Overview | Package | Class | Tree | Deprecated | Index | Help
PREV CLASS NEXT CLASS | FRAMES NO FRAMES
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD

## com.trolltech.qt.core
Class QTimer

    java.lang.Object
      com.trolltech.qt.internal.QSignalEmitterInternal
          com.trolltech.qt.QSignalEmitter
              com.trolltech.qt.QtJambiObject
                  com.trolltech.qt.core.QObject
                      com.trolltech.qt.core.QTimer

All Implemented Interfaces:
  QtJambiInterface

    public class QTimer

extends QObject

The QTimer class provides repetitive and single-shot timers. The QTimer class provides a high-level programming interface for timers. To use it, create a QTimer, connect its `timeout()` signal to the appropriate slots, and call `start()`. From then on it will emit the `timeout()` signal at constant intervals.

Example for a one second (1000 millisecond) timer (from the Analog Clock example):
The following code example is written in c++.

        QTimer *timer = new QTimer(this);

        connect(timer, SIGNAL(timeout()), this, SLOT(update()));

        timer->start(1000);

From then on, the `update()` slot is called every second.

You can set a timer to time out only once by calling setSingleShot(true). You can also use the static `QTimer::singleShot()` function to call a slot after a specified interval:

            QTimer.singleShot(200, this, "updateCaption()");

In multithreaded applications, you can use QTimer in any thread that has an event loop. To start an event loop from a non-GUI thread, use QThread::exec(). Qt uses the the timer's thread affinity to determine which thread will emit the `timeout()` signal. Because of this, you must start and stop the timer in its thread; it is not possible to start a timer from another thread.

As a special case, a QTimer with a timeout of 0 will time out as soon as all the events in the window system's event queue have been processed. This can be used to do heavy work while providing a snappy user interface:

            QTimer timer = new QTimer(this);

            timer.timeout.connect(this, "processOneThing()");

            timer.start();

`processOneThing()` will from then on be called repeatedly. It should be written in such a way that it always returns quickly (typically after processing one data item) so that Qt can deliver events to widgets and stop the timer as soon as it has done all its work. This is the traditional way of implementing heavy work in GUI applications; multithreading is now becoming available on more and more platforms, and we expect that zero-millisecond QTimers will gradually be replaced by QThreads.

Note that QTimer's accuracy depends on the underlying operating system and hardware. Most platforms support an accuracy of 1 millisecond, but Windows 98 supports only 55. If Qt is unable to deliver the requested number of timer clicks, it will silently discard some.

An alternative to using QTimer is to call `QObject::startTimer()` for your object and reimplement the `QObject::timerEvent()` event handler in your class (which must inherit `QObject`). The disadvantage is that `timerEvent()` does not support such high-level features as single-shot timers or signals.

Another alternative to using QTimer is to use `QBasicTimer`. It is typically less cumbersome than using `QObject::startTimer()` directly. See Timers for an overview of all three approaches.

Some operating systems limit the number of timers that may be used; Qt tries to work around these limitations.

See also:
  `QBasicTimer`, `QTimerEvent`, `QObject::timerEvent()`, Timers, Analog Clock Example, and Wiggly Example.

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
`com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal`

Field Summary
`QSignalEmitter.Signal0` | `timeout`

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

Constructor Summary
`QTimer()` Constructs a timer with the given `parent`.
`QTimer(QObject parent)` Constructs a timer with the given `parent`.

Method Summary
`int` | `interval()` This property holds the timeout interval in milliseconds.
`boolean` | `isActive()` This boolean property is true if the timer is running; otherwise false.
`boolean` | `isSingleShot()` This property holds whether the timer is a single-shot timer.
`void` | `setInterval(int msec)` This property holds the timeout interval in milliseconds.
`void` | `setSingleShot(boolean singleShot)` This property holds whether the timer is a single-shot timer.
`static void` | `singleShot(int msec, QObject obj, java.lang.String method)` This static function calls a slot after a given time interval.
`void` | `start()` Starts or restarts the timer with the timeout specified in `interval`.
`void` | `start(int msec)` Starts or restarts the timer with a timeout interval of `msec` milliseconds.
`void` | `stop()` Stops the timer.
`int` | `timerId()` Returns the ID of the timer if the timer is running; otherwise returns -1.

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
`__qt_signalInitialization`

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`

Field Detail

### timeout

    public final QSignalEmitter.Signal0 timeout

Constructor Detail

### QTimer

    public QTimer()

  Constructs a timer with the given `parent`.

### QTimer

    public QTimer(QObject parent)

  Constructs a timer with the given `parent`.

Method Detail

### interval

    public final int interval()

  This property holds the timeout interval in milliseconds. The default value for this property is 0. A QTimer with a timeout interval of 0 will time out as soon as all the events in the window system's event queue have been processed.

  Setting the interval of an active timer changes its `timerId()`.

See also:
  `singleShot`.

### isActive

    public final boolean isActive()

  This boolean property is true if the timer is running; otherwise false.

### isSingleShot

    public final boolean isSingleShot()

  This property holds whether the timer is a single-shot timer. A single-shot timer fires only once, non-single-shot timers fire every `interval` milliseconds.

See also:
  `interval`, and `singleShot()`.

### setInterval

    public final void setInterval(int msec)

  This property holds the timeout interval in milliseconds. The default value for this property is 0. A QTimer with a timeout interval of 0 will time out as soon as all the events in the window system's event queue have been processed.

  Setting the interval of an active timer changes its `timerId()`.

See also:
  `singleShot`.

### setSingleShot

    public final void setSingleShot(boolean singleShot)

  This property holds whether the timer is a single-shot timer. A single-shot timer fires only once, non-single-shot timers fire every `interval` milliseconds.

See also:
  `interval`, and `singleShot()`.

### start

    public final void start()

  Starts or restarts the timer with the timeout specified in `interval`.

  If `singleShot` is true, the timer will be activated only once.

### start

    public final void start(int msec)

  Starts or restarts the timer with a timeout interval of `msec` milliseconds.

### stop

    public final void stop()

  Stops the timer.

See also:
  `start()`.

### timerId

    public final int timerId()

  Returns the ID of the timer if the timer is running; otherwise returns -1.

### singleShot

    public static void singleShot(int msec,
                                  QObject obj,
                                  java.lang.String method)

  This static function calls a slot after a given time interval.

  It is very convenient to use this function because you do not need to bother with a QObject.timerEvent() or create a local QTimer object.

  Example:

          #include <QApplication>
          #include <QTimer>

          int main(int argc, char *argv[])
          {
              QApplication app(argc, argv);
              QTimer::singleShot(600000, &app, SLOT(quit()));
              ...
              return app.exec();
          }

  This sample program automatically terminates after 10 minutes (600,000 milliseconds).

  The `obj` is the receiving object and the `member` is the slot. The time interval is `msec` milliseconds.

Overview | Package | Class | Tree | Deprecated | Index | Help
PREV CLASS NEXT CLASS | FRAMES NO FRAMES
SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD