Книга: Beginning Android

Would You Like to See the Menu?

Would You Like to See the Menu?

Another way to give the user ways to take actions on a piece of content, without you knowing what actions are possible, is to inject a set of menu choices into the options menu via addIntentOptions(). This method, available on Menu, takes an Intent and other parameters and fills in a set of menu choices on the Menu instance, each representing one possible action. Choosing one of those menu choices spawns the associated activity.

The canonical example of using addIntentOptions() illustrates another flavor of having a piece of content and not knowing the actions that can be taken. In the previous example, showing ActivityAdapter, the content was from some other Android application, and we know nothing about it. It is also possible, though, that we know full well what the content is — it’s ours. However, Android applications are perfectly capable of adding new actions to existing content types, so even though you wrote your application and know what you expect to be done with your content, there may be other options you are unaware of that are available to users.

For example, imagine the tagging sub-system mentioned in the introduction to this chapter. It would be very annoying to users if every time they wanted to tag a piece of content, they had to go to a separate tagging tool then turn around and pick the content they just had been working on (if that is even technically possible) before associating tags with it. Instead they would probably prefer a menu choice in the content’s own “home” activity where they can indicate they want to tag it, which leads them to the set-a-tag activity and tells that activity what content should get tagged.

To accomplish this, the tagging sub-system should set up an Intent filter, supporting any piece of content with its own action (e.g., ACTION_TAG) and a category of CATEGORY_ALTERNATIVE, which is the convention for one application adding actions to another application’s content.

If you want to write activities that are aware of possible add-ons like tagging, you should use addIntentOptions() to add those add-ons’ actions to your options menu, such as the following:

Intent intent = new Intent(null, myContentUri);
intent.addCategory(Intent.ALTERNATIVE_CATEGORY);
menu.addIntentOptions(Menu.ALTERNATIVE, 0,
 new ComponentName(this, MyActivity.class), null, intent, 0, null);

Here, myContentUri is the content Uri of whatever is being viewed by the user in this activity, MyActivity is the name of the activity class, and menu is the menu being modified.

In this case, the Intent we are using to pick actions from requires that appropriate Intent receivers support the CATEGORY_ALTERNATIVE. Then we add the options to the menu with addIntentOptions() and the following parameters:

• The sort position for this set of menu choices, typically set to 0 (which appear in the order added to the menu) or ALTERNATIVE (which appear after other menu choices).

• A unique number for this set of menu choices, or 0 if you do not need a number.

• A ComponentName instance representing the activity that is populating its menu — this is used to filter out the activity’s own actions so the activity can handle its own actions as it sees fit.

• An array of Intent instances that are the “specific” matches — any actions matching those Intents are shown in the menu before any other possible actions.

• The Intent for which you want the available actions.

• A set of flags. The only one of likely relevance is represented as MATCH_DEFAULT_ONLY, which means matching actions must also implement the DEFAULT_CATEGORY category. If you do not need this, use a value of 0 for the flags.

• An array of Menu.Items, which will hold the menu items matching the array of Intent instances supplied as the “specifics,” or null if you do not need those items (or are not using “specifics”).

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