Question

VS 异常详细信息: System.ArgumentNullException: 值不能为 null。参数名: String

using System;

public partial class Finish : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
this.Title = "结账";
if (Session["buy"] == null)
{
Response.Redirect("Default.aspx");
}
else
{
string strBookName = Session["buy"].ToString();
strBookName = strBookName.Remove(strBookName.Length -1, 1);
string strNum = Request.QueryString["num"];
Response.Write("<b>你选购的 " + strNum + " 本图书有：<br><br></b>" + strBookName + "<br><br>");
float fCost = 15 * int.Parse(strNum);
Response.Write("本站所有图书单价均为15元，你应付" + fCost.ToString() + "元");
}
}
}
[FormatException: 输入字符串的格式不正确。]
System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) +12738969
System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) +120
System.Int32.Parse(String s) +24
Finish.Page_Load(Object sender, EventArgs e) in e:\Users\17556\Desktop\asp第三次作业\Finish.aspx.cs:18
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +51
System.Web.UI.Control.OnLoad(EventArgs e) +95
System.Web.UI.Control.LoadRecursive() +59
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +678
这要怎么解决？

Answer 1

ArgumentNullException 当将空引用（在 Visual Basic 中为 Nothing）传递给不接受它作为有效参数的方法时引发的异常，而NullReferenceException是尝试空对象引用时引发的异常。可以参考msdn的详细说明