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   <TITLE>Minimize all open applications</TITLE>

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

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<H3>

Minimize all open applications

</H3>



<P>

Windows contains a system wide hotkey that allows the user to minimize all programs

with one keystroke. The hotkey is the windows key plus M. One way to minimize all programs

from code is to artificially emulate this hotkey. You could accomplish this by broadcasting a

<TT>WM_HOTKEY</TT> message. However, I decided to seek a different approach for several

reasons. For starters, the hotkey might vary from language to language, and it may be

customizable by the user. Another reason to avoid the <TT>WINDOWS + M</TT> keystroke is that

some machines don't have that wonderful windows key on the keyboard. Does the operating

system still create a system wide hotkey even if the key isn't present? Who knows. Not to

mention the fact that the <TT>WM_HOTKEY</TT> approach probably won't work on windows NT 3.5.

Lastly, who knows how long the <TT>WINDOWS + M</TT> hotkey will be around. If the hotkey

ever goes away, your code would malfunction.

</P>

<P>

I decided to implement a hard-core technique using plain API calls. The process is broken

into two steps. The first step is to tell windows to enumerate the windows on the desktop.

The second step is to write the enumeration callback and design it to minimize each

program.

</P>

<H4>Step 1: Enumerating the desktop windows.</H4>

<P>

The code for the enumeration step is shown below. The <TT>EnumWindows</TT> API function

allows us to enumerate the windows on the desktop. <TT>EnumWindows</TT> takes a function as an

argument. The operating system will call the function that you pass to <TT>EnumWindows</TT>

once for each window on desktop. The <TT>EnumWindows</TT> statement does not return until

the callback has executed for each window.

</P>

<pre>

<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">// determine if minimization animation was originally on</font>

    ANIMATIONINFO info<b>;</b>

    info<b>.</b>cbSize <b>=</b> <b>sizeof</b><b>(</b>info<b>)</b><b>;</b>

    SystemParametersInfo<b>(</b>SPI_GETANIMATION<b>,</b><b>sizeof</b><b>(</b>info<b>)</b><b>,</b><b>&</b>info<b>,</b><font color="blue">0</font><b>)</b><b>;</b>

    <b>bool</b> bAnimationWasOn <b>=</b> info<b>.</b>iMinAnimate<b>;</b>



    <font color="navy">// if animation was on, then turn it off to speed things up</font>

    <b>if</b><b>(</b>bAnimationWasOn<b>)</b>

    <b>{</b>

        info<b>.</b>iMinAnimate <b>=</b> <b>false</b><b>;</b>

        SystemParametersInfo<b>(</b>SPI_SETANIMATION<b>,</b> <b>sizeof</b><b>(</b>info<b>)</b><b>,</b> <b>&</b>info<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>

    <b>}</b>



    <font color="navy">// disable painting of the desktop until we are finished</font>

    LockWindowUpdate<b>(</b>GetDesktopWindow<b>(</b><b>)</b><b>)</b><b>;</b>



    <font color="navy">// enumerate the desktop windows</font>

    EnumWindows<b>(</b><b>(</b>WNDENUMPROC<b>)</b>MinimizeAllWindows<b>,</b> <font color="blue">0</font><b>)</b><b>;</b>



    <font color="navy">// enable desktop painting</font>

    LockWindowUpdate<b>(</b>NULL<b>)</b><b>;</b>



    <font color="navy">// turn the animation back on if it was originally on</font>

    <b>if</b><b>(</b>bAnimationWasOn<b>)</b>

    <b>{</b>

        info<b>.</b>iMinAnimate <b>=</b> <b>true</b><b>;</b>

        SystemParametersInfo<b>(</b>SPI_SETANIMATION<b>,</b> <b>sizeof</b><b>(</b>info<b>)</b><b>,</b> <b>&</b>info<b>,</b><font color="blue">0</font><b>)</b><b>;</b>

    <b>}</b>

<b>}</b>

</pre>

Many users configure their system to animate the frame of a window when it minimizes. This

animation can bog down the system when the code minimizes several windows. The code segment

above deactivates the animation before <TT>EnumWindows</TT> executes. The animization

setting is restored after all of the windows have been minimized to the taskbar.

</P>

<P>

The desktop will repaint itself after each window minimizes to the taskbar. This can cause

a lot of flashing. To reduce the amount of flashing, the code uses <TT>LockWindowUpdate</TT>

to prevent the desktop from repainting. Once all of the programs have been minimized, the

desktop is allowed to paint itself again.

</P>

<H4>Step 2: Minimizing each window</H4>

<P>

The callback function is shown below. This function is responsible for minimizing each

program. You can minimize a program by calling the <TT>ShowWindow</TT> API function and

passing it the <TT>SW_MINIMIZE</TT> parameter. Notice that the callback will only call

<TT>ShowWindow</TT> if the window is not owned by another window and if the window is

currently visible. Checking for ownership ensures that we don't minimize dialog boxes and

tool windows. These windows don't minimize to the taskbar, they minimize to the desktop.

Restoring these windows can be a pain. Windows will automatically hide owned windows when

we minimize their owner, so it's best to leave owned windows alone. We must also be careful

not to minimize a hidden window. Minimizing a hidden window makes it visible. Since there

is no way for the user to re-hide the window, minimizing a hidden window can royally screw

up the system (remove the <TT>IsWindowVisible</TT> check to see what I mean).

</P>

<pre>

BOOL CALLBACK MinimizeAllWindows<b>(</b>HWND hwnd<b>,</b>LPARAM lParam<b>)</b>

<b>{</b>

    <font color="navy">// determine if the window is owned by anyone</font>

    HWND hParent <b>=</b> GetWindow<b>(</b>hwnd<b>,</b> GW_OWNER<b>)</b><b>;</b>



    <font color="navy">// if the window is ownerless, and if it is visible,</font>

    <font color="navy">// then minimize it to the desktop</font>

    <b>if</b><b>(</b><b>(</b>hParent <b>==</b> NULL<b>)</b> <b>&&</b> IsWindowVisible<b>(</b>hwnd<b>)</b><b>)</b>

        ShowWindow<b>(</b>hwnd<b>,</b> SW_MINIMIZE<b>)</b><b>;</b>



    <font color="navy">// return true to continue the enumeration</font>

    <b>return</b> TRUE<b>;</b>

<b>}</b>

</pre>

<BR>

<P>

<B>Note:</B> Since the <TT>EnumWindows</TT> call references the <TT>MinimizeAllWindows</TT> callback

function, you should insert the body of the callback function above <TT>EnumWindows</TT> statement to avoid a compiler error. Alternatively, you could add a protoype for the callback function at

the top of the source file or in a header file.

</P>

<P>

<B>Note:</B> Notice that the callback function is not a member of any class. It just hangs

out in space all by itself. The callback function cannot be a regular method of a class

because the function is being called by Windows. Remember that all instances of a C++ class

share the same code. Objects contain unique data, but the functions are shared across all

objects. To identify which object is being acted on by a member function, C++ passes a

hidden <TT>this</TT> pointer to the member function. You can see the <TT>this</TT> pointer

if you view the assembly code of a function call. Unfortunately, Windows has no concept of

<TT>this</TT> pointers. Windows will execute the callback function like it is a regular

C style function that uses the <TT>__stdcall</TT> calling convention. It will not pass

a parameter where the <TT>this</TT> pointer would normally go. You could make the callback

function a static method of a class, since static methods don't take a <TT>this</TT> pointer.

But why bother. The function works fine on its own.

</P>



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