When the two configurations differ then the current configuration is
updated eventually to reflect the requested configuration. An update
takes place when the following three conditions are fullfilled.
when the last pending request for configuration changes has been
processed,
when the configuration manager it is unlocked after formerly being
locked.
Requests for configuration changes are handled in a two step process:
First the requested configuration is updated iteratively: Every
request that is being made by calling
requestResourceActivation() or
requestResourceDeactivation() results in one or more
function objects, that each implement the
XConfigurationChangeRequest interface. These are inserted
into a queue. The request objects in the queue are processed
asynchronously one at a time in the order in which they are inserted.
Only when one request object is processed a change to the requested
configuration is made. These changes are broadcasted to registered
XConfigurationChangeListener objects. Listeners may
decide to make requests that then are added to the queue. For example
when the view in the center pane is replaced by another view, some
listeners may want to turn some side panes on or off, or show other
views in the side panes.
This process goes on until the queue of request objects becomes
empty. Until this point only the requested configuration has been
modified. No resources have been activated or deactivated.
The second update step activates or deactivates resources so that
the current configuration (the one that comprises the actually active
resources) reflects the requested configuration.
The order in which resources are activated or deactivated depends on
the dependency between the resources. For example a view depends on the
pane it is displayed in. Resources that other resources depend on are
activated first and deactivated last. The order is undefined for
unrelated resources.
Note that the second update step may not be able to activate (or even to
deactivate) all the requested resources. Either because they are
temporarily or permanently unavailable. For example, during the
start-up of a new Impress application the side panes are displayed
with a visible delay because they are not provided sooner by the
underlying framework. Such anavailable resources are not forgotten but
remain in the requested configuration. Every time the configuration
controller updates its current configuration these resources are
requested once more.
The configuration controller sends the following events:
ResourceActivationRequested is sent when the
activation of a resource has been requested and the resource is not yet
active in the requested configuration. The event is sent when the
configuration change request is executed, not when the
requestResourceActivation() call is made.
ResourceDeactivationRequested is sent when the
deactivation of a resource has been requested and the resource is active
in the requested configuration. The event is sent when the
configuration change request is executed that is created when for
example requestResourceDeactivation() is called.
ResourceDeactivation is sent when a resource is
deactivated, i.e. when an object that previously was part of the
configuration is removed from the configuration.
The request is processed asynchronously. Notifications about
configuration changes are sent after this call returns.
Parameter xResourceId
The resource whose activation is requested.
Parameter eMode
When eMode is REPLACE then, before adding the
resource activation to the request queue, similar resources
linked to the same anchor are removed. This makes it easer to
switch between resources whose activation is mutually exclusive.
For example, there can only be one view per pane, so before
activating a new view the old one has to be deactivated.
When eMode is ADD then the resource is requested
without further changes.
Lock the processing of configuration change requests.
This is only necessary when more than one change request is being
made in a row. It prevents an update being made (with all the visible UI
changes) before all change requests are being made.
Recursive lock() calls are recognized: the
configuration controller is locked while lock() was
called more often than unlock().
Unlock the processing of configuration change requests.
When unlock() is called as many times as
lock() and the queue of configuration change
requests is not empty the configuration controller continues the
processing of the change requests. An update of the current
configuration will eventually being made.
Explicitly request an update of the current configuration.
Call it when a resource is activated or deactivated
without the control and knowledge of the drawing framework. Calling
this method (from outside the drawing framework) should hardly every
be necessary.
Replace the requested configuration with the given configuration and
schedule an update of the current configuration.
Together with the getCurrentConfiguration() and
getRequestedConfiguration() methods this
allows the saving and restoring of configurations. However, the
given configuration can have other origins then these methods.
The given configuration is transformed into a list of of change
requests so that the resulting reqeusted configuration equals the
given configuration. This has the advantage that not only the
resource activations and deactivations but all configuration
changes are properly broadcasted.
Note that because of the configuration change notifications
listeners can make more configuratio change requests, so that the
resulting requested configuration can be different from the given
configuration.
