Exception Classes

2/27/2008

POS for .NET error handling is implemented through the use of exceptions. The four POS for .NET exception classes are as follows:

• PosException
• PosControlException
• PosManagementException
• PosLibraryException

Standard UPOS error codes are represented by the ErrorCode enumeration.

PosException

PosException is the Base exception class for PosControlException, PosManagementException, and PosLibraryException. PosException is derived from System.Exception.

PosControlException

PosControlException is the standard exception thrown by Service Objects to POS for .NET applications.

PosManagementException

PosManagementException is thrown by POS for .NET Device Management. Applications and Service Objects must not throw PosManagementException.

PosLibraryException

PosLibraryException is thrown by PosExplorer. Applications and Service Objects must not throw PosLibraryException.

Error Codes

The following table provides a mapping between the UPOS standard error codes and the ErrorCode values that POS for .NET provides.

Example

The following code example demonstrates how MSR handles POS exceptions and uses the ErrorCodes contained in those exceptions to gather information about them.

// Create a new instance of the MSR and opens the device.
msr = (Msr)explorer.CreateInstance(msrinfo);
msr.Open();

// Try to enable the device without first claiming it. 
// This will throw a PosControlException which, through 
// its ErrorCode, will yield information about the exception.
try
{
   msr.DeviceEnabled = true;
}
catch (PosControlException e)
{ 

   // Examine the ErrorCode to determine the cause of the error.
   if (e.ErrorCode == ErrorCode.NoHardware)
   { 
      Console.WriteLine("The POS device is not connected ");
      Console.WriteLine("to the system or is not turned on.");
   }
   if (e.ErrorCode == ErrorCode.Timeout)
   {
      Console.WriteLine("The Service Object timed out 
            waiting for a response from the POS device.");
   }
   
   // The example has not claimed the MSR, which is an 
   // exclusive-access device, before trying to enable 
   // it. This will throw the PosControlException 
   // and trigger the following conditional block. 
   // Once triggered, the MSR will be claimed and enabled.
   if (e.ErrorCode == ErrorCode.NotClaimed)
   {
      Console.WriteLine("The POS application attempted to access ");
      Console.WriteLine("an exclusive-use device that must be ");
      Console.WriteLine("claimed before the method or property ");
      Console.WriteLine("set action can be used.")
      msr.Claim(1000); 
      msr.DeviceEnabled = true;
   }   
}

See Also

Reference

PosException
PosControlException
PosManagementException
PosLibraryException

Concepts

PosExplorer Class
POS Exception Handling

Other Resources

POS for .NET API Support