Hidden field after sort - asp.net

Question

Apparently something is lost when a change is made to my RadioButtonList and the GridView is sorted. I guess this is a post back.
<asp:GridView ID="GridView1"
datasourceid="CoffeeDS"
runat="server"
autogeneratecolumns="False"
allowsorting="True">
<Columns>
<asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />
<asp:BoundField DataField="Brand" HeaderText="Brand" SortExpression="Brand" />
<asp:BoundField DataField="Roast" HeaderText="Roast" SortExpression="Roast" />
<asp:BoundField DataField="Type" HeaderText="Type" SortExpression="Type" />
<asp:BoundField DataField="Description" HeaderText="Description" SortExpression="Description" />
<asp:BoundField DataField="RowColor" HeaderText="RowColor" Visible="false" />
</Columns>
</asp:GridView>
protected void Page_Load(object sender, EventArgs e)
{
AddLineColor();
}
private void AddLineColor()
{
GridView1.DataKeyNames = new string[] { "RowColor" };
for (int i = 0; i< GridView1.Rows.Count; i++)
{
GridView1.Rows[i].BackColor = Color.FromName(GridView1.DataKeys[i]["RowColor"].ToString());
}
}
protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
{
GridView1.Sort(RadioButtonList1.SelectedValue, SortDirection.Ascending);
AddLineColor();
}
When the page loads the colored rows appear as expected, however when SelectedIndexChanged runs the data sorts correctly but no colors appear. I thought that resetting DataKeyNames would do the trick but no joy. It seems the hidden field just evaporates.
I am coming from vb.net and WinForms so this is doubly frustrating.
This is plain old asp.net as I chose to host on GoDaddy for practice. They do a bit of core but I haven't figured out what version yet.

Answer 1

Ok, first up?
In Vb6, vb.net, ms-access, even FoxPro - and just about any desktop enviroment?
We setup the grid, the controls etc. on FIRST page load. (we always did - on load event).
Now, in asp.net? Yes, we quite much do the same. But there is some ugly grinds in the coffee that we have to be aware of:
Every button, every event, every click? The page load event fires EACH time again!!!
So, that means our page load event is "sort of" what we were used to in the page, but it fires EVERY time!!!
So, that means to load up the grid? Well, ok, we put our code in the page load event. But we want to think, to play, to code like we always did? And this desire is not only due to how we coded in the past, but that we need/want/should have the same concept on page load - the FIRST page load.
So, you want to always - without thought - ALWAYS code a REAL page load event - one that only runs the first time.
And you do that with this on the page load event:
If Not IsPostBack Then
End if
or if we going with c#, then:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPost Back)
{
AddLineColor();
}
}
that way, our grid load fires one time. Remember, you touch + click ANY button on that page with a post-back? The page load event fires. So it not really our lovable page load like you used since your first day of coding! But, by a simple test for IsPostBack = False, then the code inside of that REALLY does become our true page load event like our minds have coded for "years" without thinking.
So, put in that real page load code stub.
And I would consider writing code to fill out that GridView in place of the wizards and it then inserting a "data source" into the markup. It not a huge deal.
So, if the RadioButton has a auto post back? then on-load will fire, your custom format routine will fire, and THEN teh code stub event for your radio button will fire.
So, if you want the formatting to trigger/run when you change/set a raadio button (assuming auto post-back), then you need to call the color formatting routine AFTER again (in the RadioButtion index changed event.
However, given the typical flow of code in a asp.net web page?
I would move your formatter to the row data bound event.
I OFTEN will drop in a grid view. Often will use the wizard to setup and create the grid view. I then delete the datasource on the page, remove the gridview setting for that data source (DataSourceID = "sqlDataSource1"), and then code out the data load myself.
I do this for several reasons - and one is to gain control over the data loading process, only have it load ONE time on now what we call our REAL page load event.
DataKeys:
I not 100% sure - but it looks like (seems like) you using DataKeys for somthing other then what they are for. DataKeyes are for the PK row ID. This allows you to toss up a nice grid, but NOT have to expose/have the PK row id in the markup for the grid control. In other words, I would not re-purpose it for some other use.
Of course the common issue then crops up: How do I deal with and have columns from the database in my code that I do NOT want to dispay on the grid, but I need for foramtting, maybe some calulation. Or maybe just that you click on a row and then want to jump to a page to edit/show the details for that one record. So the DataKeys list is for holding the PK value - but not having it displayed in the markup, or the PK having to be a column of data for display.
So, it not quite clear your use of Datakeys here?
But, if you looking to format/change color or whatever in that grid? I would move your color format routine you have to the row data bound event. This means a code change, but that event is some what better, since during the row data bound event, you have FULL USE of the actual data row used to bind - and that includes columns that you don't display in the markup (grid), but is part of the data source you used.
So, my typical code to bind/load a grid looks like this:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack) {
LoadGrid();
}
}
void LoadGrid()
{
using (SqlCommand cmdSQL = new SqlCommand("SELECT Animal, ImageB from tblAnimals",
new SqlConnection(Properties.Settings.Default.TEST4)))
{
cmdSQL.Connection.Open();
GridView1.DataSource = cmdSQL.ExecuteReader();
GridView1.DataBind();
}
}
I can expand on that issue - but lets just be all warm and happy that we are now coding like we did in the past with a REAL page load event (inside of that "if IsPostBack = False).
In fact, the FIRST thing I do for any web page on page load? I write in that !IsPostback stub - and I can't think of out of 100's of web pages that is missing that code stub - they all have them!
Edit: ----------------------
Ok, so we adopted a data table as per above. Now, lets format each row of the grid. As noted, we will/should/near always/ use the on data bound event. And there are MANY reasons, but one BIG bonus reason is that we have FULL use of the actual data row columns during that bind process. And that INCLUDES columns in the data source that we not going to display in the grid. (but, we sure might want to use some of those non displayed columns for things like formatting the grid).
So, with above code we load the grid. But now lets add the formatting code.
First up? We can't JUST stuff cmdSQL.Execute reader into the grid anymore (becuase I need the full row during biding).
So, the code to load the grid in above now becomes this:
void LoadGrid()
{
using (SqlCommand cmdSQL = new SqlCommand("SELECT * from tblhotels ORDER BY HotelName",
new SqlConnection(Properties.Settings.Default.TEST4)))
{
cmdSQL.Connection.Open();
DataTable rst = New DataTable()
rst.Load(cmdSQL.ExecuteReader());
GridView1.DataSource = rst;
GridView1.DataBind();
}
}
So, yes, we NOW need to fill the grid via table - we can't use reader,, since during data bind I want/need that data.
So, now our formatting code goes in the row data bind event. Lets say we want a blue color for the row for City = "Edmonton". NOTE BEYOND great is that I don't even have to show/have that city in the grid - we have FULL use of the FULL data row. The code in row bind now looks like this:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
// get the full data row - all columns
DataRowView OneRow = (DataRowView)e.Row.DataItem;
// if the city is Edmonton, format row to blue
// note that CITY IS NOT in the grid view display!!!!
if ((string)OneRow["City"] == "Edmonton")
{
e.Row.BackColor = System.Drawing.Color.AliceBlue;
}
}
}
So note how we are now able to get FULL use of the SAME row used during the bind process.
so, say our markup does NOT have the city, say like this:
<asp:GridView ID="GridView1" runat="server" CssClass="table table-hover"
AutoGenerateColumns="False" OnRowDataBound="GridView1_RowDataBound" >
<Columns>
<asp:BoundField DataField="FirstName" HeaderText="FirstName" SortExpression="FirstName" />
<asp:BoundField DataField="LastName" HeaderText="LastName" SortExpression="LastName" />
<asp:BoundField DataField="HotelName" HeaderText="HotelName" SortExpression="HotelName" />
<asp:BoundField DataField="Province" HeaderText="Province" SortExpression="Province" />
</Columns>
</asp:GridView>
When we run the above code, we now get this:
So, we have full use of all columns during that databind process. Just remember, once data bind has completed, then we DO NOT have use of the GridView1.DataSource, but we certainly do during the bind process, and thus I was able to get "OneRow" as per above.

Answer 2

Ok, as stated. We can't hide a control in the grid with Visible = False. Now for 20+ years using a rather wide varity of desktop tools? We often did that. But, in web land? Nope! - if you set a control.Visible = False, it not only hides the control but the asp.net redering engine will ALSO skip that control! It does not exist in the markup. In fact, even during itemDatabound, you note that the cell that points to that column is blank (empty). Was surpised that you could even use that control. So as a general rule, you can't use Visible = False for anything more then hiding a control - but if you hide, then as a "general" rule, then you can't use that control and get/grab values from it. It just the way the web works.
So, to hide a control, then Style="display:none" is the general workaround. However, (I did not realize) that boundfield controls do NOT support Style - so, no suggesting to put it else where - it just don't work (my bad, my fault - bad suggestion here).
next up:
As stated, as a general rule, you can after you bind up the whole data grid loop again and do formatting against the grid, however, it MUCH better to do this on the item data bound event. So, to setup extra values, hide/show, set values, and of course setup colors for a single text box, or the whole row? That code belongs in row data bind event. And better yet, it ALSO solves the whole problem of getting at the WHOLE data row set of values. Including often things like the PK, or say your color color - they do NOT have to be part of the markup - but ONLY part of the data source you use to bind the grid.
So, quite much a "good" guess and "good" idea? Do grid formatting in the row data bound event - it again like the visbile sugesting is just a good idea - and this approch means you don't fight the event model, but leverage it to your advantage.
I also don't know what type or thing DataAccess is - but again, not a huge deal, since you do eventually move/get/have a data table to work with.
As a small FYI: A .net datatable has ALWAYS had a built in data view object. This suggests that we really don't need to create a whole new DataView object/instance. But, lets just go along, and create that dataView anyway.
So, we need one routine - it loads the grid.
Say like this:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
LoadGrid();
}
}
void LoadGrid(string MySort = "")
{
// load up our grid
DataTable rst = new DataTable();
rst = DA.DT(); // ????
DataView MyView = new DataView(rst);
MyView.Sort = MySort;
GridView1.DataSource = MyView;
GridView1.DataBind();
}
And, our data bind even to foramt:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
// get the full data row - all columns
DataRowView OneRow = (DataRowView)e.Row.DataItem;
// fomrat the row based on color
e.Row.BackColor = (string)OneRow["Color"]
}
}
(check the type for color - I don't know if that is a string in your case???)
And the sorting code?
private void SortGrid(int Index)
{
GridView1.DataSource = null;
switch (Index)
{
case 0: //Alphabetical
break;
case 1: //Type
LoadGrid("Type ASC");
break;
case 2: //Brand
LoadGrid("Brand ASC");
break;
case 3: //Roast
LoadGrid("Roast ASC");
etc.
So, remove the color bound field from the grid markup - we don't need it.

Answer 3

As Albert D. Kallal suggested, I added the check for IsPostback. I go rid of the SqlDataSource, datasourceid, and went back to my good old DataTable retrieved from a DataAccess class. I tried the DataKey because it seemed to preserve my hidden RowColor column. It worked for page load but not after. The DataSourceID made the code to sort easy but I lost access to RowColor.
Finally saw the light and got the RowDataBound working. I didn't realize that you could access the underlying datasource in this event but that is exactly what DataItem does. This greatly simplified the code and is more efficient to format in RowDataBound rather than looping through all the rows.
Thanks to Albert D. Kallal for his patience and great explanations.
<asp:GridView ID="GridView1"
runat="server"
autogeneratecolumns="False"
allowsorting="True"
OnRowDataBound="CustomersGridView_RowDataBound">
<Columns>
<asp:BoundField DataField="Name" HeaderText="Name" SortExpression="Name" />
<asp:BoundField DataField="Brand" HeaderText="Brand" SortExpression="Brand" />
<asp:BoundField DataField="Roast" HeaderText="Roast" SortExpression="Roast" />
<asp:BoundField DataField="Type" HeaderText="Type" SortExpression="Type" />
<asp:BoundField DataField="Description" HeaderText="Description" SortExpression="Description" />
</Columns>
</asp:GridView>
public partial class _Default : Page
{
private DataAccess DA = new DataAccess();
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
LoadGrid();
}
}
protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
{
SortGrid(RadioButtonList1.SelectedIndex);
}
private void SortGrid(int Index)
{
GridView1.DataSource = null;
switch (Index)
{
case 0: //Alphabetical
LoadGrid();
break;
case 1: //Type
LoadGrid("Type ASC");
break;
case 2: //Brand
LoadGrid("Brand ASC");
break;
case 3: //Roast
LoadGrid("Roast ASC");
break;
default: //Alphabetical
LoadGrid();
break;
}
}
protected void GridView1_RowDataBound(Object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
//DataItem gets underlying data object
DataRowView OneRow = (DataRowView)e.Row.DataItem;
e.Row.BackColor = Color.FromName(OneRow["RowColor"].ToString());
}
}
void LoadGrid(string MySort = "")
{
DataTable dt = new DataTable();
dt = DA.DT;
DataView MyView = new DataView(dt);
MyView.Sort = MySort;
GridView1.DataSource = MyView;
GridView1.DataBind();
}
}
The DataAccess class...
public class DataAccess
{
public DataAccess()
{
FillCoffeeData();
}
public DataTable DT { get; set; }
private string ConStr = "*****"
private void FillCoffeeData()
{ //0 1 2 3 4 5
string sql = #"Select Coffees.[Name], Roasters.[Name] As Brand, Coffees.Roast, Coffees.[Type], Coffees.[Description], RowColor
FROM Coffees
INNER JOIN Roasters ON Coffees.RoasterID = Roasters.ID
Order By Coffees.[Name], Roasters.Name";
DT = new DataTable();
using (SqlConnection cn = new SqlConnection(ConStr))
using (SqlCommand cmd = new SqlCommand(sql,cn))
{
cn.Open();
using (SqlDataReader reader = cmd.ExecuteReader())
{
DT.Load(reader);
}
}
}
}