com.trolltech.qt.gui
Class QPixmapCache

java.lang.Object
  com.trolltech.qt.internal.QSignalEmitterInternal
      com.trolltech.qt.QSignalEmitter
          com.trolltech.qt.QtJambiObject
              com.trolltech.qt.gui.QPixmapCache

All Implemented Interfaces:

QtJambiInterface

public class QPixmapCache
extends QtJambiObject

The QPixmapCache class provides an application-wide cache for pixmaps. This class is a tool for optimized drawing with QPixmap. You can use it to store temporary pixmaps that are expensive to generate without using more storage space than cacheLimit(). Use insert() to insert pixmaps, find() to find them, and clear() to empty the cache.

QPixmapCache contains no member data, only static functions to access the global pixmap cache. It creates an internal QCache object for caching the pixmaps.

The cache associates a pixmap with a string (key). If two pixmaps are inserted into the cache using equal keys, then the last pixmap will hide the first pixmap. The QHash and QCache classes do exactly the same.

The cache becomes full when the total size of all pixmaps in the cache exceeds cacheLimit(). The initial cache limit is 1024 KB (1 MB); it is changed with setCacheLimit(). A pixmap takes roughly (width * height * depth)/8 bytes of memory.

The Qt Quarterly article Optimizing with QPixmapCache explains how to use QPixmapCache to speed up applications by caching the results of painting.

See also:

QCache, and QPixmap.

Nested Class Summary

Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter

QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9

Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal

Field Summary

Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

currentSender

Constructor Summary

QPixmapCache()
This is an overloaded method provided for convenience.

Method Summary

static int	cacheLimit() Returns the cache limit (in kilobytes).
static void	clear() Removes all pixmaps from the cache.
static boolean	find(java.lang.String key, QPixmap pm) Looks for a cached pixmap associated with the key in the cache.
static boolean	insert(java.lang.String key, QPixmap arg__2) Inserts a copy of the pixmap pm associated with the key into the cache.
static void	remove(java.lang.String key) Removes the pixmap associated with key from the cache.
static void	setCacheLimit(int arg__1) Sets the cache limit to n kilobytes.

Methods inherited from class com.trolltech.qt.QtJambiObject

dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr

Methods inherited from class com.trolltech.qt.QSignalEmitter

blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread

Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal

__qt_signalInitialization

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.trolltech.qt.QtJambiInterface

disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership

Constructor Detail

QPixmapCache

public QPixmapCache()

This is an overloaded method provided for convenience.

Method Detail

cacheLimit

public static int cacheLimit()

Returns the cache limit (in kilobytes).

The default cache limit is 2048 KB for Embedded, 10240 KB for Desktops.

See also:

setCacheLimit().

clear

public static void clear()

Removes all pixmaps from the cache.

insert

public static boolean insert(java.lang.String key,
                             QPixmap arg__2)

Inserts a copy of the pixmap pm associated with the key into the cache.

All pixmaps inserted by the Qt library have a key starting with "$qt", so your own pixmap keys should never begin "$qt".

When a pixmap is inserted and the cache is about to exceed its limit, it removes pixmaps until there is enough room for the pixmap to be inserted.

The oldest pixmaps (least recently accessed in the cache) are deleted when more space is needed.

The function returns true if the object was inserted into the cache; otherwise it returns false.

See also:

setCacheLimit().

remove

public static void remove(java.lang.String key)

Removes the pixmap associated with key from the cache.

setCacheLimit

public static void setCacheLimit(int arg__1)

Sets the cache limit to n kilobytes.

The default setting is 1024 kilobytes.

See also:

cacheLimit().

find

public static boolean find(java.lang.String key,
                           QPixmap pm)

Looks for a cached pixmap associated with the key in the cache. If the pixmap is found, the function sets pm to that pixmap and returns true; otherwise it leaves pm alone and returns false.