Class QFutureWatcher

  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QObject
                  extended by com.trolltech.qt.core.QFutureWatcherBase
                      extended by com.trolltech.qt.core.QFutureWatcher
All Implemented Interfaces:

public class QFutureWatcher
extends QFutureWatcherBase

The QFutureWatcher class allows monitoring a QFuture using signals and slots. QFutureWatcher provides information and notifications about a QFuture. Use the setFuture() function to start watching a particular QFuture. The future() function returns the future set with setFuture().

For convenience, several of QFuture's functions are also available in QFutureWatcher: progressValue(), progressMinimum(), progressMaximum(), progressText(), isStarted(), isFinished(), isRunning(), isCanceled(), isPaused(), waitForFinished(), result(), and resultAt(). The cancel(), setPaused(), pause(), resume(), and togglePaused() functions are slots in QFutureWatcher.

Status changes are reported via the started(), finished(), canceled(), paused(), resumed(), resultReadyAt(), and resultsReadyAt() signals. Progress information is provided from the progressRangeChanged(), void progressValueChanged(), and progressTextChanged() signals.

Throttling control is provided by the setPendingResultsLimit() function. When the number of pending resultReadyAt() or resultsReadyAt() signals exceeds the limit, the computation represented by the future will be throttled automatically. The computation will resume once the number of pending signals drops below the limit.

Example: Starting a computation and getting a slot callback when it's finished:

    // Instantiate the objects and connect to the finished signal.
    MyClass myObject = new MyClass();
    QFutureWatcher<Integer> watcher = new QFutureWatcher<Integer>();
    watcher.finished.connect(myObject, "handleFinished()");

    // Start the computation.
    QFuture<Integer> future =, method, arg1, arg2);
Be aware that not all asynchronous computations can be canceled or paused. For example, the future returned by QtConcurrent::run() cannot be canceled; but the future returned by QtConcurrent::mappedReduced() can.

QFutureWatcher<void> is specialized to not contain any of the result fetching functions. Any QFuture<T> can be watched by a QFutureWatcher<void> as well. This is useful if only status or progress information is needed; not the actual result data.

See also:
QFuture, and Qt Concurrent.

Nested Class Summary
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, 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.core.QFutureWatcherBase
canceled, finished, paused, progressRangeChanged, progressTextChanged, progressValueChanged, resultReadyAt, resultsReadyAt, resumed, started
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
Constructor Summary
          Constructs a new QFutureWatcher with the given parent.
QFutureWatcher(QObject _parent)
          Constructs a new QFutureWatcher with the given parent.
Method Summary
 QFuture future()
          Returns the watched future.
 java.lang.Object result()
          Returns the first result in the future().
 java.lang.Object resultAt(int index)
          Returns the result at index in the future().
 void setFuture(QFuture future)
          Starts watching the given future.
Methods inherited from class com.trolltech.qt.core.QObject
childEvent, children, connectSlotsByName, customEvent, disposeLater, dumpObjectInfo, dumpObjectTree, dynamicPropertyNames, event, eventFilter, findChild, findChild, findChild, findChildren, findChildren, findChildren, findChildren, indexOfProperty, installEventFilter, isWidgetType, killTimer, moveToThread, objectName, parent, properties, property, removeEventFilter, setObjectName, setParent, setProperty, startTimer, timerEvent, toString, userProperty
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, wait, wait, wait
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership

Constructor Detail


public QFutureWatcher()
Constructs a new QFutureWatcher with the given parent.


public QFutureWatcher(QObject _parent)
Constructs a new QFutureWatcher with the given parent.

Method Detail


public final java.lang.Object result()
Returns the first result in the future(). If the result is not immediately available, this function will block and wait for the result to become available. This is a convenience method for calling resultAt(0).

See also:


public final java.lang.Object resultAt(int index)
Returns the result at index in the future(). If the result is not immediately available, this function will block and wait for the result to become available.

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public final void setFuture(QFuture future)
Starts watching the given future.

See also:


public final QFuture future()
Returns the watched future.

See also: