I am using below code but it's throw an error on last line

Question

4.00/5 (1 vote)

See more:

C#

protected override void Append(LoggingEvent loggingEvent)
{
    if (loggingEvent.Level.Name == "INFO")
    {
        FIXOUTUI ui = FIXOUTUI.GetInstance();
        Action action = () =>
        {
            ui.Listbox1.Items.Add(loggingEvent.TimeStamp.ToString("HH:mm:ss") + " " + loggingEvent.RenderedMessage);

            ui.Listbox1.SelectedItem = ui.Listbox1.Items[ui.Listbox1.Items.Count - 1];
            ui.Listbox1.UpdateLayout();

            var listBoxItem = (ListBoxItem)ui.Listbox1
                .ItemContainerGenerator
                .ContainerFromItem(ui.Listbox1.SelectedItem);
            listBoxItem.Focus(); this line throw an error
        };
        ui.Dispatcher.BeginInvoke(action);
    }
}

Quote:
ERROR: Unhandled Exception System.NullReferenceException:
Object reference not set to an instance of an object.
at MyApp.Delogs.<>c__DisplayClass3.b__0()
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

Posted 9-May-14 5:52am

inam2001

Updated 9-May-14 5:58am

CHill60

v2

Add a Solution

Comments

CHill60 9-May-14 11:59am

Put a break point on that line. When you get there check the values of ui.Dispatcher and action... you'll probably find the latter is Null

Matt T Heffron 9-May-14 12:30pm

Actually, action is the LEAST LIKELY thing to be null, given that it is assigned in the immediately preceding statement.

CHill60 9-May-14 12:42pm

Only if that statement worked though

Matt T Heffron 9-May-14 12:47pm

That statement is just the assignment of the lambda-form delegate.
It won't return null if it fails.
It would fail "spectacularly!" (i.e., throw an exception)
In fact, an optimizing compiler would remove the assignment altogether and just pass the reference to the delegate in the .BeginInvoke() directly.

CHill60 9-May-14 12:54pm

Ah of course. My fault for looking at it properly! Thanks

ZurdoDev 9-May-14 12:01pm

Something is null. You need to fix that.

Matt T Heffron 9-May-14 12:37pm

The most likely problem is that ContainerFromItem has returned null, listBoxItem == null.
Check out the conditions where ContainerFromItem can return null.

inam2001 9-May-14 12:41pm

Yes, obviously return null but why? and how to fix it.

Matt T Heffron 9-May-14 12:44pm

From the docs for ContainerFromItem:
Returns null if the item does not belong to the item collection, or if a UIElement has not been generated for it.

BillWoodruff 9-May-14 15:13pm

Whatever you are doing in the code:

var listBoxItem = (ListBoxItem)ui.Listbox1
.ItemContainerGenerator
.ContainerFromItem(ui.Listbox1.SelectedItem);
listBoxItem.Focus(); this line throw an error

We probably can't help you unless we know what kind of object is put into the variable 'listBoxItem. There is no 'ListBoxItem object in .NET, so you must be defining it.

Matt T Heffron 12-May-14 14:14pm

ListBoxItem DOES EXIST in WPF.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

pallelokanathareddy · Answer 1 · 2014-05-11T18:09:00

Solution 1

It looks like your ListBox (ListBox1) is not pouplated with data . debug your code .

Posted 11-May-14 18:09pm

pallelokanathareddy