PowerMode, change and status in .NET

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Introduction

This articles explains how to make an application aware of the Battery Status when in use on a laptop/tablet.

PowerMode change comes from Intel documentation on devx. The current power status comes from MSDN in a longhorn article.

Background

See Cancellable Thread Pool for why this is here. This is a very raw and ready post as it's just a couple of searches anyway. The only bit of my code really is the constructor which ensures you have results whenever you instantiate the class.

Using the code

Run the application, and then attempt to generate as many PowerChange events as possible. With a modern ACPI capable desktop PC, you will probably be able to generate Suspend and Resume events. Attempting to change the ACLineStatus is not recommended.

With a laptop/tablet, you should be able to generate the full range of events as long as your battery holds some charge.

The MSDN/Intel documentation does not indicate if these power events are also available from servers via UPS. If anyone has a development machine on a UPS, I would be interested to see a trace of the events. (The file is automatically saved when the application shuts down, see frmPowerDemo_Closed().)

Code Features

There are two parts to this code, firstly detecting PowerChange events, and secondly, finding out the current status. To detect a PowerChange, you first need to use the Microsoft.Win32 namespace, and wire in the event.

//At the Top of the file 
using Microsoft.Win32;
    
//In the Constructor or elsewhere
    SystemEvents.PowerModeChanged 
        += new PowerModeChangedEventHandler(SystemEvents_PowerModeChanged);

Next, it's a simple case of declaring your handler in the usual method.

private void SystemEvents_PowerModeChanged(object sender, 
                          PowerModeChangedEventArgs e)
{

The PowerModeChanged event provides the initial information as to why you get the event, e.g., PowerModeChangedEvent.Suspend, .Resume and .StatusChange. However, you will usually require slightly more complex logic, e.g.:

    //Get the current Status
    PowerStatus ps = new PowerStatus();
    switch (e.Mode)
    {
    case PowerModes.Resume:
        if (ps.BatteryFlag & _BatteryStatus.Critical
            != _BatteryStatus.Critical)
        {
            //Start process that will use lots of CPU

The PowerStatus class is used to provide detail to the current state. It will automatically read the current power status when it is constructed, so all you need to do is read the values off. Of most value are the BatteryFlag and ACLineStatus fields. Both of these are enumerated to provide useful information, although the BatteryFlag is a bitmapped field.

Points of Interest

This code can be used in combination with Threading to provide applications that will throttle back the CPU usage as power becomes critical.

History

v0.1a 13^th Sept 2004. First release.