In my early WPF days I noticed the magic that having two different controls bound to the Same ObservableCollection meant that when I selected an item in one control, the same item got selected in the other.... which i I didn't want.

CollectionViewSource To the rescue

<Window.Resources>
<local:MyData x:Key="MyData"/>  
    <CollectionViewSource x:Key="AllData" Source="{StaticResource MyData}"/>  
    <CollectionViewSource x:Key="SearchData" Source="{StaticResource MyData}" Filter="MySearch"/>  
</Window.Resources> 
 
<ListBox ItemsSource="{Binding Source={StaticResource AllData}}"/>  
<ListBox ItemsSource="{Binding Source={StaticResource SearchData}}"/>

"object x" is a shorthand for "System.Object x".
This declares the variable x to have the type System.Object, this is strongly typed.
And since C# provides autoboxing, you can assign anything you want to this variable.

"var x = E" declares a variable x to be of the type of the expression E.
The E is required, not optional. This is a strongly typed declaration, and you can only assign values whose type is typeof(E) to it.

"dynamic x" declares the variable x to have dynamic semantics.
This means that the C# compiler will generate code that will allow dynamic invocations on x.
The actual meaning of "x.M" is deferred until runtime and will depend on the semantics of the IDynamicObject implementation

Recently I've noticed that the country has gone iPhone mad and I'm starting to buy into it myself... my blackberry days may be numbered as the only distinct advantage I see is that bandwidth is not used retrieving emails... but nowadays bandwidth is not so much as issue,, e.g. you get 2gb a month on a vodafone contract

I've had a bit of a play around with Objective-C, interesting but .NET is my forte so I was delighted to see that it was possible (kinda0 to write code in c# for the iPhone platform.

The success of .NET platform from MS on multiple systems came when the Mono project became real. This open-source framework (cross-platform) brought the speed of C# development to Linux and OSX platforms. And now it will take us further.

As we all know, Apple has a highly strict inclusion policy for third-party runtime environments, which makes impossible to distribute apps that use this technology, like .NET and Java. So how can I be talking about .NET on the iPhone?

Because of a process called Static Compilation. Mono had already created a way to generate native code from common intermediate language (CIL) produced by .NET in native code in the past (AOT Ahead-OfTime compilation), with the intention of helping to reduce the speed of the initialization process and increase the process sharing among multiple processes. However, to keep the portability among different machines, a small piece of code was still in JIT (just-in-time) compilation – this method is the key to virtual machine systems that generate intermediate code which is converted to native code during execution.

So this process generates the final result in native code BEFORE the executing time, and this decreases also the size of the final app (since framework must go with the app), which does not need to load the codes to execute JIT and interpret CIL – even though it still adds approximately 6Mb from mono framework itself in the app’s final size.

There are also a few other tricks and Mono features that developers can use to reduce the size of Mono executables and assemblies for deployment in mobile environments. You can use the Mono linker to shrink the library size, you can omit the JIT and code generation engines from the executables, and you can strip out CIL instructions from the assemblies.

Static compilation makes it possible to build Apple-approved iPhone applications with Mono, but it comes with some limitations. Generics and dynamically-generated code are currently not supported when AOT compilation is used.

There are a lot of hoops to jump through right now to set up iPhone cross-compilation for Mono, but de Icaza (Novell's lead mono developer) says that developers who want to start now can use Unity, a third-party commercial programming framework for 3D game development that is built on Mono. Unity supports several platforms, including the iPhone and the Wii, and comes with its own built-in Mono cross-compilation environment.

Nowadays, thank to Unity 3D, there are over 40 apps (mostly games) on App Store that were written in C# and that carry mono framework inside. Wouldn’t it be great if Apple included that in the firmware? Imagine that if we have these 40 apps installed, it’s 40 times the same framework consuming space and no need for that. But that’s asking too much, right?

Here's how to ensure that databinding happens when the value of a textbox changes. (as apposed to loosing forcus for example)

[code:c#]
<TextBox Text="{Binding Interval, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"  />
[/code]

Just a sample that may catch you eye as unusual..

[code:c#]

 class WorkItem
{
    public WaitCallback Callback;
    public object State;
    public ExecutionContext Context;

    private static ContextCallback _contextCallback = s =>
    {
        var item = s as WorkItem;
        item.Callback(item.State);
    };

    public void Execute()
    {
        if (Context != null)
            ExecutionContext.Run(Context, _contextCallback, this);
        else
            Callback(State);

    }
}

[/code]

 but here's the same code using anon delegates

[code:c#]

class WorkItem
{
    public WaitCallback Callback;
    public object State;
    public ExecutionContext Context;

    private static ContextCallback _contextCallback = delegate(object s)
    {
        var item = s as WorkItem;
        item.Callback(item.State);
    };

    public void Execute()
    {
        if (Context != null)
            ExecutionContext.Run(Context, _contextCallback, this);
        else
            Callback(State);

    }
}

[/code]

·      Authentication

·      Access control

·      Auditing

Authentication.

One of the critical requirements of any LOB application ia authentication; before the user can use any function he will authenticate by giving a user id and password.

In ASP.NET web application, thi can easily be done by taking advantage of the membership provider and the server-side ASP.NET login controls. In Silverlight, there are two ways to enforce authentication: authentication outside and authentication inside.

Authentication outside is very straightforward and is similar to ASP.NET applications, with this approach, authentication happens in anASP.NET based web page before the Silverlight application is displayed. The authentication context can be transferred into the Silverlight application through the InitParams parameter before a Silverlight application is loaded. The other approach is to use a webservice.

When you wish to know if you are on the UI thread and you've no access to any UIElement how do you do it?

[code:c#]

static bool IsUiThread()
{
    return Deployment.Current.Dispatcher.CheckAssess();
}

[/code]

Here's a bit of code that i'm using in an application to give this result (Checked GroupBox)

[code:c#]

<GroupBox Grid.Row="3" Grid.Column="1" BorderBrush="Black" Margin="0,0,116,0">
<GroupBox.Header>
    <CheckBox x:Name="cbValidity" IsChecked="{Binding Path=HasValidity}" >Validity</CheckBox>
</GroupBox.Header>

<StackPanel>
    <StackPanel.Style>
        <Style>
            <Style.Triggers>
                <DataTrigger Binding ="{Binding ElementName=cbValidity, Path=IsChecked}" Value="false">
                    <Setter Property="Button.IsEnabled" Value="false"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </StackPanel.Style>
    <TextBlock Margin="10,10,0,0" Text="This job is valid from" />
    <wfi:WindowsFormsHost x:Name="propertiesCtrlHost" SnapsToDevicePixels="True" Background="Transparent" Height="22" Margin="10" Width="200" HorizontalAlignment="Left">
        <wf:DateTimePicker x:Name="dtpFrom" Format="Custom" CustomFormat="dd MMMM yyyy  HH:mm" ValueChanged="dtpFrom_ValueChanged" />
    </wfi:WindowsFormsHost>

    <TextBlock Margin="10,10,0,0" Text="This job is valid to" />
    <wfi:WindowsFormsHost SnapsToDevicePixels="True" Background="Transparent" Height="22" Margin="10" Width="200" HorizontalAlignment="Left">
        <wf:DateTimePicker x:Name="dtpTo" Format="Custom" CustomFormat="dd MMMM yyyy  HH:mm" ValueChanged="dtpTo_ValueChanged" />
    </wfi:WindowsFormsHost>
</StackPanel>
</GroupBox>

[/code]

Here's one way to do validation in silverlight.

This is a pretty straight method using exceptions (if you're from the camp that allows exceptions in your Data objects )

[code:c#]

public string Name
{ 
 get 
 {
     return _name; 
 } 
 set 
 {   
  if ( value.Length >= 10 )
    throw new ArgumentException( "Name is too long" );   
  _name = value;
 }
}

<TextBox x:Name="name"
  <TextBox.Text>
   <Binding Path="name"
     NotifyOnValidationError="True"
      ValidatesOnExceptions="True" />  
 </TextBox.Text>
</TextBox>

[/code]

Requirment:

Nothwind Sql Database

Advantages of Linq to SQL

While everything with Linq to Sql ca be done with Ado.Net, there are a few advantages

• Less code: you don't need to write ADO.NET code for querying the database. You can use a tool to generate the data classes you need.
• Flexible querying capabilities: Rather than struggle with SQL, you can use the LINQ querying model. Ultimately, you'llbe able to use one consistent model (LINQ expressions) to access many different types of data, from databases to XML.
• Change tracking and batch updates: This is the most important one for me, (because I already have ado.net tools and i don't mindwriting sql) You can change multiple details about the data yo've queried and commit a batch update. 

Add a new linq to sql item to your project 

 Sample usage

[code:c#]

class Program
{
    static void Main(string[] args)
    {
        Program prog = new Program();
        prog.ListAllOrderProducts();
        prog.ListAllOrderProductsForCustomer();
        Console.ReadLine();
    }

    private void ListAllOrderProducts()
    {
        CustomerOrdersDataContext dc = new CustomerOrdersDataContext();
        Table<Order> table = dc.GetTable<Order>();
        foreach (var order in table)
        {
            Console.WriteLine(order.Order_Details[0].Product.ProductName);
        }           
    }

    private void ListAllOrderProductsForCustomer(string custId = "ALFKI")
    {
        CustomerOrdersDataContext dc = new CustomerOrdersDataContext();
        var result =
            from order in dc.GetTable<Order>()
            where order.CustomerID == custId
            select order;
                   
        foreach (var x in result)
        {
            Console.WriteLine(x.Order_Details[0].Product.ProductName);
        }
    }
}

[/code]