How to use PInvoke in Silverlight 5

• Download demo - 3.41 MB

Introduction

You might have noticed that the Silverlight 5 (Release Candidate) is out. One of the new features included in the RC is the ability to call P/Invoke. In this short demo, we will write a Silverlight 5 application that uses the feature.

Tools needed:

• Visual Studio 2010 SP1 or Visual Web Developer Express 2010 SP1 is required to develop a Silverlight 5 RC application.
• After you have installed VS2010 SP1 or Visual Web Developer Express 2010 SP1, you will need to download and install the Silverlight 5 (Release Candidate) Tools for Visual Studio 2010 SP1.

Getting Started

Go ahead and open Visual Studio 2010 SP1 and select File->New Project, then Silverlight Application.

By default, we have a new option called “Silverlight 5” selected as the Silverlight version. Let’s go ahead and leave it at that. You also have the ability to select Silverlight 3 or 4 from this drop-down.

Let’s go ahead and right click on our project and select Properties.

Put a check in “Enable running application out of the browser”.

Now go ahead and put a check in “Require elevated trust when running outside the browser”.

Switch back over to MainPage.xaml and add in the following code:

<Grid x:Name="LayoutRoot" Background="White">
    <Button Height="23" HorizontalAlignment="Left" Margin="169,132,0,0" 
       VerticalAlignment="Top" Width="75" x:Name="btnclick" 
       Content="click" Click="click_Click" />
</Grid>

This will simply put a no thrills button on the page that the user can press to call the P/Invoke code we will add shortly.

Let’s go ahead and add a new class to the project.

Let’s call it PlatformInvokeTest.cs and add the following code (Note: If you are having a problem getting it to work, then use my solution at the bottom of the post):

using System;
using System.Runtime.InteropServices;
 
namespace SilverlightApplication26
{
    public class PlatformInvokeTest
    {
        [DllImport("kernel32.dll")]
        public static extern bool Beep(int frequency, int duration);
 
    
        public static void PlaySound()
        {
            Random random = new Random();
            for (int i = 0; i < 50; i++)
            {
                Beep(random.Next(10000), 100);
            }
        }
    }
}

Let’s switch back over to MainPage.xaml.cs and add the following code:

using System.Windows;
using System.Windows.Controls;
 
namespace SilverlightApplication26
{
 
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }
 
        private void click_Click(object sender, RoutedEventArgs e)
        {
            PlatformInvokeTest.PlaySound();
        }
    }
}

Now when the user fires up this project, the application will go out of browser and the computer will beep multiple times in a different frequency each time.

You can also get this same functionality in-browser by going back to the Properties page and selecting “Require elevated trust when running in-browser”.

The only thing to note is that the .aspx page is no longer set to the default in your web project so you will need to do a “View in Browser” on your .aspx page in order to test.

Conclusion

As you can see, it is very easy to use P/Invoke in a Silverlight 5 application. This sample was pretty simple but imagine the possibilities such as detecting when a USB key is inserted into a PC and copying files onto it through a Silverlight 5 application. Pretty cool stuff!

If you want the source code to this application and other Silverlight 5 demos, then be sure to check out Michael’s “Mega Collection of #Silverlight 5" Demos.

Resources

Other Silverlight 5 resources by me are listed below:

• My webinar on “Getting started with the Silverlight 5 Beta”.
• Getting Started with the Silverlight 5 RC
• Getting Started with the Silverlight 5 Beta!
• Game Changing Features in the Silverlight 5 Beta (Part 1)
• Game Changing Features in the Silverlight 5 Beta (Part 2)
• Game Changing Features in the Silverlight 5 Beta (Part 3)