Getting the user idle time with C#

• Download source - 10.1 Kb

Introduction

System idle time is the time that has passed since the computer has received its last input from the user. It can be used to detect whether the user is idle or not. This feature is present in many instant messaging systems.

Visual Studio 2003 does not provide an explicit way to accomplish this, but I found an alternate method using C# code only.

Using the code

The implemented solution calls functions inside the user32.dll and kernel32.dll files.

To do this, it is necessary:

1. To add a reference to the System.Runtime.InteropServices namespace.
2. To know the name and definition of the function to be called.
3. To create an extern function using C#.
4. To make any additional structure to be used in the called functions.

// Step 1
using System.Runtime.InteropServices;

// Steps 2 and 3
[DllImport("User32.dll")]
private static extern bool 
        GetLastInputInfo(ref LASTINPUTINFO plii);

//Step 4
internal struct LASTINPUTINFO 
{
    public uint cbSize;

    public uint dwTime;
}

When I was trying to make things works, I found an issue with the LASTINPUTINFO structure. I solved the problem by creating a C# struct with the same members as the original function. Note that you need to know the mapping between a Windows data type and the .NET Framework data types. The following table is very useful:

When using a struct as a parameter, you have to initialize it before it is passed to the function:

LASTINPUTINFO lastInPut = new LASTINPUTINFO();
lastInPut.cbSize = (uint)
  System.Runtime.InteropServices.Marshal.SizeOf(lastInPut);

The rest of the code does not contain any trick.

Using the code

The best method to use the code is compiling it in an DLL and using the functions asynchronously using a timer or threads.