Values are showing null on button click

Question

Hi,

 

My Code is:

public partial class RoughPage : System.Web.UI.Page
{
byte[] imageSize; public int a;
protected void Page_Load(object sender, EventArgs e)
{
}
public void btnUpload_Click(object sender, EventArgs e)
{
if (ImgUpload.HasFile)
{
a = 8;
imageSize = new byte[ImgUpload.PostedFile.ContentLength];
HttpPostedFile uploadedImage = ImgUpload.PostedFile;
uploadedImage.InputStream.Read(imageSize, 0, (int)ImgUpload.PostedFile.ContentLength);
hfPic.Value = "Y";
}
}
public void btnUpload1_Click(object sender, EventArgs e)
{
int b = a;
byte[] aa = imageSize;
}
}

Plz tell me, why value of 'b' and 'aa' are null on "btnUpload1_Click". how to get value of 'imageSize'

 

Thanks in advance