GriauleFingerprintLibrary .FingerprintCore ObjFinger getting Null...! how to set a value

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C#

C#4.0

fingerprint

Hi,


Here is my code

public frmPurchaseMaster(FingerprintCore fp)
       {
            dpStartDate.Text = ClassProductBAL.getCurrentDate().Value.ToShortDateString();
           fingerPrint = fp;
           InitializeComponent();

       }

when i call this i am getting fp null..
where i am wrong..?
I ant to capture finger print scan based on some condition.
how can i...?