Object reference not set to an instance of an object

GridView RowDataBound Alternating Row RowState issue

2008-10-27T12:38:00Z

This was pissing me off for a good hour: RowDataBound event after you call edit on a row, I was checking for this row's state like this:

e.Row.RowState == DataControlRowState.Edit

this worked fine with rows No 1, 3, 5... (non-alternating rows), however with alternating rows of same GridView it did NOT work as their RowState is something like "Alternate | Edit". RowState contains more than one value using bit-logic. See DataControlRowState Enumeration

the solution is as follows:

((e.Row.RowState & DataControlRowState.Edit) > 0)

A triangle in html

2008-10-23T13:57:00Z

Guess how? No image involved, pure html!

your own custom event delegate

2008-08-07T15:15:00Z

in MyControl:

public delegate void MyEventHandler(int value, string text);

public event MyEventHandler MyEvent;

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)

{

MyEvent(((DropDownList)sender).SelectedIndex, ((DropDownList)sender).SelectedItem.Text);

}

in Parent:

this.MyControl.MyEvent += new AAL.FreedomWeb.Web.UI.UserControls.AircraftConfig.MyEventHandler(MyControl_MyEvent);

private void MyControl_MyEvent(int value, string text)

{

throw new NotImplementedException();

}

string to enum

2008-04-24T10:05:00Z

How do you convert a string into an enumeration?

object Enum.Parse(System.Type enumType, string value, bool ignoreCase);

example:

enum Colour

{

Red,

Green,

Blue

}

Colour c = (Colour) Enum.Parse(typeof(Colour), "Red", true);

Console.WriteLine("Colour Value: {0}", c.ToString());

source: http://blogs.msdn.com/tims/archive/2004/04/02/106310.aspx

When AJAX ScriptManager is on MasterPage

2008-03-13T15:00:00Z

..and we need to access it:

ScriptManager ScriptManager1 = (ScriptManager)Master.FindControl("ScriptManager1");
ScriptManager1.AsyncPostBackTimeout = 300;

..or a much beter way:

ScriptManager ScriptManager1 = ScriptManager.GetCurrent(this);

suggested by rajbk

JavaScript img preload

2008-03-04T10:39:00Z

Not sure if this is the best method, but this is the one I used to preload the image.

if (document.images)

{

imgPreload = new Image();

imgPreload.src = "../Images/ajax-loader.gif";

}

</script>

Sort a ListBox

2008-02-19T11:16:00Z

I believe this method is available in .NET 3.5, but in earlier framework versions we have to implement this ourselves..
 
#region Helper functions
 
    /// <summary>
    /// Sorts the list box in descending order
    /// </summary>
    /// <param name="pList">the list to sort</param>
    /// <param name="pByValue">Sort the list by values or text</param> 
private void sortListBox(ref ListBox pList, bool pByValue)
{
    SortedList lListItems = new SortedList();
 
    //add listbox items to SortedList 
    foreach (ListItem lItem in pList.Items)
    {
        if (pByValue) lListItems.Add(lItem.Value, lItem);
        else lListItems.Add(lItem.Text, lItem);
    }
 
    //clear list box
    pList.Items.Clear();
 
    //add sorted items to listbox
    for (int i = 0; i < lListItems.Count; i++)
    {
        pList.Items.Add((ListItem)lListItems[lListItems.GetKey(i)]);
    }
}
 
    #endregion
}

CSV to TextReader

2008-02-19T11:11:00Z

/// <summary>
/// Take a file path and return a TextReader
/// </summary>
/// <param name="file_path"></param>
/// <returns></returns>
private TextReader OpenFile (string file_path)
{
    try
    {
        // Read the CSV file in to a TextReader
        TextReader _rdr = File.OpenText(file_path);
        // Set file attributes
        File.SetAttributes(file_path, FileAttributes.Normal);
 
        return _rdr;
    }
    catch (Exception)
    {
        throw new Exception(String.Format(
                "Error trying to open file {0}. Check file exists and is accessible<br /><br />" +
                "Possible Issues:<br/><br />Files cannot be accessed via mapped network drives" + 
                "<br />The file is open<br />The file has been viewed and then saved in Excel",file_path));
    }
}

AJAX UpdatePanel triggers, Conditional update mode

2008-02-07T10:53:00Z

First of all I'd like to thank kowalskec for pointing me out the CopySourceasHTML VS add-in that will help me copy the code snippets from Visual Studio here without losing any text formatting.

Cheers buddy! =)

And now the task:

The BugsGridView GridView control and BugsListTimeLabel Label in the Default.aspx page are encapsulated inside an UpdatePanel with an ID of BugsListUpdatePanel. The UpdatePanel does not update when other UpdatePanels on the page generate postbacks.
The ActivityLabel Label control in the Default.aspx page is encapsulated inside an UpdatePanel with an ID of ActivityUpdatePanel. The UpdatePanel does not update when other UpdatePanels on the page generate postbacks. This UpdatePanel does not contain any other controls.
The ActivityUpdatePanel UpdatePanel control in the Default.aspx page defines a trigger which causes the UpdatePanel to asynchronously refresh when the Click event of the ClearButton Button is raised.
The BugsGridView_RowUpdated event handler in the _Default partial class refreshes the ActivityUpdatePanel UpdatePanel if changes have been made to the BugsGridView GridView control.

This will help me remember how to make the UpdatePanel do a postback by clicking a button outside of the panel, as well as call the UpdatePanel Update() method from code behind.

<!--

Done:

The Default.aspx page contains a ScriptManager control with an ID of

BugsPageScriptManager.

-->

<asp:ScriptManager ID="BugsPageScriptManager" runat="server" EnablePartialRendering="true" />

<!--

Done:

The BugsGridView GridView control and BugsListTimeLabel Label in the

Default.aspx page are encapsulated inside an UpdatePanel with an ID of

BugsListUpdatePanel. The UpdatePanel does not update when other

UpdatePanels on the page generate postbacks.

-->

<asp:UpdatePanel ID="BugsListUpdatePanel" runat="server" UpdateMode="Conditional">

Bugs as of:

<asp:Label ID="BugsListTimeLabel" runat="server" Text="" />

<asp:GridView ID="BugsGridView" runat="server" AutoGenerateColumns="False" AutoGenerateEditButton="True"

DataSourceID="BugsDataSource" OnRowUpdated="BugsGridView_RowUpdated">

</asp:GridView>

</ContentTemplate>

</asp:UpdatePanel>

<!--

Done:

The ActivityLabel Label control in the Default.aspx page is encapsulated

inside an UpdatePanel with an ID of ActivityUpdatePanel. The UpdatePanel

does not update when other UpdatePanels on the page generate postbacks.

This UpdatePanel does not contain any other controls.

-->

<!--

Done:

The ActivityUpdatePanel UpdatePanel control in the Default.aspx page

defines a trigger which causes the UpdatePanel to asynchronously refresh

when the Click event of the ClearButton Button is raised.

-->

<asp:UpdatePanel ID="ActivityUpdatePanel" runat="server" UpdateMode="Conditional">

<asp:Label ID="ActivityLabel" runat="server" />

</ContentTemplate>

<asp:AsyncPostBackTrigger ControlID="ClearButton" EventName="Click" />

</Triggers>

</asp:UpdatePanel>

<asp:Button ID="ClearButton" runat="server" Text="Clear"

OnClick="ClearButton_Click" />

    protected void BugsGridView_RowUpdated(object sender, GridViewUpdatedEventArgs e)
    {
        if (CheckForChanges(e, "Description", "Status", "AssignedTo"))
        {
            // Done:
            // The BugsGridView_RowUpdated event handler in the _Default partial class
            //  refreshes the ActivityUpdatePanel UpdatePanel if changes have been made
            //  to the BugsGridView GridView control.
 
            ActivityUpdatePanel.Update();
        }
    }

Add new Blog Post WYSIWYG horrors

2008-02-06T10:51:00Z

First of all, I am not even talking about FireFox or Opera, it's IE6 what I try to use to make a new post. I copy-paste the code from Visual Studion or even do it through Word, but there's no way I can get the same look of code snippets:

This is copied straight from VS:

/// <summary>

/// Initialises webpage.

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

protected void Page_Load(object sender, System.EventArgs e)

{

...

{

}

else

{

...

}

And this - VS -> Word -> Here:

/// <summary> /// Initialises webpage. /// </summary> /// <param name="sender"></param> /// <param name="e"></param> protected void Page_Load(object sender, System.EventArgs e) { DateTime theDate = DateTime.Parse("1 January 2007"); if( !IsPostBack ) {… } else { … }

}

The 1st is too much spacing between lines, 2nd looks OK even when I do a Preview here, I do get what I see, but, once I post it, it would wrap everything horribly, so in fact What You See Is Not What You Get (WYSINWYG)