我在“异常”部分遇到错误，我不知道为什么

Question

当我运行这段代码时，我在 catch（异常 e）部分出现错误，我不知道为什么，编译器说“不能在此范围内声明名为 'e' 的局部变量，因为它会给 ' 赋予不同的含义e'，它已经在“父级或当前”范围中使用来表示其他内容”

        try
        {

            //Form Query which will insert Company and will output generated id 
            myCommand.CommandText = "Insert into Comp(company_name) Output Inserted.ID VALUES (@company_name)";
            myCommand.Parameters.AddWithValue("@company_name", txtCompName);
            int companyId = Convert.ToInt32(myCommand.ExecuteScalar());

            //For the next scenario, in case you need to execute another command do it before committing the transaction

            myTrans.Commit();

            //Output Message in message box
            MessageBox.Show("Added", "Company Added with id" + companyId, MessageBoxButtons.OK, MessageBoxIcon.Information);

        }

        catch (Exception e)
        {
            try
            {
                myTrans.Rollback();
            }
            catch (SqlException ex)
            {
                if (myTrans.Connection != null)
                {
                    MessageBox.Show("An exception of type " + ex.GetType() +
                                      " was encountered while attempting to roll back the transaction.");
                }
            }

            MessageBox.Show("An exception of type " + e.GetType() +
                              "was encountered while inserting the data.");
            MessageBox.Show("Record was written to database.");

        }
        finally
        {
            myConnection.Close();
        }

希望您的回复！谢谢！

Answer 1

您有一个e在本地范围内其他地方命名的变量，并且无法消除两者之间的歧义。

您很可能处于带有指定EventArgs参数的事件处理程序中e，并且您应该将其中一个e标识符重命名为其他名称。

以下示例说明了此问题：

1. 参数名称冲突

   void MyEventHandler(object source, EventArgs e)
   //                                          ^^^
   {
       try
       {
           DoSomething();
       }
       catch (Exception e)
       //              ^^^
       {
           OhNo(e);
           // Which "e" is this? Is it the Exception or the EventArgs??
       }
   }
   

2. 冲突的局部变量

   void MyMethod()
   {
       decimal e = 2.71828;
       //     ^^^
   
       try
       {
           DoSomething();
       }
       catch (Exception e)
       //              ^^^
       {
           OhNo(e);
           // Which "e" is this? Is it the Exception or the Decimal??
       }
   }
   

3. 匿名函数（lambda）

   void MyMethod()
   {
       decimal e = 2.71828;
       //     ^^^
   
       var sum = Enumerable.Range(1, 10)
                           .Sum(e => e * e); //Which "e" to multiply?
       //                      ^^^
   }
   

请注意，以下内容不会导致相同的错误，因为您可以使用关键字消除this歧义：

class MyClass
{
    int e;

    void MyMethod()
    {
        try
        {
            DoSomething(e); //Here it is the Int32 field
        }
        catch (Exception e)
        {
            OhNo(e); //Here it is the exception
            DoSomethingElse(this.e); //Here it is the Int32 field
        }
    }

}