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Global objects in C# ASP.Net - always null when read back

In an ASP.Net project, using C#, I have a class (PlcComms.cs) for talking to a Controller (a PLC).
I want the one class object to be globally available, for each web page in my project.
I see from reading various forum posts that I should be able to create a public static object of my class type, i.e. PlcComms, in Global.asax.cs, or in a class in the App_Code folder. I've tried both and I write to the object ok, but when I go to read from it (from a timer in an update panel on the home web page) then it always read back as null.
I'm at a loss to know what to do at this point. can anyone help?
Currently, this is a class I have in the App_Code folder...
namespace SpearheadWeb
{
public static class AppGlobal
{
public static SpearheadWeb.PlcComms PlcCommsObject { get; set; }
}
}
this I have on my web page - it seems to create the object OK...
namespace SpearheadWeb
{
public partial class _Default : Page
{
private PlcComms CurrentPLC;
//some other here including ComPorts
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
try
{
//some settings reading and setup here
CurrentPLC = new PlcComms(Global.CommsSettings.CpuType1,Global.CommsSettings.Network1,ComPorts[0], Global.CommsSettings.IPAddress1, Global.CommsSettings.Path1,UpdatePanel.Controls[0].Controls, 1, Global.CommsSettings.MsUpdate1);
AppGlobal.PlcCommsObject = CurrentPLC;
but in my timer (the timer within an updatepanel) PLCComms1 is always null here...
protected void TimerUpdate_Tick(object sender, EventArgs e)
{
PlcComms PLCComms1 = AppGlobal.PlcCommsObject;

Execute same function on every page in Xamarin.Forms

I have a function that I need to perform to do some checks (e.g: CheckForUpdate, CheckNetworkConnection, CheckUserAuthorization, ...) on every page appearing or somehow before user request completed.
so I made a c# class and called it BasePage.cs:
public static class BasePage
{
public static async void CheckForUpdate()
{
// actual codes to check for updates are not included here
// just a sample alert
await App.Current.MainPage.DisplayAlert("Update", "There is a new version avaiable to update, would you like to download?", "Download", "Skip");
}
}
and used it in my pages like below:
LoginPage.cs
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class LoginPage : ContentPage
{
public LoginPage()
{
InitializeComponent();
}
protected async override void OnAppearing()
{
await Task.Run(() => BasePage.CheckForUpdate());
}
}
I don't know if this is best practice or not (I guess not) but it's not displaying alert anyhow.
so my question is what is the best way to execute functions on every page and why the code above doesn't work.

Your code doesn't seem to run on UI thread. Just use Device.BeginInvokeOnMainThread, try like below
protected override void OnAppearing()
{
Device.BeginInvokeOnMainThread(() => {
BaseClass.CheckForUpdate();
});
}
Hope it help you.

How can I make a windows service run some code if it had to restart after a crash?

Let's say a windows service crashes, and automatically restarted due to some recovery options. I want to run some code in the program (C#) that will do some network action (send an alert that it shut down) whenever this happens.
Is there an event I can apply or code I can have run after that occurs?
Thanks!

In this situation what I would do is instead of having something that gets written out when the program fails, have the program write out some kind of record to persistent storage that it then deletes if it detects a clean shutdown is being done.
public partial class MyAppService : ServiceBase
{
protected override void OnStart(string[] args)
{
if(File.Exists(Path.Combine(Path.GetTempPath(), "MyAppIsRunning.doNotDelete"))
{
DoSomthingBecauseWeHadABadShutdown();
}
File.WriteAllText(Path.Combine(Path.GetTempPath(), "MyAppIsRunning.doNotDelete"), "");
RunRestOfCode();
}
protected override void OnStop()
{
File.Delete(Path.Combine(Path.GetTempPath(), "MyAppIsRunning.doNotDelete"));
}
//...
}
This could easily have the file swapped out with a registry entry or a record in a database.

You can subscribe to below event which will fire no matter in which thread the exception occurs..
AppDomain.CurrentDomain.UnhandledException
Sample implementation
AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
// log the exception ...
}

Web service and global parameter

I start building a new web service for my app and i want to make a global int for example that every time someone call this web service this int will increase in one.
this is what i create in visual studio:
public partial class Form : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
}
and i try to put static int in the class but it not work.

Put your variable in Application state.
Note you need to make it thread safe.
from http://msdn.microsoft.com/en-us/library/94xkskdf(VS.80).aspx
Application.Lock();
Application["PageRequestCount"] =
((int)Application["PageRequestCount"])+1;
Application.UnLock();

WCF client in ASP.net Page

Can anyone advise of a good pattern for using a WCF Service from an ASP.net Page? It seems that if the lifetime of the Client(:ServiceModel.ClientBase) is not properly controlled that we get PipeException thrown. It currently exists as a field of the Page class, but is being reinstantiated upon each page request without being cleaned up (the .Close method).
I suspect this question could be rephrased "Managing limited resources in an ASP.net page", and is probably more related to the lifecycle of an ASP.net page. I'm new to ASP.net, so my understanding of this is a little thin.
TIA.
EDIT: Some code (there's not much to it!)
public partial class Default : Page
{
//The WCF client... obviously, instantiating it here is bad,
//but where to instantiate, and where to close?
private readonly SearchClient client = new SearchClient();
protected void Page_Load(object sender, EventArgs e)
{
2nd Edit: Would the following be better?
public partial class Default : Page
{
private SearchClient client;
protected void Page_Unload(object sender, EventArgs e)
{
try
{
client.Close();
}
catch
{
//gobbled
}
}
protected void Page_Load(object sender, EventArgs e)
{
client= new SearchClient();
//.....

I agree with Michael, abstract it out into another layer if possible.
However, if you are going to call it from your aspx page, I would just create a separate method to call it, return its results and cleanup. Keeps the code clean by having it all in one place. Just remember to dispose in your finally block, and that the wcf proxy will have to be cast to IDisposable in order to dispose.
for instance:
void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack)
{
RemoteCall();
}
}
void RemoteCall()
{
var client = new SearchClient();
try
{
var results = client.Search(params);
clients.Close();
}
catch(CommunicationException cex)
{
//handle
}
catch(Exception ex)
{
//handle
}
finally
{
((IDisposable)client).Dispose();
}
}

In general, you shouldn't call external services directly from your presentation tier. It creates two problems: first, performance (pooling, scaling, etc), and second, it creates a security risk if you need to authenticate (authentication code in your DMZ is bad.
Even if you don't have an application tier, you should consider refactoring your service call to a private service in your presentation tier. This will allow you to decouple the service's lifecycle from the page's lifecycle (which is problematic as you have stated).