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   <TITLE>Prevent the screensaver from running</TITLE>

   <META NAME="Author" CONTENT="Harold Howe">

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<H3>

Prevent the screensaver from running

</H3>



<P>

You can use two techniques to prevent the screensaver from starting. You can respond to

<TT>WM_SYSCOMMAND</TT> messages, or you can call the <TT>SystemParametersInfo</TT> API

function. This FAQ describes both techniques.

</P>

<BR>

<B><TT>SystemParametersInfo</TT>:</B>

<P>

<TT>SystemParametersInfo</TT> allows you to get and set a host of system settings.

Among other things, it allows you to turn off the screensaver. You can also get and set

the screensaver delay time. The code segment below shows a program with two button click

handlers. One button deactivates the screensaver, the other turns it on. The constructor

of the form determines if the screensaver was originally active when the program started

, and what the screensaver delay was set to. As an added bonus, I threw in a function

that sets the screensaver timeout to 30 seconds.

</P>

<pre>

<b>__fastcall</b> TForm1<b>:</b><b>:</b>TForm1<b>(</b>TComponent<b>*</b> Owner<b>)</b>

    <b>:</b> TForm<b>(</b>Owner<b>)</b>

<b>{</b>

    <font color="navy">// Find out if the screensaver was active and what the</font>

    <font color="navy">// screen saver timeout value is.</font>

    BOOL bActive<b>;</b>

    <b>int</b>  nTimeout<b>;</b>

    SystemParametersInfo<b>(</b>SPI_GETSCREENSAVEACTIVE<b>,</b>  <font color="blue">0</font><b>,</b> <b>&</b>bActive<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>

    SystemParametersInfo<b>(</b>SPI_GETSCREENSAVETIMEOUT<b>,</b> <font color="blue">0</font><b>,</b> <b>&</b>nTimeout<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>



    <b>if</b><b>(</b>bActive<b>)</b>

        Label1<b>-></b>Caption <b>=</b> <font color="blue">"Screensaver was active"</font><b>;</b>

    <b>else</b>

        Label1<b>-></b>Caption <b>=</b> <font color="blue">"Screensaver was turned off"</font><b>;</b>



    Label2<b>-></b>Caption <b>=</b> <font color="blue">"Screensaver delay time = "</font> <b>+</b> IntToStr<b>(</b>nTimeout<b>)</b><b>;</b>

<b>}</b>

<font color="navy">//---------------------------------------------------</font>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button1Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    <font color="navy">// Enable the screen saver.</font>

    SystemParametersInfo<b>(</b>SPI_SETSCREENSAVEACTIVE<b>,</b> TRUE<b>,</b> NULL<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>

<b>}</b>

<font color="navy">//---------------------------------------------------</font>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button2Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    <font color="navy">// Disable the screen saver.</font>

    SystemParametersInfo<b>(</b>SPI_SETSCREENSAVEACTIVE<b>,</b> FALSE<b>,</b>NULL<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>

<b>}</b>

<font color="navy">//---------------------------------------------------</font>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button3Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    <font color="navy">// set the screensaver timeout to 30 seconds.</font>

    SystemParametersInfo<b>(</b>SPI_SETSCREENSAVETIMEOUT<b>,</b> <font color="blue">30</font><b>,</b> NULL<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>

<b>}</b>

</pre>

<BR>

<B><TT>WM_SYSCOMMAND</TT></B>

<P>

Before Windows starts the screensaver, it broadcasts a <TT>WM_SYSCOMMAND</TT> message

with <tt>WPARAM</TT> set to <TT>SC_SCREENSAVE</TT>. If any program catches the message and

returns true, the screensaver will not start. Here is a code example that shows how to

prevent the screensaver from running by detecting the <TT>WM_SYSCOMMAND</TT> message.

</P>

<pre>

<font color="navy">//----------------------------------------------</font>

<font color="navy">// class header file</font>

<b>private</b><b>:</b>	    <font color="navy">// User declarations</font>

    <b>void</b> <b>__fastcall</b> WndProc<b>(</b>Messages<b>:</b><b>:</b>TMessage <b>&</b>Message<b>)</b><b>;</b>





<font color="navy">//----------------------------------------------</font>

<font color="navy">// CPP source file</font>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>WndProc<b>(</b>Messages<b>:</b><b>:</b>TMessage <b>&</b>Message<b>)</b>

<b>{</b>

    <b>if</b><b>(</b> <b>(</b>Message<b>.</b>Msg    <b>==</b> WM_SYSCOMMAND<b>)</b> <b>&&</b>

        <b>(</b>Message<b>.</b>WParam <b>==</b> SC_SCREENSAVE<b>)</b>    <b>)</b>

    <b>{</b>

        ShowMessage<b>(</b><font color="blue">"screensaver disabled"</font><b>)</b><b>;</b>

        Message<b>.</b>Result <b>=</b> <b>true</b><b>;</b>

    <b>}</b>

    <b>else</b>

        TForm<b>:</b><b>:</b>WndProc<b>(</b>Message<b>)</b><b>;</b>

<b>}</b>

</pre>

<BR>

<P>

<B>Note:</B> If you deactivate the screensaver with <TT>SytemParametersInfo</TT>, make

sure that you reenable it before your program terminates. The screensaver remains disabled

until somebody activates it again.

</P>

<P>

<B>Note:</B> <TT>SytemParametersInfo</TT> enables the screensaver, but it doesn't

actually execute it.

</P>

<P>

<B>Note:</B> Enabling the screensaver with <TT>SytemParametersInfo</TT> does not guarantee

that the screensaver will run. If the user has turned of the screensaver via control panel,

the OS will not activate the screensaver.

</P>

<P>

<B>Note:</B> Intercepting the <TT>WM_SYSCOMMAND</TT> message is probably more robust than

using <TT>SytemParametersInfo</TT> because another program can call

<TT>SystemParametersInfo</TT> and override any previous settings that you make.

</P>



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