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   <TITLE>Create and remove menu items from code.</TITLE>

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

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<H3>

Create and remove menu items from code.

</H3>

<br>

<h3>Background information:</H3>

<P>

Both <TT>TMainMenu</TT> and <TT>TPopupMenu</TT> contain an <TT>Items</TT> property. The <TT>Items</TT> property

returns a <TT>TMenuItem</TT> pointer. The <TT>TMenuItem</TT> that is returned by the <TT>Items</TT> property

represents an invisible root item that contains all of the menu items in the control. Think of this item as the

root node of a tree view control. The only difference is that the root node of a tree view is visible.

</P>

<TT>TMenuItem</TT> has a <TT>Count</TT> property that returns the number children that are owned by the menu item.

<TT>TMenuItem</TT> also contains an <TT>Items</TT> property. This property allows you to access all of the child menu

items of the parent item. For example, imagine that your program has three main menu items called File, Edit and Help.

The <TT>Items</TT> property of <TT>TMainMenu</TT> will return the invisible root item. The <TT>Count</TT> property of

the root item will be three. The <TT>Items</TT> property of the root menu item will contain three child items: one

for File, one for Edit, and one for Help. The following code explains this concept further.

</P>

<pre>

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

<b>{</b>

    ListBox1<b>-></b>Items<b>-></b>Clear<b>(</b><b>)</b><b>;</b>



    TMenuItem <b>*</b>Root <b>=</b> MainMenu1<b>-></b>Items<b>;</b>



    Label1<b>-></b>Caption <b>=</b> IntToStr<b>(</b>Root<b>-></b>Count<b>)</b><b>;</b>

    <b>for</b><b>(</b><b>int</b> j<b>=</b><font color="blue">0</font><b>;</b> j&lt;Root<b>-></b>Count<b>;</b> j<b>++</b><b>)</b>

        ListBox1<b>-></b>Items<b>-></b>Add<b>(</b>Root<b>-></b>Items<b>[</b>j<b>]</b><b>-></b>Caption<b>)</b><b>;</b>

<b>}</b>

</pre>

<P>

This code isn't all that useful, but it does explain how the root menu item works. The code takes the top level

menu items and inserts a string into a listbox for each one. If your program has top level menu items call File,

Edit, and Help, then the code would put File, Edit, and Help into the listbox.

</P>

<P>

Most top level menu items contain other menu items as children. These child items can be accessed through the

<TT>Items</TT> property of their parent. The following code places a string in a listbox for every menu item below

the first top level menu item in the program.

</P>

<pre>

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

<b>{</b>

    ListBox1<b>-></b>Items<b>-></b>Clear<b>(</b><b>)</b><b>;</b>



    TMenuItem <b>*</b>Root <b>=</b> MainMenu1<b>-></b>Items<b>;</b>

    <b>if</b><b>(</b>Root<b>-></b>Count <b>==</b> <font color="blue">0</font><b>)</b>

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



    TMenuItem <b>*</b>FirstItem <b>=</b> Root<b>-></b>Items<b>[</b><font color="blue">0</font><b>]</b><b>;</b>

    <b>for</b><b>(</b><b>int</b> j<b>=</b><font color="blue">0</font><b>;</b> j&lt;Root<b>-></b>Count<b>;</b> j<b>++</b><b>)</b>

        ListBox1<b>-></b>Items<b>-></b>Add<b>(</b>FirstItem<b>-></b>Items<b>[</b>j<b>]</b><b>-></b>Caption<b>)</b><b>;</b>

<b>}</b>

</pre>

<P>

Of course, you don't have to retrieve the menu items from the <TT>Items</TT> property if your form class already contains

<TT>TMenuItem</TT> pointers for all the menu items in your program.

</P>

<P>

<TT>TMenuItem</TT> contains a host of functions for adding and removing menu items. The <TT>Add</TT> method of <TT>TMenuItem</TT>

adds a new child menu at the end of any existing menu items. The <TT>Add</TT> function takes a <TT>TMenuItem</TT> pointer

as an argument. You must construct the menu item in code, assign its properties, and then call <TT>Add</TT> to make the

item appear. <TT>Insert</TT> works just like the <TT>Add</TT> method, except that it takes an extra index argument that

specifies where the new menu item should appear. You can delete a child menu item by calling the <TT>Delete</TT> method

of its parent. <TT>Delete</TT> takes an integer index that determines which item should be nuked. You can also delete a

child menu item by calling the <TT>Remove</TT> method. <TT>Remove</TT> takes a pointer to the menu item that should be

deleted.

</P>

<P><B>Note:</B> Both the <TT>Remove</TT> function and the <TT>Delete</TT> function delete the <TT>TMenuItem</TT> pointer

that they remove from the menu. You can no longer reference the menu item was you <TT>Remove</TT> or <TT>Delete</TT> it.

For this reason, you probably should not <TT>Remove</TT> or <TT>Delete</TT> menu items that were created at design time,

because those items have data members in the form class.

</P>

<H3>Adding new top-level menu items</H3>

<P>

This code adds a new top level menu item called Help, and several child menu items under the top level item.

</P>

<pre>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button4Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    TMenuItem <b>*</b>Root <b>=</b> MainMenu<b>-></b>Items<b>;</b>



    <font color="navy">// create a new menu item, set the owner to the form;</font>

    TMenuItem <b>*</b>HelpItem <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    HelpItem<b>-></b>Caption <b>=</b> <font color="blue">"&Help"</font><b>;</b>

    Root<b>-></b>Add<b>(</b>HelpItem<b>)</b><b>;</b>



    <font color="navy">// now add child items under the new Help item.</font>

    TMenuItem <b>*</b>ContentsItem <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    TMenuItem <b>*</b>IndexItem    <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    TMenuItem <b>*</b>AboutItem    <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    ContentsItem <b>-></b>Caption <b>=</b> <font color="blue">"&Contents"</font><b>;</b>

    IndexItem    <b>-></b>Caption <b>=</b> <font color="blue">"&Index"</font><b>;</b>

    AboutItem    <b>-></b>Caption <b>=</b> <font color="blue">"&About"</font><b>;</b>



    HelpItem<b>-></b>Add<b>(</b>ContentsItem<b>)</b><b>;</b>

    HelpItem<b>-></b>Add<b>(</b>IndexItem<b>)</b><b>;</b>

    HelpItem<b>-></b>Add<b>(</b>AboutItem<b>)</b><b>;</b>

<b>}</b>

</pre>



<H3>Adding nested menus</H3>

<P>

This code adds new child items to an existing menu item. The code creates a menu that resembles the File | Reopen

menu option in the C++Builder IDE.

</P>

<pre>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button5Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    <font color="navy">// existing menu item is a member variable called Reopen1</font>

    <font color="navy">// and four child menu items</font>

    TMenuItem <b>*</b>Child1 <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    TMenuItem <b>*</b>Child2 <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    TMenuItem <b>*</b>Child3 <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>

    TMenuItem <b>*</b>Child4 <b>=</b> <b>new</b> TMenuItem<b>(</b><b>this</b><b>)</b><b>;</b>



    Child1<b>-></b>Caption <b>=</b> <font color="blue">"c:\\cbuilder3\\projects\\project1.bpr"</font><b>;</b>

    Child2<b>-></b>Caption <b>=</b> <font color="blue">"c:\\cbuilder3\\projects\\project2.bpr"</font><b>;</b>

    Child3<b>-></b>Caption <b>=</b> <font color="blue">"-"</font><b>;</b> <font color="navy">// separator bar</font>

    Child4<b>-></b>Caption <b>=</b> <font color="blue">"c:\\cbuilder3\\projects\\unit1.cpp"</font><b>;</b>



    Child1<b>-></b>Default <b>=</b> <b>true</b><b>;</b>



    Reopen1<b>-></b>Add<b>(</b>Child1<b>)</b><b>;</b>

    Reopen1<b>-></b>Add<b>(</b>Child2<b>)</b><b>;</b>

    Reopen1<b>-></b>Add<b>(</b>Child3<b>)</b><b>;</b>

    Reopen1<b>-></b>Add<b>(</b>Child4<b>)</b><b>;</b>

<b>}</b>

</pre>



<H3>Removing a menu item</H3>

<P>

This code removes the last top level menu item. All children of this item are also destroyed.

</P>

<pre>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>Button6Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    TMenuItem <b>*</b>Root <b>=</b> MainMenu1<b>-></b>Items<b>;</b>

    <b>if</b><b>(</b>Root<b>-></b>Count <b>></b> <font color="blue">0</font><b>)</b>

        Root<b>-></b>Delete<b>(</b>Root<b>-></b>Count <b>-</b><font color="blue">1</font><b>)</b><b>;</b>

<b>}</b>

</pre>

<H3>Adding and Removing a menu item without deleting the object</H3>

<P>

As mentioned earlier, removing a menu item deletes the menu item pointer. This might be a problem if you want to

add and remove the same menu item repeatedly. Instead of calling the <TT>Add</TT> and <TT>Remove</TT> methods, you can

simply toggle the <TT>Visible</TT> property of a menu item. This keeps the menu item pointer intact. Here is a code

example that hides or shows the Edit menu based on the state of a check box. Notice that hiding a parent item hides all

of its child items.

</P>

<pre>

<b>void</b> <b>__fastcall</b> TForm1<b>:</b><b>:</b>CheckBox1Click<b>(</b>TObject <b>*</b>Sender<b>)</b>

<b>{</b>

    EditMenuItem<b>-></b>Visible <b>=</b> CheckBox1<b>-></b>Checked<b>;</b>

<b>}</b>

</pre>



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