We Keep Coding

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;

Android Things with Xamarin Issue with IGpioCallback

I'm just starting with Android Things with Xamarin, and I've already successfully turned on a LED, but I'm having trouble to detect a push button input.
I think the problem is the "RegisterGpioCallback" in the code below, but I'm not sure and really don't know how to fix it. Can somebody help me?? This is the code I'm using:
public class BlinkActivity : Activity
{
private IGpio gpio;
private IGpio button;
private IGpioCallback mButtonCallback;
protected override void OnCreate(Bundle savedInstanceState)
{
this.mButtonCallback = mButtonCallback;
PeripheralManager peripheralManager = PeripheralManager.Instance;
gpio = peripheralManager.OpenGpio("BCM17");
gpio.SetDirection(Gpio.DirectionOutInitiallyLow);
gpio.Value = false;
button = peripheralManager.OpenGpio("BCM4");
button.SetDirection(Gpio.DirectionIn);
button.SetEdgeTriggerType(Gpio.EdgeNone);
button.RegisterGpioCallback(new Handler(), mButtonCallback);
base.OnCreate(savedInstanceState);
Task.Run(() =>
{
if (mButtonCallback.OnGpioEdge(button) == true)
{
gpio.Value = !gpio.Value;
}
});
}
}

You need to actually implement the IGpioCallback interface so the com.google.android.things.pio library can make a "call back" into your application when the value of the GPIO changes.
Assign the RegisterGpioCallback to the actual object instance that has implemented the interface, in the following example, that will be on the Activity.
public class BlinkActivity : Activity, IGpioCallback
{
~~~~
button.RegisterGpioCallback(new Handler(), this);
~~~~
// remove the Task.Run block
public OnGpioEdge(Gpio gpio)
{
Log.Debug("SO", gpio.Value.ToString());
}
~~~~
}

I had some issues following this in Maui. I'd created an IGPIO interface in the shared code, and then a platform-specific GPIO class inside the Android platform code. The code would run, but then crash when it got to the Registration of the callback. The error said I had to pass a Java.Lang.Object or Java.Lang.Throwable as argument 2 to com.google.android.things.pio.impl.GpioImpl.registerGpioCallback(android.os.Handler, com.google.android.things.pio.GpioCallback).
I tried using each of these as the base class for my GPIO class, but then the app wouldn't build. When I'd autogenerated the IGpioCallback interface implementation in the class it had created a dispose method and a Handle property along with the OnGpioEdge callback method. Removing these allowed the app to work properly. so my class definition ended up looking something like this for the registration and event:
public class GPIO : Java.Lang.Throwable, IGPIO, IGpioCallback
{
public event EventHandler OnButtonEdge;
IGpio ButtonPin;
public void registerPinForEdgeDetection(string pinName)
{
using (var peripheralManager = PeripheralManager.Instance)
{
ButtonPin = peripheralManager?.OpenGpio(pinName);
ButtonPin.SetDirection(Gpio.DirectionIn);
ButtonPin.SetEdgeTriggerType(Gpio.EdgeBoth);
ButtonPin.RegisterGpioCallback(new Android.OS.Handler(), this);
}
}
public bool OnGpioEdge(IGpio gpio)
{
OnButtonEdge?.Invoke(ButtonPin, EventArgs.Empty);
return true;
}
}

Alert Dialog in ViewModel - MVVMCross

In the ViewModel, I have Save method where I check isValid property.
If isValid is false, then I want to display an error message.
Since AlertDialog is platform specific, I wonder how do you handle that situation in the ViewModel?
public void Save()
{
if (isValid)
{
OnExit(this, null);
}
else
{
//issue an alert dialog here
}
}
Update
I have used the following plugin and added the following line of code as follows, but it throws an error.
else
{
Mvx.Resolve<IUserInteraction>().Alert("it is not valid");
}
Update 2
Chance.MvvmCross.Plugins.UserInteraction is a namespace but it is used as a type error.
Update 3
I have added Acr.UserDialogs plugin and called as follows, but I have got the same error.
Mvx.Resolve<IUserDialogs>().Alert("it is not valid");

Using ACR User Dialogs is the simplest approach.
In your App.cs (Core/PCL) you will need to register the interface:
public class App : MvxApplication
{
public override void Initialize()
{
// Example Other registrations
CreatableTypes()
.EndingWith("Service")
.AsInterfaces()
.RegisterAsLazySingleton();
Mvx.RegisterSingleton<IUserDialogs>(() => UserDialogs.Instance);
}
}
Then you can call your alert form your ViewModel.
Mvx.Resolve<IUserDialogs>().Alert("it is not valid");
Note for Android Platform support
Then if you are supporting Android you will need to initialize UserDialog with an instance of the activity context. This will have to be done in each activity that you will be making use of UserDialogs or if you have a shared base activity you can do it there.
[Activity]
public class MainActivity : MvxActivity
{
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
SetContentView(Resource.Layout.activity_main);
// Initialize Acr UserDialogs
UserDialogs.Init(this);
}
}
Alternatively
You can follow the Mvvmcross document on using platform specific implementations of an interface if you need a more custom modal implementation.

This is how I handle the Alert messages in the viewmodel. Try this.
await App.Current.MainPage.DisplayAlert("Active subscription required", "You do not have an active subscription for Part 2 exams", "OK");

There is an existing MvvmCross plugin called User Interaction that allows displaying alerts and collecting inputs from ViewModels.
From the author BrianChance:
Really simple, easy, beautiful ways to show a message box or to collect user input from your ViewModels
Check it out here and NuGet Link Here.
To install the plugin, make sure you override LoadPlugins in your SetUp Class on iOS and Android (and windows phone) like so:
public override void LoadPlugins(MvvmCross.Platform.Plugins.IMvxPluginManager pluginManager)
{
base.LoadPlugins(pluginManager);
pluginManager.EnsurePluginLoaded<Chance.MvvmCross.Plugins.UserInteraction>();
}

My approach is that i use an event for this scenario. My base class for my view models has a EventHandler OnUserNotification, where the views can kinda subscribe to. The UserNotificationType is just an enum and i let the view kinda decide how it reacts to the situation.
The property:
public EventHandler<UserNotificationType> OnUserNotification { get; set; }
The call:
if (OnUserNotification != null)
{
OnUserNotification.Invoke(this, UserNotificationType.ENetworkError);
}
In the view:
private void onUserNotification(object sender, UserNotificationType userNotificationType)
{
// Do Something like showing a Snackbar, AlertDialog, etc...
}
Of course you can make the eventtype more complex if needed.
Didnt try the plugin which got suggested by wishmaster though, so that might be a smoother implementation?

Use Acr.UserDialogs. There is a great examples on github
You can grab it on nuget
It works well with dependency injection or a static singleton UserDialogs.Instance

Passing a StorageFile to OnNavigatedTo in a C# WinRT app

In my C# WinRT app, I would like to pass a StorageFile to a new navigation page inside a frame so that the page can open the document and put the file's contents into a RichEditBox. I've tried to add an optional parameter to OnNavigatedTo with a StorageFile, but it causes the app to crash.
I tried to make it so that I can navigate to the page like this from another page that contains a frame:
RootFrame.Navigate(typeof(Editor), file);
And launch the framed page like so:
protected override async void OnNavigatedTo(Windows.UI.Xaml.Navigation.NavigationEventArgs e, Windows.Storage.StorageFile file)
{
if (file)
{
try
{
EditorBox.Document.SetText(Windows.UI.Text.TextSetOptions.None, await Windows.Storage.FileIO.ReadTextAsync(file));
}
catch
{
}
}
}
But doing this, I get the following errors:
'TestApp.Page3.OnNavigatedTo(Windows.UI.Xaml.Navigation.NavigationEventArgs, Windows.Storage.StorageFile)' is a new virtual member in sealed class 'TestApp.Page3'
'TestApp.Page3.OnNavigatedTo(Windows.UI.Xaml.Navigation.NavigationEventArgs, Windows.Storage.StorageFile)': no suitable method found to override
Is there any way to do something similar to what I am trying to accomplish?

You can only override existing methods. You can't override what doesn't exist - you'd create something new instead. However Windows wouldn't call a method it doesn't know. So stick with what Windows has to offer:
protected override async void OnNavigatedTo(NavigationEventArgs e)
{
var file = e.Parameter as Windows.Storage.StorageFile;
if (file!=null)
{
...
}
}

C# windows 8 app creating a file

I'm trying to create a file then write to the file and read from it as well... kind of like settings for my app to load every time it loads. Why is this not working for me? I'm running visual studio 2012 and I think when I run the program there the file should be created in the project's folder... my method it's async and void... don't really know what is going on haha
StorageFile sampleFile = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("config.txt", CreationCollisionOption.ReplaceExisting);
How can I create this in the local folder? so every time the program runs no matter in what computer it will create the file and load it when the user close and re-open the program?

Man, great question!
Here's the exact logic to do what you are asking:
public class MyData
{
public string Title { get; set; }
}
public sealed partial class MainPage : Page
{
public MainPage()
{
this.InitializeComponent();
}
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
this.DataContext = await LoadData();
}
protected override void OnNavigatedFrom(NavigationEventArgs e)
{
SaveData(this.DataContext as MyData);
base.OnNavigatedFrom(e);
}
private async Task<MyData> LoadData()
{
var _Data = await StorageHelper.ReadFileAsync<MyData>(
this.GetType().ToString(), StorageHelper.StorageStrategies.Local);
return _Data ?? new MyData() { Title = "Welcome" };
}
private async void SaveData(MyData data)
{
await StorageHelper.WriteFileAsync(
this.GetType().ToString(), data, StorageHelper.StorageStrategies.Local);
}
}
The StorageHelper class can be found here. or on my blog http://jerrynixon.com
Best of luck!

How can I create this in the local folder?
You can't, and anyway you're not supposed to... Windows Store apps run in a sandbox, they have a very restricted access to the file system. Basically, you have access to:
your app's LocalFolder (which is not the installation folder) and RoamingFolder
documents library, pictures library, music library, etc, depending on your app's capabilities (declared in the app manifest)
files selected by the user using a file picker
And I think that's about it... You can also access the files in the installation folder (Package.Current.InstallationFolder), but only for reading.