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   <TITLE>Create a control at runtime</TITLE>

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

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<H3>

Create a control at runtime

</H3>

<P>

<B>Step 1:</B> Add a variable to the form class that will contain the

component. Since this component is not being managed by the IDE, do not

put the declaration in the <B><TT>__published</TT></B> section. Also,

make sure the variable is listed as a pointer.</P>

<P>

<pre>

    <b>class</b> TForm1 <b>:</b> <b>public</b> TForm

    <b>{</b>

        <b>__published</b><b>:</b>   <font color="navy">// IDE-managed Components</font>

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

            TButton <b>*</b>OKButton<b>;</b>

        <b>...</b>

</pre>

</P>

<P>

Technically, the variable does not have to reside in the

form class that the control will appear in. You could place the <TT>OKButton</TT>

declaration in <TT>TForm1</TT>, even if you will display the button in another

form. However, you should avoid this practice for the sake of code

clarity.

</P>

<P>

<B>Step 2:</B> Create the control and assign properties. If you want the

control to appear when the form appears, place this code in the

constructor of the form.</P>

<P>

<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>

        OKButton <b>=</b> <b>new</b> TButton<b>(</b><b>this</b><b>)</b><b>;</b>

        OKButton<b>-></b>Parent  <b>=</b> <b>this</b><b>;</b>

        OKButton<b>-></b>Caption <b>=</b> <font color="blue">"Dynamic Button"</font><b>;</b>

        OKButton<b>-></b>SetBounds<b>(</b><font color="blue">10</font><b>,</b><font color="blue">10</font><b>,</b><font color="blue">110</font><b>,</b><font color="blue">25</font><b>)</b><b>;</b>

    <b>}</b>

</pre>

</P>

<P>

<B>Note:</B> The contol will not appear if you forget to assign the <TT>Parent</TT> property.

</P>

<P>

<B>Note:</B> For most dynamic controls, you will need to assign an event handler in code. This

task is separated into a different question. See the FAQ listed as how do I

<A HREF="../events messages/faq1.htm">assign event handlers at runtime</A>. The example below assigns an <TT>OnClick</TT>

handler for the button.

</P>

<pre>

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

    <b>class</b> TForm1 <b>:</b> <b>public</b> TForm

    <b>{</b>

        <b>__published</b><b>:</b>   <font color="navy">// IDE-managed Components</font>

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

            TButton <b>*</b>OKButton<b>;</b>

            <b>void</b> <b>__fastcall</b> ButtonClick<b>(</b>TObject <b>*</b>Sender<b>)</b><b>;</b>

        <b>...</b>

        <b>...</b>



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

    <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>

        OKButton <b>=</b> <b>new</b> TButton<b>(</b><b>this</b><b>)</b><b>;</b>

        OKButton<b>-></b>Parent  <b>=</b> <b>this</b><b>;</b>

        OKButton<b>-></b>Caption <b>=</b> <font color="blue">"Dynamic Button"</font><b>;</b>

        OKButton<b>-></b>SetBounds<b>(</b><font color="blue">10</font><b>,</b><font color="blue">10</font><b>,</b><font color="blue">110</font><b>,</b><font color="blue">25</font><b>)</b><b>;</b>



        OKButton<b>-></b>OnClick <b>=</b> ButtonClick<b>;</b>

    <b>}</b>



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

    <b>{</b>

        <font color="navy">// handler code here</font>

    <b>}</b>

</pre>



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