需要处理空异常

Question

private int MyTimeValue()
{
    int Value = 0;
    string connectionString = GetConfigurationSettingValue("ConnectionString");
    int Days = 120;
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();
        using (SqlCommand cmd = new SqlCommand("select [dbo].[My_function] (@Span)", connection))
        {
            cmd.CommandType = System.Data.CommandType.Text;
            cmd.Parameters.Add(new SqlParameter("@Span", Days));
            Value = Convert.ToInt32(cmd.ExecuteScalar());
        }
    }
    return (Value);
}

我越来越Object cannot be cast from DBNull to other types.

如何使用try和catch处理此处的空异常

请帮助我语法。

Answer 1

您可以在转换前进行验证

object result = cmd.ExecuteScalar();
if(result != null)
    Value = Convert.ToInt32(result);

并添加参数如下

 cmd.Parameters.AddWithValue("@Span", Days);

作为旁注，不需要第 cmd.CommandType = System.Data.CommandType.Text; 行。 默认命令类型为文本

Answer 2

我想

错误就在这里：

Value = Convert.ToInt32(cmd.ExecuteScalar());

试试这个：

var result = cmd.ExecuteScalar();
Value = result == DBNull.Value ? 0 : Convert.ToInt32(result);

注意：您的命令字符串对我来说似乎也是错误的。

Answer 3

您需要首先检查 ExecuteScalar 返回的值是否为 null，以便在尝试将对象强制转换为 Int32 时不会发生异常。

private int MyTimeValue()
    {
        int Value = 0;
        string connectionString = GetConfigurationSettingValue("ConnectionString");
        int Days = 120;
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();
            using (SqlCommand cmd = new SqlCommand("select [dbo].[My_function] (@Span)", connection))
            {
                cmd.CommandType = System.Data.CommandType.Text;
                cmd.Parameters.Add(new SqlParameter("@Span", Days));
                object o=cmd.ExecuteScalar();
                if(o!=null)
                   Value = Convert.ToInt32(o);
            }
        }
        return (Value);
    }

Answer 4

这可以通过两种方式完成。

案例 1：处理特定异常

private int MyTimeValue()
{
    int Value = 0;
    try
    {      
       string connectionString = GetConfigurationSettingValue("ConnectionString");
       int Days = 120;
       using (SqlConnection connection = new SqlConnection(connectionString))
       {
           connection.Open();
           using (SqlCommand cmd = new SqlCommand("select [dbo].[My_function] (@Span)", connection))
           {
               cmd.CommandType = System.Data.CommandType.Text;
               cmd.Parameters.Add(new SqlParameter("@Span", Days));
               Value = Convert.ToInt32(cmd.ExecuteScalar());
           }
       }
     catch(NullReferenceException ex)
     {
        \Handle Exception
     }
     return (Value);
}

情况 2：检查变量是否为 Null，并捕获其他意外异常的常规异常

    private int MyTimeValue()
{
    int Value = 0;
    try
    {      
       string connectionString = GetConfigurationSettingValue("ConnectionString");
       int Days = 120;
       using (SqlConnection connection = new SqlConnection(connectionString))
       {
           connection.Open();
           using (SqlCommand cmd = new SqlCommand("select [dbo].[My_function] (@Span)", connection))
           {
               cmd.CommandType = System.Data.CommandType.Text;
               cmd.Parameters.Add(new SqlParameter("@Span", Days));
               var result = cmd.ExecuteScalar();
               if(result !=null)
                    Value = Convert.ToInt32(result );
           }
       }
     catch(Exception ex)
     {
        \For handling unexpected exceptions
     }   
     return (Value);
}

Answer 5

试试这个

          Value = cmd.ExecuteScalar();    
          if (((Value != null) || (Value != DBNull.Value)))
          {
          Value =(int)Value ;
          }