RtwIdleDll Control

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Introduction

The 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 (like they have done in Yahoo! Messenger, when there is no activity for a certain amount of time the status of the user is shown as idle). This has many other applications as well. The Application idle time (not the system idle time) can be found easily by resetting a timer on every keyboard or mouse event, but in most cases, it is not adequate for our purposes. Unfortunately, the .NET framework class libraries don't provide much support for getting the system idle time directly.

To do this, there are several ways. One way is by hooking into the mouse and keyboard events of the OS. But I believe the easiest way is by using the GetLastInputInfo() Win32 API. I tried using this in C# without success. So, I decided to write a UserControl in C++ that can be used easily in C# or other languages.

DLL Description

The core of the DLL is the two methods GetLastInputTime() and GetIdleTime(). They use the functions GetLastInputInfo() and GetTickCount() defined in windows.h to get the time from system startup to the last user input and the total time passed since system startup, respectively. Please refer the MSDN documentation for more info on GetLastInputInfo() and GetTickCount().

//returns the time from system startup to last input in milliseconds
DWORD RtwIdleDll::RtwIdleDllControl::GetLastInputTime(void)
{
    LASTINPUTINFO lastInput;
    lastInput.cbSize = sizeof(LASTINPUTINFO);

    BOOL success = GetLastInputInfo(&lastInput);

    if(!success)
    {
        DWORD err=GetLastError();
        // report error, throw exception, etc
    }

    DWORD lastInputTime = lastInput.dwTime;
    return lastInputTime;
}

//returns the time since the last input in milliseconds
DWORD RtwIdleDll::RtwIdleDllControl::GetIdleTime(void)
{
    DWORD totalTime = GetTickCount();
    //gets the time from system startup to now in milliseconds

    DWORD lastInputTime = GetLastInputTime();
    
    DWORD idleTime = totalTime - lastInputTime;

    return idleTime;
}

The following section lists the properties, methods and events exposed by the DLL:

Properties

• IdleTriggerTime (get/set) - The time to wait (in milliseconds) before the first Idle and IdleStart events are fired.
• IsIdle (get) - Is true when idle, otherwise false.

Methods

• ShowAbout() - Shows the About box.

Events

• IdleStart - Fired one time when the idle trigger time is passed.
• Idle - Fired continuously when idle.
• IdleStop - Fired when idle state ends (keyboard or mouse input received).

Limitations

The events are not asynchronous, therefore, using code that would delay the client event handler methods from returning (like modal dialogs or message boxes) inside the event handler methods will sometimes cause unexpected behavior.

Using the DLL

The DLL must be added to another project through the ToolBox. If you are using Visual Studio .NET, right click on the ToolBox and select "Add/Remove Items..." from the popup menu and select the DLL from its location. After that, it will appear in your ToolBox. Then it can be drag'n dropped to any container at design time. After setting the properties and events, it's ready for use.