当我想加载另一个页面时，为什么会激活Page_Load事件？

Question

Very new to ASP, and I have what feels like a very basic question. I have the following code in my default.aspx.cs file:

        protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //Get one day ago
            DateTime oneDayAgo = DateTime.Now.ToLocalTime().AddDays(-1);
            String strOneDayAgo = oneDayAgo.ToString();

            //Declare the query string
            String queryString = "Select * from Computers Where whenCreated >= '" + strOneDayAgo + "' ORDER BY whenCreated DESC";

            //Show the query being used to the user
            lblQueryUsed.Text = queryString;

            // Run the query and bind the resulting DataSet to the GridView control.
            DataSet ds = GetData(queryString);
            if (ds.Tables.Count > 0)
            {
                GridView1.DataSource = ds;
                GridView1.DataBind();
            }
        }
    }

All of that works very nicely, but the problem is when a user clicks a link on that page to go to another page called Reports.aspx, that same Page_Load event fires, and all of the controls (lblQueryUsed, GridView1) are set to NULL for some reason, and I get an exception.

Why is the Page_Load event for default.aspx loading when I want to load Reports.aspx? Why are the controls null?

Thanks a lot for the help.

EDIT:Here is the full code of that page, what else do you need?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.DirectoryServices;
using System.Data.SqlClient;
using Sorter;
using System.Data;

namespace AD_watcher_web_app
{
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //Get one day ago
            DateTime oneDayAgo = DateTime.Now.ToLocalTime().AddDays(-1);
            String strOneDayAgo = oneDayAgo.ToString();

            //Declare the query string
            String queryString = "Select * from Computers Where whenCreated >= '" + strOneDayAgo + "' ORDER BY whenCreated DESC";

            //Show the query being used to the user
            lblQueryUsed.Text = queryString;

            // Run the query and bind the resulting DataSet to the GridView control.
            DataSet ds = GetData(queryString);
            if (ds.Tables.Count > 0)
            {
                GridView1.DataSource = ds;
                GridView1.DataBind();
            }
        }
    }

    protected void Label1_PreRender(object sender, EventArgs e)
    {
        //Populate the labels
        lblCompCount.Text = GridView1.Rows.Count.ToString();
        lblTimeRun.Text = DateTime.Now.ToLocalTime().ToString();
    }

    ///////////////////////METHODS///////////////////////

    DataSet GetData(String queryString)
    {
        // Set the connection string
        SqlConnectionStringBuilder conBuilder = new SqlConnectionStringBuilder();
        conBuilder.DataSource = "dbsql01dev.llnl.gov";
        conBuilder.InitialCatalog = "XloadDB";
        conBuilder.IntegratedSecurity = true;

        String connectionString = conBuilder.ConnectionString;

        //Declare a new dataset
        DataSet ds = new DataSet();

        try
        {
          // Connect to the database and run the query.
          SqlConnection connection = new SqlConnection(connectionString);        
          SqlDataAdapter adapter = new SqlDataAdapter(queryString, connection);

          // Fill the DataSet.
          adapter.Fill(ds);
        }
        catch(Exception ex)
        {
          // The connection failed. Display an error message.
            lblExceptions.Text = ex.ToString();
            lblExceptions.Visible = true;
        }
        return ds;
      }
}
}

Answer 1

For server side controls to work, the page needs to reload before the control events fire.

This is part of the page lifecycle .

This behaviour will also occur on server side links - once a postback occurs, the page reloads and page_load fires.

To avoid this, make your links into pure client side links.

So, no runat="server" , but proper HTML <a href="">link</a> links.