Data Decoding (POS for .NET v1.14 SDK Documentation)
The ScannerBase class provides two methods, DecodeDataLabel and DecodeScanDataType for decoding incoming date. These methods are called when the properties ScanDataLabel and ScanDataType, respectively, are accessed. The ScannerBase class defers data decoding until the application accesses the data properties and the decoded data will be cached for future reads.
The ScannerBase class implements the ScannerBase.DecodeData attribute as required by the Unified Point Of Service (UnifiedPOS) specification. If DecodeData is not set to true when the application reads the ScanDataLabel property, an empty byte array will be returned. Similarly, ScanDataType returns BarCodeSymbology.Unknown. This functionality is implemented in the ScannerBase class and is transparent to both the application and the Service Object.
To implement DecodeScanDataLabel
Override the protected, virtual ScannerBasic member DecodeScanDataLabel.
DecodeScanData takes an argument, scanData, which contains the complete data buffer. There is no need to cache any additional data in the Service Object code.
DecodeScanData should process the scanned data to remove header and type information at the start and end of the data buffer. The modified buffer will be returned in a byte array.
To implement DecodeScanDataType
Override the protected, virtual ScannerBasic member DecodeScanDataType.
Like DecodeScanDataLabel, DecodeScanDataType receives an argument containing the complete scanned buffer.
DecodeScanDataType examines the buffer to find the data type of the scanned data and returns the appropriate BarCodeSymbology value.
Example
The following code demonstrates a typical method the Service Object developer could implement in order to extract label and data values from a scanned buffer. Note that this code is demonstrative of a particular device. Different Service Objects will require device-specific decoding.
// Decode the incoming scanner data, removing header and
// type information.
override protected byte[] DecodeScanDataLabel(
byte[] scanData)
{
int i;
int len = 0;
// Get length of label data.
for (i = 5; i < (int)scanData[1]
&& (int)scanData[i] > 31; i++)
{
len++;
}
// Copy label data into buffer.
byte[] label = new byte[len];
len = 0;
for (i = 5; i < (int)scanData[1]
&& (int)scanData[i] > 31; i++)
{
label[len++] = scanData[i];
}
return label;
}
// Process the incoming scanner data to find the data type.
override protected BarCodeSymbology DecodeScanDataType(
byte[] scanData)
{
int i;
for (i = 5; i < (int)scanData[1]
&& (int)scanData[i] > 31; i++)
{
}
// last 3 (or 1) bytes indicate symbology.
if (i + 2 <= (int)ScanData[1])
{
return GetSymbology(
ScanData[i],
ScanData[i + 1],
ScanData[i + 2]);
}
else
{
return GetSymbology(ScanData[i], 0, 0);
}
}
// This method determines the data type by examining
// the end of the scanned data buffer. Either 1 byte
// or 3 byte is used to determine the type, depending on
// the incoming buffer.
static private BarCodeSymbology GetSymbology(
byte b1,
byte b2,
byte b3)
{
if (b1 == 0 && b3 == 11)
{
// Use all 3 bytes to determine the date type.
switch (b2)
{
case 10:
return BarCodeSymbology.Code39;
case 13:
return BarCodeSymbology.Itf;
case 14:
return BarCodeSymbology.Codabar;
case 24:
return BarCodeSymbology.Code128;
case 25:
return BarCodeSymbology.Code93;
case 37:
return BarCodeSymbology.Ean128;
case 255:
return BarCodeSymbology.Rss14;
default:
break;
}
}
else if (b2 == 0 && b3 == 0)
{
// Only use the first byte to determine the data type.
switch (b1)
{
case 13:
return BarCodeSymbology.Upca;
case 22:
return BarCodeSymbology.EanJan13;
case 12:
return BarCodeSymbology.EanJan8;
default:
break;
}
}
return BarCodeSymbology.Other;
}
Additional details about how label and type data should be extracted from a scanned data buffer can be found in the UPOS specification.
Compiling the Code
- For additional information about creating and compiling a Service Object project, see Service Object Samples: Getting Started.
