[MUSIC]. In addition to what I've just shown you, menus can also support a number of more advanced features. For example, you can put related menu items into a group so you can process and manipulate them as a unit. You can also bind shortcut keys to specific menu items so you can access them more quickly. And you can bind intents to menu items. So for instance, you can start a particular activity, when the user clicks on a particular menu item. So I've mentioned the ActionBar a few times now. The ActionBar bar was added in android 3.0 and kind of mimics the Application Bar, that you often see in desktop apps, desktop applications. You know, that bar at the top of the application window that just says things like File, Edit, Help and those things. And the basic idea behind the ActionBar is that rather than hiding actions behind a traditional pop-up menu. You want to give the users quick access to the actions that they're likely to use. Let's look at some uses of the ActionBar. Now the first example I'll give goes back to our lesson on fragments. You remember those core viewer applications? Well in this application fragment dynamic layout with ActionBar. I've added some items to the ActionBar. Now as you'll see in a minute, these items are provided by three different classes. Some items come from the main activity. Some come from the fragment that displays the titles. And some come from the fragment that displays the quotes. Let's take a look. Here's my emulated tab. Now I'll start the application. And as before, when it starts up, there's a main activity which hosts a single fragment, the title fragment. Now if we look at the ActionBar at the top of the tablet, you see that there are two bits of text in the upper right corner. One says activity action. And the other says title action. That first piece of text was put there by the code viewer activity. The second was put there by the title fragment. And if I click on these bits of text, you'll see some text pop up, letting you know which object is actually carrying out the actions associated with that ActionBar r item. Now if I click on one of the titles. You remember that this causes the quote fragment to be dynamically added to the layout. Well, the quote fragment also adds some items to the ActionBar dynamically. In this case, there's a main action and a second action that gets put into the overflow area. So I'll click on the main action. And, again, you can see the text saying that this action was provided by the quote fragment. If I click on the overflow icon, this causes the second item provided by the quote fragment, to appear. And if I now click on that pop-up. You again see the associated text pop up. Now let's look at how this is implemented in the source code. Here I've opened the application in the IDE. I'll first open the quote viewer activity file, and there you'll see the on create options menu. And on options menu item selected methods. The same as we talked about before. Not much new here. Let's take a look at the menu layout and the activity underscore, menu.xml file. And this looks like what we've already seen. But one difference is the show as action attribute. It's value is, if room or with a text. And this means that Android should show this item in the ActionBar if there's room. But it should put it in the overflow area, otherwise. It also means that the item should be shown as text rather than by displaying, say an icon. Now, I'll open up the title fragment fla, file, and again, there are calls to the on create options menu and on options menu item selected methods. The one difference here is that because title fragment is a fragment, we also have to issue the command set has options true, which we do in the on create method. And last, I'll open up the quote fragment file. Again, not much new here. The quote fragment has this menu file in quote_menu.xml, and let's look at that. This menu has two items. One has its showAsAction attribute set to ifRoom|withText just like we saw before. The other one though has its showAsAction attribute set to never. And so it will always appear in the overflow area. And never in the ActionBar. Another use of the ActionBar, is to help provide a consistent way of switching between different views in an application. When using the ActionBar this way the screen is divided into two sections. A tab area and a content area. The ActionBar on tab class allows you to associate a fragment with each tab indicator in the tab area. Now, only one tab indicator can be selected at any one time. So when the user selects a particular tab indicator. Its fragment can be shown in the content area. If the user then selects a different tab, a different fragment can be shown in the content area. So here's a sample application called UITabLayout that uses the ActionBar.Tab class to switch between two instances. Of a fragment that uses the grid view layout that we discussed earlier. Here I'll start the UI Tab Layout application. The application displays two tab indicators, one labeled flowers, and one labeled animals. The flowers tab is currently selected. And in fact does exactly what we saw in the UI grid view application. Now I'll select the animals tab. As you can see the application is now displaying another grid view fragment, but this time it's showing images of dogs rather than flowers. Let's take a look at the source code for this application. Here's the application open in the IDE. I'll now open the tab layout activity file and go to the onCreate method. First, the code gets the ActionBar. Then it configures the ActionBar r to operate as a tab. Next I create the grid view fragment giving it the list of images that it should display. And in this case that's the flower images. Finally I create and configure a new tab indicator and attach it to the ActionBar. And I'll do essentially the same thing with the other tab. Now, when I added the tab, notice that I also created an instance of something called the tab listener. And this is an object that will be called when the user selects and unselects individual tabs. Let me scroll down to that code. Now, here's the onTabSelected method. When a tab is selected this code adds its fragment to the hosting activity. Here's the onTabUnselected method. When a tab is unselected, this code removes the current fragment. From the hosting activity. The last thing I want to discuss are dialogues. A dialogue is a kind of independent sub window that is used by an activity for short communications with users. Some dialogue classes provided by Android, include the alert dialogue. A ProgressDialog and a Date and TimePicker Dialogs. Let's look at a sample application that uses both the AlertDialog and the ProgressDialog. Here's the UIAlertDialog application. When I started up, it displays one button. That the user can press to initiate application shut down. Let me hit that button now. When I do that, you see that the application pops up a dialog, an alert dialog that shows a message, do you really want to exit? And it allows the user to respond. In this case either yes or no. I'll hit no now. Which simply dismisses the alert dialog and returns me back to the application. Let's say some time goes by. And now I really do want to exit. So I'll hit the shutdown button again. Which again brings up the alert dialog. This time however, I'll hit the yes button on the alert dialog. And at this point the alert dialog is dismissed, and a new dialog, this time a progress dialog is displayed. Which shows a graphic spinner. To let me know that the shutdown process is proceeding. Eventually the shutdown finishes and the application terminates itself. Let's see what this looks like in the source code. So here's the application in the IDE. I'll open up the alert dialog activity file and go to it's on create method. As you can see when the user presses the shut down button the showed dialog fragment method is invoked, passing in an I.D. for the desired dialog. The showed dialog fragment method. Creates an instance of the AlertDialogFragment, and then calls the show method on it. Let's look at that class. AlertDialogFragment is a subclass of DialogFragment. And it has an onCreateDialog method. This method will be called in response to a show method. Being invoked. And this method creates a new alert dialog dot builder instance. The methods of a builder almost always return the current object, and this is useful because it allows you to create an object, and then just keep tacking on method calls one after another. To configure that object. In fact, here you can see a call to setMessage. And right after that, a call to setCancelable, then a call to setNegativeButton, and so forth. And once you set all the things that you want, you end with a call to the create method. Which effectively puts together all of the previous calls, and returns the final configured object. Now once this dialog is displayed, if the user selects no, then there's a call to shut down, continue with the perimeter false. If the user instead selects yes, then there's a call to shut down continue with the parameter true. Let's go the shutdown continue method. So if should continue is false, then we dismiss the alert dialog and everything goes on as if nothing had happened. If shouldContinue is true, however, we dismiss the alert dialogue and then call showDialogue passing in the progress tag ID. And this call creates a progress dialogue fragment object. And then calls the show method on it. Eventually we end up at the on create dialogue method in the progress dialogue fragment class and here we make a new progress dialogue, set it's message to activity shutting down, and then call set indeterminate true. Which allows the dialog to stay visible until it's dismissed.
