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

Creating Containers

LEAD provides specific functions for creating each type of container:

• L_TwainCreateNumericContainerArray, allocates the container of the TW_CAPABILITY structure to be of type TW_ARRAY and fills it with the specified data.
• L_TwainCreateNumericContainerEnum, allocates the container of the TW_CAPABILITY structure to be of type TW_ENUMERATION and fills it with the specified data.
• L_TwainCreateNumericContainerOneValue, allocates the container of the TW_CAPABILITY structure to be of type TW_ONEVALUE and fills it with the specified data.
• L_TwainCreateNumericContainerRange, 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 L_TwainLockContainer, make the desired changes to the container value(s), and then call L_TwainUnlockContainer. Alternately, the user can accomplish the same thing by calling the C API GlobalLock and GlobalUnlock functions.

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

Getting Container Values

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 L_TwainGetNumericContainerItemType. After the type is known, the following functions can be used to get the container value(s) from the TW_CAPABILITY structure:

• L_TwainGetNumericContainerINTValue
• L_TwainGetNumericContainerUINTValue
• L_TwainGetNumericContainerFIX32Value
• L_TwainGetNumericContainerFRAMEValue
• L_TwainGetNumericContainerSTRINGValue
• L_TwainGetNumericContainerUNICODEValue
• L_TwainGetNumericContainerBOOLValue

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

For more information on these container types, refer to the TWAIN specification.