c# - 无法将字符串转换为 int。错误消息 : Input string was not in a correct format

Question

我有以下输出数字“40”的代码:

Hashtable ht = new Hashtable();
ht.Add("numRooms", pageData.Property["romtotalt"].ToString());
string str = ht["numRooms"].ToString();
lblMigrate.Text = i.ToString();

然后我尝试将字符串转换为 int，但出现异常/错误:

Hashtable ht = new Hashtable();
ht.Add("numRooms", pageData.Property["romtotalt"].ToString());
string str = ht["numRooms"].ToString();
int i = Convert.ToInt32(str);  // <-- This is where it fails I t hink. But why??
lblMigrate.Text = i.ToString();

这是我收到的错误信息:

Server Error in '/' Application.
Input string was not in a correct format.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: Input string was not in a correct format.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[FormatException: Input string was not in a correct format.]
   System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal) +7469351
   System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info) +119
   development.templates.HotellGuide.btnMigrateHotels_Click(Object sender, EventArgs e) +956
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565


Version Information: Microsoft .NET Framework Version:2.0.50727.3082; ASP.NET Version:2.0.50727.3082 

我不明白这是怎么回事。我之前多次将 string 转换为 int，从来没有出现过这个问题。

请帮忙:)

更新

我找到了解决办法。我不知道为什么这行得通……但它行得通……
我将转换放在 Try Catch 中，现在它可以工作了。图一:op

int numRooms = 0;
int numAllergyRooms = 0;

try
{
    numRooms = Convert.ToInt32(newHotel["numRooms"].ToString().Trim());
    numAllergyRooms = Convert.ToInt32(newHotel["numAllergyRooms"].ToString().Trim());
}
catch (Exception ex)
{
    Console.WriteLine("{0} Exception caught.", ex);
}

Answer 1

我认为“输入字符串的格式不正确”这一行说明了一切。在行中

 int i = Convert.ToInt32(str);

str 可能包含字母字符。边调试边看，里面有什么？