CashDrawer Implementation
2/27/2008
Most point-of-sale applications will use a cash drawer for financial transactions. Service Object developers can use the POS for .NET class, CashDrawerBase, to easily implement a UPOS-compliant CashDrawer Service Object.
Capabilities
All CashDrawer Service Objects must support, at a minimum, the ability to open the drawer. This is done by implementing the abstract method, CashDrawerBase.OpenDrawerImpl, in your Service Object class.
The Service Object may also be able to determine if the cash drawer is open or not. If the Service Object does have this capability, it should set the CapStatus property to true. If CapStatus is true, then applications may examine the state of the device using the DrawerOpened property. If CapStatus is not set, then DrawerOpened will always be set to false and any attempt to set it to true will generate an exception.
If CapStatus has been set to true, the Service Object needs to update the DrawerOpened property. You should do this in the Service Object's implementation of the OpenDrawerImpl method. A background thread monitoring the state of the device may also set the DrawerOpened property.
CashDrawer Events
If the Service Object has set the CapStatus property to true, CashDrawerBasic.DrawerOpened sends a StatusUpdateEvent to the application.
Depending on the cash drawer device and the Service Object implementation, the Service Object may need a separate thread to monitor the state of the hardware and report any changes asynchronously. This would be necessary, for example, if the cash drawer could be opened manually by the operator and the application needs to be notified.
The CashDrawer Service Object may also send a DirectIOEvent to the application. The DirectIOEvent is used to send data to the application that is specific to the Service Object implementation and may therefore be incompatible with some applications. For more information, see Device Input and Events.
Device Sharing
A cash drawer is a shareable device. Multiple applications will be able to open, enable, and access all of its properties and methods. However, once an application has claimed the device, only that application may call CashDrawerBase.OpenDrawer or CashDrawerBase.WaitForDrawerClose. A PosException with ErrorCode.Claimed will be thrown if other applications attempt to call these methods.
If more than one application has opened and enabled the device, then each application will receive all events sent by the Service Object.
The code necessary to support this feature is implemented in the POS for .NET CashDrawerBase class.
Multiple Cash Drawers
It is possible to have more than one cash drawer attached to the computer and using the same hardware port. In such situations, a CashDrawer Service Object may know to which cash drawer it is not specifically connected. If the Service Object can distinguish to which cash drawer device it is connected, it should set the CapStatusMultiDrawerDetect property to true. The value of this property will influence the behavior of the DrawerOpened property and the WaitForDrawerClose method.
If CapStatusMultiDrawerDetect is set to false, then a DrawerOpened value of true indicates that at least one drawer is open. The application is not able to determine whether any drawer in particular is open.
If CapStatusMultiDrawerDetect is set to false, the method WaitForDrawerClose waits for all open cash drawers to be closed before returning to the application.