Class QPixmapCache

  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.gui.QPixmapCache
All Implemented Interfaces:

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
Field Summary
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
Constructor Summary
          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
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


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

Method Detail


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:


public static void clear()
Removes all pixmaps from the cache.


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:


public static void remove(java.lang.String key)
Removes the pixmap associated with key from the cache.


public static void setCacheLimit(int arg__1)
Sets the cache limit to n kilobytes.

The default setting is 1024 kilobytes.

See also:


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.