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<h3>FormContainer guide</h3>
<p>It's very easy to insert a form as a child window into another form with the use of <a
href="formcont.htm">FormContainer</a>. </p>
<p>First of all, you have to drop a FormContainer into the parent form. The FormContainer
component is located in the <em>FormContainer</em> palette. Its appearance is similar to a
panel, and you can also drop other controls into it, like in a panel.</p>
<p><a name="Form requirements">Next</a>, you need the form to insert as a child window. At
design time, the form has to fulfil some requirements:
<ol>
<li><em>BorderStyle</em> must be <em>bsNone</em></li>
<li><em>FormStyle</em> must be <em>fsNormal</em></li>
<li><em>WindowState</em> must be <em>wsNormal</em></li>
<li><em>Visible</em> must be <em>False</em></li>
</ol>
<p>At run time there are some considerations on using the form:
<ol>
<li>Never change form's visibility using <em>Show</em>, <em>Hide</em>, or the <em>Visible</em>
property of the form</li>
<li>Never call <em>ShowModal</em>, <em>Close</em>, <em>Destroy</em>, <em>Free</em> or <em>Release</em></li>
<li>Don't change <em>BorderStyle</em>, <em>FormStyle</em> and <em>WindowState</em></li>
<li>The <em>OnActivate</em> and <em>OnDeactivate</em> events are used as substitutes for the
<em>OnEnter</em> and <em>OnExit</em> events of the standard controls</li>
<li>The <em>OnClose</em> event is never fired</li>
<li>The <em>OnCloseQuery</em> event is only fired when you call <a
href="FormCont.htm#CloseQuery">CloseQuery</a> or <a href="FormCont.htm#CloseQueryAll">CloseQueryAll</a></li>
<li>The <em>OnShow</em> and <em>OnHide</em> events of a form are only fired when <a
href="FormCont.htm#ShowForm">ShowForm</a> or <a href="FormCont.htm#ShowFormEx">ShowFormEx</a>
are called directly or indirectly and the form is showed or hidden.</li>
</ol>
<p>To create the form, you have to obligatorily use the <a href="FormCont.htm#CreateForm">CreateForm</a>
method of the FormContainer. This way the form is created as a child window of the
FormContainer and attached to it for the rest of its life. For example:</p>
<pre> MyForm := TMyForm(MyFormContainer.CreateForm(TMyForm)));</pre>
<p>Here we have created a form called <em>MyForm</em> of class <em>TMyForm</em> and it is
a child window of MyFormContainer.</p>
<p>Once created, it is still not visible. To show it there are two methods: <a
href="FormCont.htm#ShowForm">ShowForm</a> and <a href="FormCont.htm#ShowFormEx">ShowFormEx</a>.</p>
<pre> MyFormContainer.ShowForm(MyForm, False);</pre>
<p>or</p>
<pre> MyFormContainer.ShowFormEx(MyForm, False, nil, nil, fcfaDefault);</pre>
<p>Here we have showed the form <em>MyForm</em>. If there were a previous visible form it
has been hidden, but not deleted (we could delete it specifying <em>True</em> at the
second parameter or calling <a href="FormCont.htm#DestroyForm">DestroyForm</a> at any
time). No transition has been used, we have not changed the <a
href="FormCont.htm#BackgroundOptions">BackgroundOptions</a>, and the form will be <a
href="formalig.htm#fcfaDefault">aligned</a> according to the form settings at design time.</p>
<p>All the forms attached to a FormContainer are accessible through the <a
href="FormCont.htm#Forms">Forms</a> property, and the visible one is returned by <a
href="FormCont.htm#Form">Form</a>.</p>
<p>When the FormContainer is destroyed all the attached forms are destroyed too.</p>
<p>FormContainer automatically maintains a <a name="LRU">LRU</a> (Last Recently Used) list
of forms. You can change the maximum number of elements of the list by setting <a
href="formcont.htm#LRUFormCapacity">LRUFormCapacity</a>. To return to one of these
previous used forms you can use: <a href="formcont.htm#ShowLRUForm">ShowLRUForm</a>, <a
href="formcont.htm#ShowLRUFormEx">ShowLRUFormEx</a>, <a
href="formcont.htm#ShowNextLRUForm">ShowNextLRUForm</a>, <a
href="formcont.htm#ShowNextLRUFormEx">ShowNextLRUFormEx</a>, <a
href="formcont.htm#ShowPriorLRUForm">ShowPriorLRUForm</a> or <a
href="formcont.htm#ShowPriorLRUFormEx">ShowPriorLRUFormEx</a>.</p>
<p>Destroyed forms are not included in the list unless you set <a
href="formcont.htm#SaveLRUDestroyedForms">SaveLRUDestroyedForms</a> to <em>True</em>. When
a previously destroyed form needs to be re-created automatically by the FormContainer
there is a mechanism to allow proper initialization of the form. For example, suppose you
have a form that contains an edit control and you need to initialize it with the text
previously entered into it by the user. You have to create a <a
href="formdata.htm#ExtraData">TFCExtraData</a> derived class and three <strong>published</strong>
methods for that form:</p>
<pre><strong> published</strong>
function FCGetExtraDataClass: TFCExtraDataClass;
procedure FCGetExtraData(ExtraData: TFCExtraData);
procedure FCSetExtraData(ExtraData: TFCExtraData);
...</pre>
<pre> TMyExtraData = class(TFCExtraData)
public
MyEditText: String;
end;
function TMyForm.FCGetExtraDataClass: TFCExtraDataClass;
begin
Result := TMyExtraData;
end;
procedure TMyForm.FCGetExtraData(ExtraData: TFCExtraData);
begin
MyEdit.Text := (ExtraData as TMyExtraData).MyEdit.Text;
end;
procedure TFormLRUSample.FCSetExtraData(ExtraData: TFCExtraData);
begin
(ExtraData as TMyExtraData).MyEditText := MyEdit.Text;
end;
</pre>
<p>You can see a sample of this in the 'LRU.pas' unit of the Demo project.</p>
<p>If the child form has a <em>TMainMenu</em> with <em>AutoMerge</em> set to <em>True</em>
then the menu will be <a name="menu merge">merged</a> with application's main menu when
showed.</p>
<p>You can show a <a href="FormCont.htm#Picture">Picture</a> as background of the
FormContainer with different <a href="FormCont.htm#BackgroundOptions">options</a> (tiled,
for example), and the alignment of the form can be controlled using the last parameter of <a
href="FormCont.htm#ShowFormEx">ShowFormEx</a> (for example, to force a form to be centered
on the FormContainer then simply call this function with <a href="formalig.htm#fcfaCenter">fcfaCenter</a>.</p>
<p>Each time the visible form is about to be switched the <a
href="FormCont.htm#OnFormChange">OnFormChange</a> event is called.</p>
<p>To hide the current visible form without showing another one just call:</p>
<pre> MyFormContainer.ShowForm(<strong>nil</strong>, False);</pre>
<p><a name="To use a transition">To use a transition</a> when showing and hiding forms,
just call <a href="FormCont.htm#ShowFormEx">ShowFormEx</a> passing it the desired
transition as parameter. </p>
<pre> var
Transition: TFuseTransition;
begin
Transition := TFuseTransition.Create;
try
Transition.Milliseconds := 500;
MyFormContainer.ShowFormEx(MyForm, False, <strong>Transition</strong>, nil, fcfaDefault);
finally
Transition.Free;
end;
end;</pre>
<p>If you want to use a <a href="flicker.htm">FlickerFreeTransition</a> it is easier to
set <a href="FormCont.htm#FlickerFree">FlickerFree</a> to <em>True</em>, because it is
equivalent.</p>
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