Dynamically loading controls in Silverlight

Recently I found myself wanting to specify at ‘start up’ time which Control loaded by default in a Silverlight application. For those of you that dont know, you can pass initParams into the Silverlight application that are available at Application Start.

An example of this could be like.

<div id="silverlightControlHost">
    <object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%">
      <param name="source" value="ClientBin/EMASolutions.CMS.Plugins.Silverlight.xap"/>
      <param name="onError" value="onSilverlightError" />
      <param name="background" value="white" />
      <param name="minRuntimeVersion" value="3.0.40818.0" />
      <param name="autoUpgrade" value="true" />
      <param name="initParams" value="firstControl=EMASolutions.CMS.Plugins.Silverlight.FolderBrowser" />
      <a href="http://go.microsoft.com/fwlink/?LinkID=149156&v=3.0.40818.0" style="text-decoration:none">
          <img src="http://go.microsoft.com/fwlink/?LinkId=108181" alt="Get Microsoft Silverlight" style="border-style:none"/>
      </a>
    </object>
    <iframe id="_sl_historyFrame" style="visibility:hidden;height:0px;width:0px;border:0px"></iframe>
</div>

The initParams take the following format, key=value,key1=value1. Notice in this example we passover the fully qualified type name of the control to load on Application Start. This is a simple example, in reality the type name would be driven from user actions and would probably be a persisted value rather than a ‘magic string’.

Anyway, we can access our ‘firstControl’ value like so.

private void Application_Startup(object sender, StartupEventArgs e)
{
    if (!NetworkInterface.GetIsNetworkAvailable()) return;
    if (e.InitParams.Any())
    {
        if (e.InitParams["firstControl"] != null)
            LoadControl(
                (Control)
                Activator.CreateInstance(
                    sender.GetType().Assembly.GetType(e.InitParams["firstControl"])));
    }
    else
    {
        LoadControl(
            (Control)
            Activator.CreateInstance(
                sender.GetType().Assembly.GetType("EMASolutions.CMS.Plugins.Silverlight.FolderBrowser")));
    }
    RootVisual = Container;
}

Notice, if the type was not specified, we can load a default control. Again, this is a simple example and the default control could be a persisted value also.

In this example, I am making use of a variable called Container, defined like so.

public static readonly Master Container = new Master();

Master has the following xaml and the default code behind.

<UserControl x:Class="EMASolutions.CMS.Plugins.Silverlight.Master"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    >
    <Grid x:Name="LayoutRoot">

        <Grid.RowDefinitions>
            <RowDefinition Height="30" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>
        
        <Grid Name="TopBar" Grid.Column="0"  Grid.Row="0"></Grid>
        <Grid Name="Main" Grid.Column="0" Grid.Row="1"></Grid>
        
    </Grid>
</UserControl>

All that master does, is give us place holders to load our control into, one called Main and one called TopBar. In the Application_Startup method you will also notice the use of a method called LoadControl. This is what loads controls into our container. It is defined like so.

public static void LoadControl(Control control)
{
    if (Container.Main.Children.Any())
        LastControl = (Control)Container.Main.Children.First();
    Container.Main.Children.Clear();
    Container.TopBar.Children.Add(new TopBar());
    Container.Main.Children.Add(control);
}

We set a LastControl value if there was one, so that we can navigate backwards and then we clear the current controls and add our new control and a TopBar control.

We can also make use of the LoadControl method in other controls. For example, if we have an Authenticate control that logs in a user, we may wish to load another control if authentication failed. We could do this like so.

if (OnFailedAuthentication != null)
{
    OnFailedAuthentication(sender,e);
    App.LoadControl(new Unauthorised());
}

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