I’ve been doing some Windows Mobile development with the .NET Compact Framework recently and ran into a scenario where I needed the device to be in “full power” mode at all times with the back-light on. The device is constantly powered, so battery life is not a concern.
The obvious choice is to go into the Brightness and Power control panels and turn off the appropriate settings, but I learned that there is a way to handle this at an application level so the behavior only occurs while the application is running.
Power State
An application can force a specific power state using the SetPowerRequirement method, and release that state using the ReleasePowerRequirement method. Using P/Invoke, these methods look like the following:
1: public enum CEDevicePowerState
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum2" style="color: #606060"> 2:</span> {</pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum3" style="color: #606060"> 3:</span> D0 = 0, <span style="color: #008000">// Full On</span></pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum4" style="color: #606060"> 4:</span> D1, <span style="color: #008000">// Low On</span></pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum5" style="color: #606060"> 5:</span> D2, <span style="color: #008000">// Standby</span></pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum6" style="color: #606060"> 6:</span> D3, <span style="color: #008000">// Sleep</span></pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum7" style="color: #606060"> 7:</span> D4, <span style="color: #008000">// Off</span></pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum8" style="color: #606060"> 8:</span> }</pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum9" style="color: #606060"> 9:</span>  </pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum10" style="color: #606060"> 10:</span> [DllImport(<span style="color: #006080">"coredll.dll"</span>, SetLastError=<span style="color: #0000ff">true</span>)]</pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum11" style="color: #606060"> 11:</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">extern</span> IntPtr SetPowerRequirement(<span style="color: #0000ff">string</span> device, CEDevicePowerState ceDevicePowerState, <span style="color: #0000ff">uint</span> deviceFlags, IntPtr systemState, <span style="color: #0000ff">ulong</span> stateFlags);</pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum12" style="color: #606060"> 12:</span>  </pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum13" style="color: #606060"> 13:</span> [DllImport(<span style="color: #006080">"coredll.dll"</span>, SetLastError=<span style="color: #0000ff">true</span>)]</pre>
<pre style="padding-right: 0px; padding-left: 0px; font-size: 8pt; padding-bottom: 0px; margin: 0em; overflow: visible; width: 100%; color: black; border-top-style: none; line-height: 12pt; padding-top: 0px; font-family: consolas, 'Courier New', courier, monospace; border-right-style: none; border-left-style: none; background-color: #f4f4f4; border-bottom-style: none"><span id="lnum14" style="color: #606060"> 14:</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">extern</span> <span style="color: #0000ff">int</span> ReleasePowerRequirement(IntPtr handle);</pre>
SetPowerRequirement will allow you to set a specific power state on a specific device. In my scenario, I wanted to set the back-light to full power. The name of the back-light on most (not all) Windows Mobile devices appears to be “BKL1:”. So, to set the back-light to full power (the D0 state), you would call the method as follows:
