Hiding and Showing Columns in the DataGrid Control...

Discussion in 'ASP .Net Datagrid Control' started by Amber, Oct 7, 2003.

  1. Amber

    Amber Guest

    The DataGrid allows you to make columns visible or invisible on demand
    - even edit and other special columns. This article will show you how
    it is done.

    Some developers have reported problems controlling the visibility of
    columns in the DataGrid control. The problem usually comes down to one
    fact. The DataGrid has a property called AutoGenerateColumns. The
    default value is "True". This means that when AutoGenerateColumns is
    set to True, the DataGrid will pull its column headings straight from
    the column names of the database table. If you allow this to happen
    you cannot control the visibility of the columns. You must use
    asp:BoundColumns and specify the HeaderText and Datafield properties
    in your DataGrid setup. This relatively simple change allows you
    accomplish the hiding and showing of columns as you wish. It also
    works with Edit and other special columns as you will see.

    First, lets look at the html code in our .aspx page. Immediately below
    the
    tag we have two buttons and set OnClick event handlers to two
    subroutines which will do the work of hiding and showing the
    appropriate columns in our code-behind file. In the DataGrid code,
    notice that AutoGenerateColumns is set to "False". Also notice that we
    have used asp:BoundColumns to set our HeaderText and DataFields. I
    have also set the Visible property to false so that nothing but the
    CompanyName column will be shown at startup. I have also added an Edit
    column although I did not wire it up to actually do any editing (the
    copy of the Customers table in the Northwind database I am using is
    readonly anyway). After the bound columns are some other datagrid
    properties just to make the grid look good.



















    AutoGenerateColumns="False"
    BorderColor="#999999"
    BorderStyle="None"
    BorderWidth="1px"
    BackColor="White"
    CellPadding="3"
    GridLines="Vertical">



















    Now for the code-behind file which is shown in two parts. The first
    part displayed below is just the usual page_load event which calls a
    "BindTheData" routine to actually get the data from the Customers
    table. All of this should be self explanatory.

    Imports System.Data
    Imports System.Data.SqlClient
    Imports System.Configuration

    Public Class ShowHideCols : Inherits System.Web.UI.Page
    Protected btnShow As System.Web.UI.WebControls.Button
    Protected btnHide As System.Web.UI.WebControls.Button
    Protected dtgCusts As System.Web.UI.WebControls.DataGrid

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
    System.EventArgs) Handles MyBase.Load
    If Not IsPostBack Then
    BindTheData
    End If
    End Sub

    Sub BindTheData
    Dim objConn As SqlConnection
    Dim objCmd As SqlCommand
    objConn = New SqlConnection(ConfigurationSettings.AppSettings("NorthwindConnection"))
    Dim strSql As String
    strSql = "SELECT Top 10 CompanyName, ContactName, ContactTitle,
    City, Country, Phone FROM Customers"
    objCmd = New SqlCommand(strSql, objConn)
    objConn.Open
    dtgCusts.DataSource = objCmd.ExecuteReader()
    dtgCusts.DataBind()
    objConn.Close()
    objConn.Dispose()
    End Sub


    Lastly comes our two subroutines to handle the showing and hiding of
    the columns in the grid other than Company Name. Since Company Name is
    Column(0), these routines use a simple For...Next loop to cycle
    through the remaining columns setting the visible property to true or
    false as appropriate.

    Sub ShowDetails(sender As System.Object, e As System.EventArgs)
    Dim intCounter As Integer
    For intCounter = 1 to dtgCusts.Columns.Count - 1
    dtgCusts.Columns(intCounter).Visible = True
    Next
    End Sub

    Sub HideDetails(sender As System.Object, e As System.EventArgs)
    Dim intCounter As Integer
    For intCounter = 1 to dtgCusts.Columns.Count - 1
    dtgCusts.Columns(intCounter).Visible = False
    Next
    End Sub

    End Class


    There you have it. A simple way to control the visible property of
    your DataGrid columns.


    AMBER [MCSD.NET MCAD.NET] http://www.dedicatedsolutions.co.uk
     
    Amber, Oct 7, 2003
    #1
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  2. Amber

    Alvin Bruney Guest

    >If you allow this to happen
    > you cannot control the visibility of the columns. You must use
    > asp:BoundColumns and specify the HeaderText and Datafield properties
    > in your DataGrid setup.


    This is not correct at all. Hiding autogenerated columns is easily
    accomplished in the itemdatabound/created event handler by setting the
    Cell's visible property to false.

    Microsoft discourages developers from using the autogenerated feature except
    for prototyping. I believe this to be a flawed recommendation on their part,
    coupled to the fact that it is on by default. Developers should not fear the
    autogenerate feature of a datagrid because it is very powerful, contains
    most if not all the power of bound columns and results in a faster more
    efficient datagrid render than if bound columns were used. The false premise
    that microsoft builds on is that you do not have full control of the
    datagrid when autogenerated columns is used. This is absolutely false.
     
    Alvin Bruney, Oct 11, 2003
    #2
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