datareader 失败但不引发异常 c#

Question

我是 C# 的新手，我发现一些异常处理或缺少异常处理令人费解。我试图捕捉这些异常，但它们没有被捕捉到，我不明白为什么。代码将在异常之后出现，并且异常之后的所有内容都将被忽略，执行的下一行将是表单的绘制事件。

显然，我可以轻松修复此示例，但我想知道为什么没有引发异常。这个我见多了。

这是一个例子：

public DataTable GetTaskDescription( string EstmateNameGuid)
    {
        string strJobNumName = null;

        MySqlCommand cmd = null;
        MySqlDataReader dr = null;
        MySqlConnection myconnection = new MySqlConnection(clsGlobeVar.localDB);
        myconnection.Open();
        DataTable table1 = new DataTable("EstGuids");

        string select = GetTaskDescription_SQLCreate();
        try
        {

            cmd = new MySqlCommand(select, myconnection);
            GetTaskDescription_ParameterFill(ref  cmd, clsGlobeVar.ClientGuid, EstmateNameGuid);

            dr = cmd.ExecuteReader();

            if (dr.HasRows)
            {                 
                table1.Columns.Add("Estimate_Guid");
                table1.Columns.Add("Estimate_Description");
                table1.Columns.Add("Estimate_Date");
                table1.Columns.Add("Active");
                string [] field = new string[5] ;

                while (dr.Read())
                {  
                    // going to read field in the row.
                    field[0] =  dr.SafeGetString(0);
                    field[1] =  dr.SafeGetString(1);
                    field[2] =  dr.SafeGetString(2);
                    field[3] =  dr.SafeGetString(3);
                      // this field does not exist but I tried to read it
                     // this should fail and raise an exception  
                     // it does fail but does not raise the exception
                    field[4] =  dr.SafeGetString(4);
                }
    }

   // this catch is ignored
catch (MySqlException ex)  
     {  some code }

// the finally block executes okay
finally  { some clean up}
// and this return statement is ignored and the code in the caller does not execute
return table1
}

感谢您的帮助。

Answer 1

通常不建议以这种方式处理异常，因为您永远无法确定嵌套代码实际抛出了哪些异常。 您至少应该为意外事件添加一个处理程序：

catch (MySqlException ex)  
 {  some code }
catch (Exception ex)
{
   //Unexpected exception thrown...
}