54 Menu Resources, Option Menu | Android app development tutorial for beginners using Android studi

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A menu resources defines an application menu like option menu, context menu or sub menu which can be inflated with MenuItem or Inflator.

File location:
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res/menu/filename.xml
The filename will be used as resource id.
Resource Reference:
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In Java R.menu.filename
in xml @[package:]menu-filename
Defining Menu in XML:
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For all menu types android provides a standard XML format to define menu items, Instead of building a menu in our activity code, you should define a menu and all items in an XML menu resource, so you can inflate these menu resource in your activity or a fragment.
To define menu, create a XML file inside your project/app under res/menu directory.

elements:
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menu:
Defines a menu, which is a container for menu item, A menu element must be the root node for the file and can hold one or more item and group elements.

item:
creates a MenuItem, which represents a single item in a menu. This element may contain a nested menu element in order to create submenu.

group:
An optional, invisible container for item elements, it allows you to categorize menu items by creating menu groups.

1) android:id - A resource id that is unique to the item.
2) android:title - The reference to a string to use as the items title
3) android:icon - The reference to a drawable to use as the itmes icon.
4) app:showAsAction - Specifies when and how this itmes should appear as action item in the app bar.

values of app:showAsAction attribute-

value Description
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ifRoom Only place this item in the app bar if there is room/space for it
never Never place this item in the app bar
always Always place this itme in the app bar.
withText Also include the title text (defined by android:title) with the action item. you can include this value along with one of the others as flag set by seperating them with a pipe.
5) android:checked="true/false"
Boolean, "true" if item is checked by default.

In android menus are categorized into 3 types:
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1) Option Menu & App bar.
2) Context menu, and contextual action mode.
3) Pop menu.


1) Option Menu or App Bar:
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The options menu will have global impact on the app such as search, compose mail, settings etc...

The option menu is the primary collection of menu items for an activity, if we are developing for Android 2.3 or lower version users can see/reveal the option panel by pressing the menu button.

In android 3.0 & higher version, items from the option menu are presented by the app bar as a combination of on screen items & overflow options.