B4X Requires Chilkat v11.7.0+

QR Code Error Correction Levels

See more QR Code Examples

Demonstrates the four QR error-correction levels. L, M, Q and H allow a reader to recover the data when about 7%, 15%, 25% and 30% of the symbol is damaged or covered. More error correction leaves less room for data, so the same text needs a larger symbol at a higher level. The default is M. The example also shows boostErrorCorrection, which raises the level for free when the chosen version has room to spare. B4X

Dim success As Boolean = False

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

Dim fmt As ChilkatFormats
fmt.Initialize
Dim json As ChilkatJsonObject
json.Initialize
Dim jsonOut As ChilkatJsonObject
jsonOut.Initialize
json.UpdateString("payload.text", "https://www.chilkatsoft.com/barcode_overview.asp")

'  Encode the same text at each level.
Dim levels As ChilkatJsonArray
levels.Initialize
levels.Load("[" & Chr(34) & "L" & Chr(34) & "," & Chr(34) & "M" & Chr(34) & "," & Chr(34) & "Q" & Chr(34) & "," & Chr(34) & "H" & Chr(34) & "]")
Dim i As Int
For i = 0 To 3
    json.UpdateString("encoding.qr.errorCorrection", levels.StringAt(i))
    success = fmt.QrCode("generate", json, jsonOut)
    If success = False Then
        Log(fmt.LastErrorText)
        Return
    End If

    Log("level " & levels.StringAt(i) & ": version " & jsonOut.IntOf("symbols[0].selectedEncoding.version") & ", " & jsonOut.IntOf("symbols[0].dimensions.modulesWide") & " modules wide")
Next

'  The four symbols.  They hold the same text, and the higher the level, the larger the symbol:

'  

'  A symbol often has room left over.  boostErrorCorrection uses it: the level is raised
'  as far as the same version allows, so the symbol is no larger but is more robust.
Dim json2 As ChilkatJsonObject
json2.Initialize
json2.UpdateString("payload.text", "https://chilkatsoft.com")
json2.UpdateString("encoding.qr.errorCorrection", "L")
success = fmt.QrCode("generate", json2, jsonOut)
If success = False Then
    Log(fmt.LastErrorText)
    Return
End If

Log("level L requested: version " & jsonOut.IntOf("symbols[0].selectedEncoding.version") & ", level " & jsonOut.StringOf("symbols[0].selectedEncoding.errorCorrection"))

json2.UpdateBool("encoding.qr.boostErrorCorrection", True)
success = fmt.QrCode("generate", json2, jsonOut)
If success = False Then
    Log(fmt.LastErrorText)
    Return
End If

Log("level L with boost: version " & jsonOut.IntOf("symbols[0].selectedEncoding.version") & ", level " & jsonOut.StringOf("symbols[0].selectedEncoding.errorCorrection"))

'  Level L, and level M reached by the boost.  The two symbols are the same size:

'  

'  Sample output:

'  level L: version 3, 29 modules wide
'  level M: version 4, 33 modules wide
'  level Q: version 5, 37 modules wide
'  level H: version 6, 41 modules wide
'  level L requested: version 2, level L
'  level L with boost: version 2, level M