system.null引用异常 [英] system.null reference exception

问题描述

我在行中收到以下错误

con = new SqlConnection（ConfigurationManager.ConnectionStrings [Connect]。ToString（））;下面的代码...



错误：

system.nullreferenceexception对象引用未设置为对象的实例。

i m getting the following error in the line
"con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connect"].ToString());" of code below...

Error:
"system.nullreferenceexception object reference not set to an instance of an object."

public partial class _Default : System.Web.UI.Page
{
    SqlDataAdapter da;
    DataSet ds = new DataSet();
    SqlCommand cmd = new SqlCommand();
    SqlConnection con;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            BindData();
        }
    }
    public void BindData()
    {
        con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connect"].ToString());//getting error in this line
        cmd = new SqlCommand("Select * from b_asset_master", con);
        cmd.Connection = con;
        da = new SqlDataAdapter(cmd);
        da.Fill(ds);
        con.Open();
        cmd.ExecuteNonQuery();
        Grid.DataSource = ds;
        Grid.DataBind();
        con.Close();
    }
    protected void Grid_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
    {
        Grid.CurrentPageIndex = e.NewPageIndex;
        BindData();
    }
}

推荐答案

con = new SqlConnection(ConfigurationManager.ConnectionStrings["Connect"].ToString());//getting error in this line

你正在使用的这行

in this line you are using

ConfigurationManager.ConnectionStrings["Connect"].ToString()

但我认为配置文件中不存在连接键。或者你在那里使用了错误的法术。

but i think "Connect" key dose not exist in your config file. or you using wrong spell there.

它取决于它在哪一行，但最明显的候选者是：

It depends which line it is on, really, but the most obvious candidate is:

cmd.CommandText = "Select * from b_asset_master";

如果您没有为cmd分配值，那么您将收到此错误。

尝试将其更改为：

If you have not assigned a value to cmd, then you will get this error.
Try changing it to:

cmd = new SqlCommand("Select * from b_asset_master", con);

并丢弃后面的行。问题应该消失。



当你遇到这样的问题时，首先要做的是查看调试器中的代码，找到变量 null - 您通常可以很容易地从您需要做的事情中解决。它比很多，比每次问这里快得多！ ：笑：

and discard the line after it. The problem should go away.

When you get a problem like this, the first thing to do is look at the code in the debugger, and find the variable that is null - you can usually work out pretty easily from that what you need to do. And it's a lot, lot quicker than asking here each time! :laugh:

ds 来自哪里？看起来是 null 。

Where does that ds come from? Looks like that is null.

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