### Activities

An activity is a logical grouping of function that is centered around a certain kind of task. For example, developing Java software is an activity commonly performed by users of the platform, and the JDT defines many UI contributions (views, editors, perspectives, preferences, etc.) that are only useful when performing this activity. Before we look at the mechanics for defining an activity, let's look at how they are used to help "declutter" the UI.

The concept of an activity is exposed to the user, although perhaps not apparent to a new user. When an activity is enabled in the platform, the UI contributions associated with that activity are shown. When an activity is disabled in the platform, its UI contributions are not shown. Users can enable and disable activities as needed using the General > Capabilities preference page. (Activities are referred to as "capabilities" in the user interface, even though we use activity terminology in the API).

Certain user operations serve as trigger points for enabling an activity. For example, creating a new Java project could trigger the enabling of the Java development activity. In this way, users are exposed to new function as they need it, and gradually learn about the activities that are available to them and how they affect the UI. When a user first starts the platform, it is desirable for as many activities as possible to be disabled, so that the application is as simple as possible. Choices made in the welcome page can help determine what activities should be enabled.

### Activities vs. perspectives

We've seen (in Perspectives) how perspectives are used to organize different view layouts and action sets into tasks. Why do we need activities? While perspectives and activities define similar kinds of tasks, the main difference is how the UI contributions for a plug-in are associated with them. UI contributions are associated with perspectives in the extension definition of the contribution. That is, a plug-in is in charge of determining what perspectives its views and action sets belong to. Plug-ins are also free to define their own perspectives. Even when a perspective is not active, the user can access the views and actions associated with the perspective through commands such as Show View.

Activities are a higher level of organization. Individual UI contributions are not aware of activities and do not refer to the activities in their extension definitions. Rather, the activities are expected to be configured at a higher level such as platform integration/configuration or product install. Individual plug-ins typically do not define new activities, unless the plug-in is a systems-level plug-in defined by a systems integrator. In a typical scenario, a systems integrator determines how function is grouped into activities and which ones are enabled by default. Activities are associated with UI contributions using activity pattern bindings, patterns that are matched against the id of the UI contributions made by plug-ins. An example will help demonstrate these concepts.

#### Defining an activity

Activities are defined using the org.eclipse.ui.activities extension point. Let's look at a simplified version of how the Eclipse SDK plug-in defines two activities - one for developing Java software and one for developing plug-ins:

    <extension
    	point="org.eclipse.ui.activities">
    	<activity
    		name="Java Activity"
    		description="Developing Java Software"
    		id="org.eclipse.javaDevelopment">
    	</activity>

    	<activity
    		name="Plug-in Activity"
    		description="Developing Eclipse Plug-ins"
    		id="org.eclipse.plugInDevelopment">
    	</activity>
    	...

Activities are assigned a name and description that can be shown to the user whenever the user is enabling and disabling activities, or otherwise shown information about an activity. The id of the activity is used when defining pattern bindings or other relationships between activities. For example, we can decide that one activity requires another activity.

    <activityRequirementBinding
    	activityId="org.eclipse.plugInDevelopment"
    	requiredActivityId="org.eclipse.javaDevelopment">
    </activityRequirementBinding>

The requirement binding states that the plug-in development activity can only be enabled when the Java development activity is enabled. Related activities can also be bound into categories, that are shown to the user when the user is working with activities.

    <category
    	name="Development"
    	description="Software Development"
    	id="org.eclipse.categories.developmentCategory">
    </category>

    <categoryActivityBinding
    	activityId="org.eclipse.javaDevelopment"
    	categoryId="org.eclipse.categories.developmentCategory">
    </categoryActivityBinding>

    <categoryActivityBinding
    	activityId="org.eclipse.plugInDevelopment"
    	categoryId="org.eclipse.categories.developmentCategory">
    </categoryActivityBinding>

The category groups the related development activities together. This category is shown to the user when the user manually configures activities.

#### Binding activities to UI contributions

Activities are associated with UI contributions using pattern matching. The pattern matching used in activity pattern bindings follows the rules described in the java.util.regex package for regular expressions. The patterns used by the workbench are composed of two parts. The first part uses the identifier of the plug-in that is contributing the UI extension. The second part is the id used by plug-in itself when defining the contribution (which may or may not also include the plug-in id as part of the identifier). The following format is used:

    plug-in-identifier + "/" + local-identifier

For example, the following activity pattern binding states that a UI contribution from any JDT plug-in id (`org.eclipse.jdt.*`) is associated with the Java development activity regardless of its local identifier (`.*`).

    <activityPatternBinding
    	activityId="org.eclipse.javaDevelopment"
    	pattern="org\.eclipse\.jdt\..*/.*">
    </activityPatternBinding>

The next binding is more specific. It states that the contribution named `javanature` defined in the JDT core (`org.eclipse.jdt.core`) is associated with the Java development activity.

    <activityPatternBinding
    	activityId="org.eclipse.javaDevelopment"
    	pattern="org\.eclipse\.jdt\.core/javanature">
    </activityPatternBinding>

As you can see, activity pattern bindings can be used to associate large groups of contributions with a particular activity, or to associate very specific contributions to an activity. The following contributions are affected by activities:

- Views and editors
- Perspectives
- Preference and property pages
- Menus and toolbars
- New project wizard

The convention used by the workbench (plug-in id + local id) allows easy binding to plug-ins that do not necessarily follow the naming practice of prefixing their UI contribution identifiers with their plug-in's identifier. Plug-ins that directly interact with the activity API are free to use their own format for identifying contributions and for pattern-matching against those names.

#### Binding activities to help contributions

Activities are associated with help contributions using the same pattern matching scheme used for UI contributions. The second part of the identifier (the local identifier) indicates the name of the table of contents (TOC) file. For example, the following activity pattern binding associates all TOC files contributed by JDT plug-ins (org.eclipse.jdt.*) with the Java development activity:

    <activityPatternBinding
    	activityId="org.eclipse.javaDevelopment"
    	pattern="org\.eclipse\.jdt\..*/.*">
    </activityPatternBinding>

When the Java development activity is disabled, help books contributed by JDT plug-ins, or any sub-books (TOCs linked to, or linked by JDT books), even if contributed by a different plug-in, will not show in the help UI. The topics defined in these books will also not show in the search results. In the case where JDT TOCs were not displayed as primary TOCs, but were instead linked from another TOC to appear as sub-trees in a book, disabling the JDT activity has the effect of hiding the sub-trees. The containing book will appear to define less topics in the UI.

Using more specific binding, it is possible to associate activities with selected TOCs from plug-ins that contribute multiple TOCs to the help system. For example, the following activity pattern binding associates the "Examples" TOC with the Java development examples activity.

    <activityPatternBinding
    	activityId="org.eclipse.javaDevelopmentExamples"
    	pattern="org\.eclipse\.jdt\.doc\.isv\.topics_Samples.xml">
    </activityPatternBinding>

With such pattern binding, disabling the Java development examples activity will hide the "Examples" section from the "JDT Plug-in Developer Guide" book.

#### Using the activities API

The workbench activity support includes an API for working with the defined activities and changing their enabled state. Most plug-ins need not be concerned with this API, but it is useful when implementing function that allows the user to work with activities, or for implementing the trigger points that enable a particular activity. It is assumed that any plug-in that is manipulating activities through API is quite aware of the ways that activities are configured for a particular product. For example, the workbench itself uses the API to trigger the enablement of activities such as Java development. We'll look at how the workbench uses the generic activity API to implement triggers.

The hub of all activity in the workbench is IWorkbenchActivitySupport. The activity support works in tandem with an IActivityManager. Plug-ins can obtain the activity support instance from the workbench, and the activity manager from there.

    IWorkbenchActivitySupport workbenchActivitySupport = PlatformUI.getWorkbench().getActivitySupport();
    IActivityManager activityManager = workbenchActivitySupport.getActivityManager();

The following snippet enables the Java development activity (if it is not already enabled). It shows a simplified version of a trigger.

    ...
    //the user did something Java related.  Enable the Java activity.
    Set enabledActivityIds = new HashSet(activityManager.getEnabledActivityIds());
    if (enabledIds.add("org.eclipse.javaDevelopment"))
    	workbenchActivitySupport.setEnabledActivityIds(enabledActivityIds);

IActivityManager also defines protocol for getting all defined activity and category ids, and for getting the associated IActivity or ICategory for a particular id. These objects can be used to traverse the definition for an activity or category in API, such as getting the pattern bindings or requirement bindings. Listeners can be registered on the activity manager or on the activities and categories themselves to detect changes in the definition of a particular activity or in the activity manager itself. See the package org.eclipse.ui.activities for more information.