Lập trình Androi part 18 potx

CHAPTER 11: Applying Menus 133 Yet More Inflation Chapter 8 explained how you can describe Views via XML files and “inflate” them into actual View objects at runtime. Android also allows you to describe menus via XML files and inflate them when a menu is needed. This helps you keep your menu structure separate from the implementation of menu-handling logic, and it provides easier ways to develop menu-authoring tools. Menu XML Structure Menu XML goes in res/menu/ in your project tree, alongside the other types of resources that your project might employ. As with layouts, you can have several menu XML files in your project, each with its own filename and the .xml extension. For example, from the Menus/Inflation sample project, here is a menu called sample.xml: <?xml version="1.0" encoding="utf-8"?> <menu xmlns:android="http://schemas.android.com/apk/res/android"> <item android:id="@+id/close" android:title="Close" android:orderInCategory="3" android:icon="@drawable/eject" /> <item android:id="@+id/no_icon" android:orderInCategory="2" android:title="Sans Icon" /> <item android:id="@+id/disabled" android:orderInCategory="4" android:enabled="false" android:title="Disabled" /> <group android:id="@+id/other_stuff" android:menuCategory="secondary" android:visible="false"> <item android:id="@+id/later" android:orderInCategory="0" android:title="2nd-To-Last" /> <item android:id="@+id/last" android:orderInCategory="1" android:title="Last" /> </group> <item android:id="@+id/submenu" android:orderInCategory="3" android:title="A Submenu"> <menu> <item android:id="@+id/non_ghost" android:title="Non-Ghost" android:visible="true" android:alphabeticShortcut="n" /> <item android:id="@+id/ghost" android:title="A Ghost" android:visible="false" android:alphabeticShortcut="g" /> </menu> </item> </menu> CHAPTER 11: Applying Menus 134 Note the following about the XML for menus:  You must start with a menu root element.  Inside a menu element are item elements and group elements. The latter represents a collection of menu items that can be operated upon as a group.  Submenus are specified by adding a menu element as a child of an item element, using this new menu element to describe the contents of the submenu.  If you want to detect when an item is chosen, or to reference an item or group from your Java code, be sure to apply an android:id, just as you do with View layout XML. Menu Options and XML Inside the item and group elements, you can specify various options, matching up with corresponding methods on Menu or MenuItem, as follows:  Title: The title of a menu item is provided via the android:title attribute on an item element. This can be either a literal string or a reference to a string resource (e.g., @string/foo).  Icon: Menu items optionally have icons. To provide an icon, in the form of a reference to a drawable resource (e.g., @drawable/eject), use the android:icon attribute on the item element.  Order: By default, the order of the items in the menu is determined by the order in which they appear in the menu XML. You can change that by specifying the android:orderInCategory attribute on the item element. This is a 0-based index of the order for the items associated with the current category. There is an implicit default category. Groups can provide an android:menuCategory attribute to specify a different category to use for items in that group. Generally, it is simplest just to put the items in the XML in the order you want them to appear.  Enabled: Items and groups can be enabled or disabled, controlled in the XML via the android:enabled attribute on the item or group element. By default, items and groups are enabled. Disabled items and groups appear in the menu but cannot be selected. You can change an item’s status at runtime via the setEnabled() method on MenuItem, or change a group’s status via setGroupEnabled() on Menu. CHAPTER 11: Applying Menus 135  Visible: Items and groups can be visible or invisible, controlled in the XML via the android:visible attribute on the item or group element. By default, items and groups are visible. Invisible items and groups do not appear in the menu. You can change an item’s status at runtime via the setVisible() method on MenuItem, or change a group’s status via setGroupVisible() on Menu. In the layout XML shown in the previous section, the other_stuff group is initially invisible. If we make it visible in our Java code, the two menu items in the group will “magically” appear.  Shortcut: Items can have shortcuts—single letters (android:alphabeticShortcut) or numbers (android:numericShortcut) that can be pressed to choose the item without needing to use the touchscreen, D-pad, or trackball to navigate the full menu. Inflating the Menu Actually using the menu, once it’s defined in XML, is easy. Just create a MenuInflater and tell it to inflate your menu: @Override public boolean onCreateOptionsMenu(Menu menu) { theMenu=menu; new MenuInflater(getApplication()) .inflate(R.menu.sample, menu); return(super.onCreateOptionsMenu(menu)); } CHAPTER 11: Applying Menus 136 . xmlns:android="http://schemas.android.com/apk/res/android"> <item android:id="@+id/close" android:title="Close" android:orderInCategory="3" android:icon="@drawable/eject". <item android:id="@+id/no_icon" android:orderInCategory="2" android:title="Sans Icon" /> <item android:id="@+id/disabled" android:orderInCategory="4". android:orderInCategory="4" android:enabled="false" android:title="Disabled" /> <group android:id="@+id/other_stuff" android:menuCategory="secondary" android:visible="false">