Encounter Nullpointer error

Question

I am having problem with nullpointer. I cant seem to understand why my code is wrong. Any help will be greatly appreciated. This is my code:

     protected void Page_Load(object sender, EventArgs e)
   {

    Product aProd = new Product(); 
     // Get Product ID from querystring 
     string prodID = Request.QueryString["ProdID"].ToString(); (null pointer occurs at this line. )

    prod = aProd.getProduct(prodID); 
      //Display product details on web form 

     lbl_ProdName.Text = prod.Product_Name;    
    lbl_ProdDesc.Text = prod.Product_Desc;    
    lbl_Price.Text = prod.Unit_Price.ToString("c");
    img_Product.ImageUrl = "~\\Images\\" + prod.Product_Image;    

    //Store the value in invisible fields 
    lbl_Price.Text = prod.Unit_Price.ToString();      
    lbl_ProdID.Text = prodID.ToString(); 
}

These are the code for Product.cs. I still have no idea where my codes went wrong

      public class Product
   {

string _connStr = ConfigurationManager.ConnectionStrings["HealthDBContext"].ConnectionString;
private string _prodID = null;
private string _prodName = string.Empty;
private string _prodDesc = ""; // this is another way to specify empty string
private decimal _unitPrice = 0;
private string _prodImage = "";
private int _stockLevel = 0;

// Default constructor
public Product()
{
}

// Constructor that take in all data required to build a Product object
public Product(string prodID, string prodName, string prodDesc,
               decimal unitPrice, string prodImage, int stockLevel)
{
    _prodID = prodID;
    _prodName = prodName;
    _prodDesc = prodDesc;
    _unitPrice = unitPrice;
    _prodImage = prodImage;
    _stockLevel = stockLevel;
}

// Constructor that take in all except product ID
public Product(string prodName, string prodDesc,
       decimal unitPrice, string prodImage, int stockLevel)
    : this(null, prodName, prodDesc, unitPrice, prodImage, stockLevel)
{
}

// Constructor that take in only Product ID. The other attributes will be set to 0 or empty.
public Product(string prodID)
    : this(prodID, "", "", 0, "", 0)
{
}

// Get/Set the attributes of the Product object.
// Note the attribute name (e.g. Product_ID) is same as the actual database field name.
// This is for ease of referencing.
public string Product_ID
{
    get { return _prodID; }
    set { _prodID = value; }
}
public string Product_Name
{
    get { return _prodName; }
    set { _prodName = value; }
}
public string Product_Desc
{
    get { return _prodDesc; }
    set { _prodDesc = value; }
}
public decimal Unit_Price
{
    get { return _unitPrice; }
    set { _unitPrice = value; }
}
public string Product_Image
{
    get { return _prodImage; }
    set { _prodImage = value; }
}
public int Stock_Level
{
    get { return _stockLevel; }
    set { _stockLevel = value; }
}

As you say, the error occurs when you call `Request.QueryString["ProdID"].ToString()`. Therefore, either `Request`, `Request.QueryString`, or `Request.QueryString["ProdID"]` is `null`. — Martin, Jun 24 '15 at 16:02
Test that Request.QueryString["ProdID"] is not null before trying to call the .ToString() method — Les, Jun 24 '15 at 16:05

jlevet · Answer 1 · 2015-06-25T07:50:00.153

0

Request.QueryString["ProdID"] is returning null. So your ToString() call cause a System.NullPointerException

Solution : ensure that your Request.QueryString["ProdID"] call sends you back the correct object, or test the result yourself:

var obj = Request.QueryString["ProdID"];
string prodID = obj == null ? String.Empty : obj.ToString();

edited Jun 25 '15 at 07:50

answered Jun 24 '15 at 16:11

jlevet

94
8

is there any way to solve the problem ? – Ng Wei Ze Jun 24 '15 at 16:16
@NgWeiZe Of course, i've edited my previous answer. – jlevet Jun 25 '15 at 07:48

Encounter Nullpointer error

1 Answers1