在线急等！未将对象的引用设置到对象的实例！

[jingsijingyu]

代码如下：
protected void Page_Load(object sender, EventArgs e)
{
string productID = Request.QueryString["ProductID"].ToString();//这一行一直报错，可是不知道怎样改正
string photoSize = Request.QueryString["Size"].ToString();
System.Data.SqlClient.SqlDataReader imageReader;
string dbConn = ConfigurationManager.ConnectionStrings["MyAdventureWorksConnectionString1"].ConnectionString;
System.Data.SqlClient.SqlConnection sqlConn = new System.Data.SqlClient.SqlConnection(dbConn);
sqlConn.Open();
System.Data.SqlClient.SqlCommand imageCommand = new System.Data.SqlClient.SqlCommand(
"SELECT ThumbNailPhoto, LargePhoto FROM Product "
+ "INNER JOIN ProductProductPhoto ON Product.ProductID = ProductProductPhoto.ProductID "
+ "INNER JOIN ProductPhoto ON ProductProductPhoto.ProductPhotoID = ProductPhoto.ProductPhotoID "
+ "WHERE Product.ProductID=" + productID,sqlConn);
imageReader = imageCommand.ExecuteReader(CommandBehavior.CloseConnection);
try
{
imageReader.Read();
if (photoSize == "ThumbNail")
{
byte[] imageBytes = (byte[])imageReader["ThumbNailPhoto"];
Response.ContentType = "image/GIF";
Response.BinaryWrite(imageBytes);
}
else if (photoSize == "Large")
{
byte[] imageBytes = (byte[])imageReader["LargePhoto"];
Response.ContentType = "image/JPEG";
Response.BinaryWrite(imageBytes);
}
}
finally
{
imageReader.Close();
sqlConn.Close();
}

}

发生的错误是：
未将对象引用设置到对象的实例。
错误行： string productID = Request.QueryString["ProductID"].ToString();


请高手指教！

[hahanan1987]

首先这个Request.QueryString["ProductID"]返回的就是字符串
再者你可以加个判断 string.isNullOrEmpty(Request.QueryString["ProductID"])

[孟子E章]

if(Request.QueryString["ProductID"]!=null)
productID = Request.QueryString["ProductID"].ToString();
else
productID = "0";

[孟子E章]

url里面没有 ProductID=xxx 这样的参数

[generhappy]

string productID = Request.QueryString["ProductID"].ToString();//

如果传过来的ProductID 为空值，自然会报错，首先if他为非空吧，顶楼上！

[龍月]

[Quote=引用 2 楼 net_lover 的回复:]
if(Request.QueryString["ProductID"]!=null)
productID = Request.QueryString["ProductID"].ToString();
else
productID = "0";
[/Quote]
+5

[porschev]

做参数的非空判断。。再对它进行操作