Package org.eclipse.jface.resource

Class DeviceResourceDescriptor

java.lang.Object

org.eclipse.jface.resource.DeviceResourceDescriptor

Direct Known Subclasses:

ColorDescriptor, FontDescriptor, ImageDescriptor

public abstract class DeviceResourceDescriptor
extends Object

Instances of this class can allocate and dispose SWT resources. Each instance describes a particular resource (such as a Color, Font, or Image) and can create and destroy that resource on demand. DeviceResourceDescriptors are managed by a ResourceRegistry.

Note: It is recommended that subclasses implement #equals and #hashCode, so that clients, like decoration managers, can recognize when they have two equal descriptors at hand, e.g. decorating an identical object.

Since:

3.1

See Also:

ResourceManager

Constructor Summary

Constructors

Modifier	Constructor	Description
	DeviceResourceDescriptor()	default constructor with shouldBeCached=false
protected	DeviceResourceDescriptor(boolean shouldBeCached)

Method Summary

Modifier and Type	Method	Description
abstract Object	createResource(Device device)	Creates the resource described by this descriptor
abstract void	destroyResource(Object previouslyCreatedObject)	Undoes everything that was done by a previous call to create(...), given the object that was returned by create(...).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DeviceResourceDescriptor

public DeviceResourceDescriptor()

default constructor with shouldBeCached=false

DeviceResourceDescriptor

protected DeviceResourceDescriptor(boolean shouldBeCached)

Parameters:

shouldBeCached - Indicates if the resource instance described by the descriptor should to be kept by ResourceManager even if all references to the resource are lost (due to ResourceManager.destroy(DeviceResourceDescriptor)).
Should return true for resources that are costly to create (for example by involving I/O Operation). Has only an effect if caching is enabled (see org.eclipse.jface.resource.JFaceResources#cacheSize). Caching relies on Object.equals(Object) and Object.hashCode(). For equal DeviceResourceDescriptors the same Resource instance is returned by the ResourceManager instance return by JFaceResources.getResources(org.eclipse.swt.widgets.Display) as long as the cache is big enough to cache all resources.
Instances which equal (in terms of Object.equals(Object)) must have the same shouldBeCached mode.

Since:

3.24

See Also:

LazyResourceManager

Method Detail

createResource

public abstract Object createResource(Device device)

Creates the resource described by this descriptor

Parameters:

device - the Device on which to allocate the resource

Returns:

the newly allocated resource (not null)

Throws:

DeviceResourceException - if unable to allocate the resource

Since:

3.1

destroyResource

public abstract void destroyResource(Object previouslyCreatedObject)

Undoes everything that was done by a previous call to create(...), given the object that was returned by create(...).

Parameters:

previouslyCreatedObject - an object that was returned by an equal descriptor in a previous call to createResource(...).

Since:

3.1