of functions for getting container values, based on the data type of the value. To get the data type of the value in a container, call LTwain::GetNumericContainerItemType. Once the type is known, the following functions can be used to get the container value(s) from the TW_CAPABILITY structure:

LTwain::GetNumericContainerINTValue

LTwain::GetNumericContainerUINTValue

LTwain::GetNumericContainerFIX32Value

LTwain::GetNumericContainerFRAMEValue

LTwain::GetNumericContainerSTRINGValue

LTwain::GetNumericContainerUNICODEValue

LTwain::GetNumericContainerBOOLValue

To get the available values for a specific TWAIN capability, call LTwain::QueryProperty. This function takes a pointer to a LTWAINPROPERTYQUERY structure, which will be updated with the available values for the capability.