Develop Reference

Xamarin ContentObserver

trying to get a content observer to work in Xamarin Android.
It's not currently being executed when an event happens.
I tried converting from a java example and fixed it up for c#
I know there is not code to implement the event mod yet, trying to see it get caught first then will add the code.
This is the observer:
using System;
using Android.Database;
using Android.OS;
using Android.Content;
namespace FileTest
{
public class MyObserver : ContentObserver
{
private readonly Android.Net.Uri _uri;
public MyObserver(Android.Net.Uri uri): base(null)
{
_uri = uri;
}
public override void OnChange(bool selfChange) {
this.OnChange (selfChange, null);
Console.WriteLine ("change that I caught " );
}
// public override void OnChange(bool selfChange, Uri uri) {
//
// Console.WriteLine ("change that I caught " );
//
//}
}
}
this is the call:
ContentObserver observer = new MyObserver(Android.Net.Uri.Parse("content://com.Test/databases/Data.db"));
// TODO Auto-generated method stub
var a = Android.Net.Uri.Parse ("content://com.Test/databases/Data.db");
ContentResolver.RegisterContentObserver(a, false, observer);

The calling thread cannot access this object because a different thread owns it (in v4.5)

I am aware that there are plenty questions have been already asked on this. But the solutions provided about delegates is not what I am getting to work with my code because I am working on 4.5 version and looks like the Dispatcher methods have slightly changed. Added to that, I am touching dotnet nearly after a decade and c# for the first time.
What I am actually tying to do in my WPF project is to append text of the textbox inside the main window to display the status/log. This is inside the singleton class called Logger The main static function of this class is log() which accepts a string which needs to be added to the text box with one simple line
txt.AppendText(msg);
After doing some research I changed it to
Dispatcher.CurrentDispatcher.Invoke(() =>
{
txt.AppendText(msg);
});
But I still get the same error. What is going wrong here? Is there anything else to do? Because I am calling this Logger.log() from FileSystemEventHandler insider another singleton class.
private void somethingChanged(object sender, FileSystemEventArgs e)
{
Logger.log("File: " + e.FullPath + " " + e.ChangeType);
}
Below is my Logger class
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Controls;
using System.Windows.Threading;
using System.Threading;
namespace httpclientui.comps
{
class Logger
{
private static TextBox txt;
private Logger() { }
public static void setup(TextBox t){
txt = t;
}
public static void clear()
{
if (txt == null)
{
return;
}
txt.Clear();
}
public static void log(String msg, bool addNewLineChar = true)
{
if (txt == null)
{
return;
}
Dispatcher.CurrentDispatcher.Invoke(() => {
txt.AppendText(msg);
});
}
}
}
This is my main window with only one textbox control called txtMessage.
public partial class MainWindow : Window
{
private String folderToWatch;
public MainWindow()
{
InitializeComponent();
initialize();
}
private void initialize()
{
Logger.setup(txtMessage);
Logger.clear();
Logger.log("Launched");
folderToWatch = "E:\\folder\\subfolder";
Watcher.Instance.setup(folderToWatch);
Watcher.Instance.start();
}
}
}
Below is my Watcher class which has FileSystemWatcher object to keep watching one of the folder and whenever something happens inside that folder like adding/deleting files and renaming the files will needs to be logged inside that textbox.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace httpclientui.comps
{
class Watcher
{
private String path;
//https://msdn.microsoft.com/en-us/library/system.io.filesystemwatcher(v=vs.110).aspx
private FileSystemWatcher dog;
private static Watcher instance;
private Watcher()
{
//dog = new FileSystemWatcher()
}
public static Watcher Instance
{
get
{
if (instance == null)
{
instance = new Watcher();
}
return instance;
}
}
public void setup(String folderPath)
{
path = folderPath;
dog = new FileSystemWatcher(folderPath);
Logger.log("setting up to watch folder: " + folderPath);
dog.Changed += new FileSystemEventHandler(somethingChanged);
dog.Created += new FileSystemEventHandler(somethingChanged);
dog.Deleted += new FileSystemEventHandler(somethingChanged);
dog.Renamed += new RenamedEventHandler(somethingRenamed);
}
public void start()
{
Logger.log("starting to watch folder");
dog.EnableRaisingEvents = true;
}
public void pause()
{
dog.EnableRaisingEvents = false;
}
public void stop()
{
dog.EnableRaisingEvents = false;
}
private void somethingChanged(object sender, FileSystemEventArgs e)
{
Logger.log("File: " + e.FullPath + " " + e.ChangeType);
}
private void somethingRenamed(object sender, RenamedEventArgs e)
{
Logger.log("File: " + e.OldFullPath + " renamed to " + e.FullPath);
}
}
}

At first glance, it looks like you are not marshalling the Clear() method call to the Dispatcher. That's what is likely throwing the exception- all access to DispatcherObjects (which includes all Controls) must be done by the Dispatcher thread.
Also, you want to use Application.Current.Dispatcher, not Dispatcher.CurrentDispatcher. The latter just spins up a new Dispatcher on the current (background) thread, which is not what you want.

Skype API Message output

How can I receive and output message from Skype to my application (textbox1.Text)?
I was looking for it in skype4com documentation but didn't find anything.

To listen for chat messages you can do something like this:
//First make a reference to skype4com, probably in here: C:\Program Files (x86)\Common Files\Skype
//Then use the following code:
using System;
using System.Windows.Forms;
using SKYPE4COMLib;
namespace Skype
{
public partial class Form1 : Form
{
private SKYPE4COMLib.Skype skype;
public Form1()
{
InitializeComponent();
skype = new SKYPE4COMLib.Skype();
skype.Attach(7, false);
skype.MessageStatus += new _ISkypeEvents_MessageStatusEventHandler(skype_MessageStatus);
}
private void skype_MessageStatus(ChatMessage msg, TChatMessageStatus status)
{
string message = msg.Sender + ": " + msg.Body;
listBox1.Items.Add(message);
}
}
}

Windows form loads then quits

I'm creating a checkout system for a supermarket. It consists of a checkout, server and MIS program an operates WCF services between them. The problem I have is that the checkout program, which is a windows form, does a few neccessaries in it's application_load method and then just quits.
Here's the code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using CheckoutLibrary;
using Checkout.ServerLibraryService;
using Checkout.MarketService;
namespace Checkout
{
public partial class theForm : Form
{
private static int checkoutID = 3;
private Product[] allProducts;
public theForm()
{
InitializeComponent();
}
private void theForm_Load(object sender, EventArgs e)
{
// First cache all products
SupermarketServiceSoapClient marketService = new SupermarketServiceSoapClient();
allProducts = marketService.GetAllProducts();
// Load the service provided by the server
ServiceClient serverService = new ServiceClient();
// Load the event handlers for the bar code scanner
BarcodeScanner scanner = new BarcodeScanner();
scanner.ItemScanned += new BarcodeScanner.ItemScannedHandler(scanner_ItemScanned);
scanner.AllItemsScanned += new BarcodeScanner.AllItemsScannedHandler(scanner_AllItemsScanned);
scanner.Start(checkoutID);
}
void scanner_AllItemsScanned(EventArgs args)
{
throw new NotImplementedException();
}
void scanner_ItemScanned(ScanEventArgs args)
{
itemTextBox.Text = "Scanned " + GetItemName(args.Barcode);
}
private void scanItemButton_Click(object sender, EventArgs e)
{
scanner_ItemScanned(new ScanEventArgs(GetRandBarcode()));
}
// A barcode -> product name look up method
public string GetItemName(int barcode)
{
return allProducts[barcode].Description + " # " + allProducts[barcode].Price;
}
// Method to grab a random barcode for simulation
private int GetRandBarcode()
{
Random rand = new Random();
return rand.Next(0,500);
}
}
}
And program.cs:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
namespace Checkout
{
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new theForm());
}
}
}
Thanks for any insight.

In WinForms, if your form_load throws an exception, it quits without displaying anything. Annoying, but I'm guessing that's the problem.
You can try a try/catch, or you can hit CTRL+ALT+E and check the Thrown Column for Common Language Runtime Exceptions to see the error.
UPDATE:
Based on comments, here's a sample way to execute something on another thread.
ThreadStart ts = new ThreadStart(() => {
try {
scanner.Start(checkoutID);
} catch {
// Log error
}
});
Thread t = new Thread(ts);
t.Start();

Does WqlEventQuery contain a constructor with 1 argument?

I am trying to create a simple service in C# using VS2008 that creates a text file when the computer goes into sleep mode. My current code throws out the following error:
'SleepNotifierService.WqlEventQuery' does not contain a constructor that takes '1' arguments
Now I looked in the Object browser, and it looks like it does take in one argument. This is what the browser had to say:
public WqlEventQuery(string queryOrEventClassName)
Here is my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Linq;
using System.ServiceProcess;
using System.Text;
using System.Management;
using System.IO;
namespace SleepNotifierService
{
public class WqlEventQuery : EventQuery { }
public partial class Service1 : ServiceBase
{
ManagementEventWatcher _watcher;
public Service1()
{
InitializeComponent();
}
protected override void OnStart(string[] args)
{
WqlEventQuery query = new WqlEventQuery("Win32_PowerManagementEvent");
_watcher = new ManagementEventWatcher(query);
_watcher.EventArrived += new EventArrivedEventHandler(watcher_EventArrived);
_watcher.Start();
}
protected override void OnStop()
{
_watcher.Stop();
}
void watcher_EventArrived(object sender, EventArrivedEventArgs e)
{
try
{
int eventType = Convert.ToInt32(e.NewEvent.Properties["EventType"].Value);
switch (eventType)
{
case 4:
Sleep();
break;
case 7:
Resume();
break;
}
}
catch (Exception ex)
{
//Log(ex.Message);
}
}
public void Sleep()
{
StreamWriter SW;
SW = File.CreateText("c:\\MyTextFile.txt");
SW.WriteLine("Sleep mode initiated");
SW.Close();
}
public void Resume()
{
}
}
}
Am I interpreting that object browser wrong? I'm new to creating services and C#/.NET in general so it might be something trivial.
Appreciate any help,
Tomek

You're using wrong WqlEventQuery. There's one defined in System.Management and it indeed has a one-argument constructor, but there's also your custom WqlEventQuery class.
If you want to use .NET BCL's class, you'll have to fully qualify it:
var query = new System.Management.WqlEventQuery("Win32_PowerManagementEvent");
or even prefix it with global keyword:
var query = new global::System.Management.WqlEventQuery("Win32_PowerManagementEvent");