如何处理 reader.GetByte(x) 中的 NULL 值？

Question

我得到了以下代码块：

//Check to see if the Unique_ID is 10 or 11 and process accordingly
//10 = Both boxes, 11 = Rework only
if (reader.GetByte(16) == 10)
{
   int ES = Convert.ToInt32(reader["ESCALATED"]);
   if (ES == 0)
   {
      chkEscalated.Checked = false;
   }
   else
   {
      chkEscalated.Checked = true;
      chkEscalated.Visible = true;
      lblEscalated.Visible = true;
      chkRework.Visible = true;
      lblRework.Visible = true;
    }
}
else if (reader.GetByte(16) == 11)
{
}
else
{
}

我遇到的问题是，有时 reader.GetByte(16) 为 NULL。当发生这种情况时，我得到一个错误：

Data is Null. This method or property cannot be called on Null values.

我还是个新手，所以我确定我缺少一些明显的东西，但我就是找不到。

Answer 1

如果你错过了第一个 if，你真的要读 2 遍吗？也许这就是问题所在。将值存储为 var a = reader.GetByte(16) 并查找该值。像这样：

//Check to see if the Unique_ID is 10 or 11 and process accordingly
//10 = Both boxes, 11 = Rework only 
var a = reader.GetByte(16);
if(a != null)
{
   if (a == 10)
   {
      int ES = Convert.ToInt32(reader["ESCALATED"]);
      if (ES == 0)
      {
         chkEscalated.Checked = false;
      }
      else
      {
         chkEscalated.Checked = true;
         chkEscalated.Visible = true;
         lblEscalated.Visible = true;
         chkRework.Visible = true;
         lblRework.Visible = true;
       }
   }
   else if (a == 11)
   {
   }
   else
   {
   }
}

Answer 2

根据您发布的错误消息，似乎有时 reader 未初始化。 reader 是否在某处被填充或初始化？如果是，那是检查的好地方。错误消息仅表示 reader 未引用现有实例，因此它为 NULL，因此您不能对其调用方法，即您不能在其中调用 GetByte()

Answer 3

你可以在if语句中添加if (reader.GetByte(16) != null && reader.GetByte(16) == 10) 这将检查 reader.GetByte(16) 是否为 null

Answer 4

if(!String.IsNullOrEmpty(reader.GetByte(16).ToString()))
{
if (reader.GetByte(16) == 10)
{
   int ES = Convert.ToInt32(reader["ESCALATED"]);
   if (ES == 0)
   {
      chkEscalated.Checked = false;
   }
   else
   {
      chkEscalated.Checked = true;
      chkEscalated.Visible = true;
      lblEscalated.Visible = true;
      chkRework.Visible = true;
      lblRework.Visible = true;
    }
}
else if (reader.GetByte(16) == 11)
{
}
else
{
}
}

试试这个。

Answer 5

使用IsDBNull方法：

//Check to see if the Unique_ID is 10 or 11 and process accordingly
//10 = Both boxes, 11 = Rework only
if (reader.IsDBNull(16))
{
   //Add here your code to handle null value
}
else
{
   //Use a switch to read the value only one time
   switch (reader.GetByte(16))
   {
     case 10:
       int ES = Convert.ToInt32(reader["ESCALATED"]);
       if (ES == 0)
       {
          chkEscalated.Checked = false;
       }
       else
       {
          chkEscalated.Checked = true;
          chkEscalated.Visible = true;
          lblEscalated.Visible = true;
          chkRework.Visible = true;
          lblRework.Visible = true;
        }
        break;

      case 11:
        break;

      default:
        break;
   }
}

如何处理 reader.GetByte(x) 中的 NULL 值？

How to handle a NULL value in reader.GetByte(x)?

c#

datareader

code-behind