signalprobe-item.rst

SignalProbe Item

..  cpp:class:: SignalProbe

    Watches signals from other items.

..  cpp:namespace:: SignalProbe

Inherits:	:qml:item:`Component`
Properties:	:cpp:member:`condition`, :cpp:member:`count`, :cpp:member:`signal`
Methods:	:cpp:func:`clear()`, :cpp:func:`connect()`
Signals:	:cpp:func:`triggered()`

Detailed Description

..  cpp:namespace:: SignalProbe

SignalProbe can be used to watch signals of other items. A typical use-case is a counter for asynchronous events:

import qst 1.0
import QtQml 2.0 as QtQml

Testcase {
    QtQml.Timer {
        id : timer
        interval: 5
        periodic: true
    }

    SignalProbe {
        id: probe
        signal: timer.triggered
    }

    function run() {
        Qst.compare(probe.count, 0, "Timer triggered too early");
        timer.start();
        Qst.wait(50);
        timer.stop();
        Qst.verify(probe.count >= 10, "Timer triggered only "
            + probe.count + " times");
    }

The following example shows, how SignalProbe can be used, to attach to a signal that is not directly accessible:

import qst 1.0

Testcase {
    property var pinProbe : PinProbe {
        // properties
        // ...

        // Can attach directly to the valueChanged() signal.
        onValueChanged: {
            Qst.info("pin value is " + pinProbe.value)
        }
    }
}

import qst 1.0

BaseTestcase {
    // Cannot attach directly to pinProbe's valueChanged() signal.
    // Use SignalProbe instead.
    SignalProbe {
        signal: pinProbe.valueChanged
        onTriggered: {
            Qst.info("pin value is " + pinProbe.value)
        }
    }
}

Properties

..  cpp:member:: bool condition

    :default: true

    A guard for :cpp:member:`signal`. When ``true``, incoming signals increment
    the counter and emit :cpp:func:`triggered()`. When ``false``, the incoming
    signal is ignored.

..  cpp:member:: int count

    Counts how many times the signal has fired with respect to
    :cpp:member:`condition`.

..  cpp:member:: Signal signal

    A signal of another item to attach to during the creation stage.

Methods

..  cpp:function:: void clear()

    Resets :cpp:member:`count` to 0 but leaves the signal connection and the
    condition untouched.

..  cpp:function:: void connect(signalHandler)

    Connects the :cpp:func:`triggered()` signal to a `signalHandler` of another
    item. This makes ``SignalProbe`` look like a QML signal for the other item.

    Example::

        DurationConstraint {
            from: SignalProbe { signal: someItem.someSignal }
            to: someOtherSignal
        }

    In this example, ``DurationConstraint`` tries to connect ``SignalProbe`` to
    itself by calling :cpp:func:`connect()`. It doesn't know that
    ``SignalProbe`` is an item and not a plain QML signal.

Signals

..  cpp:function:: void triggered()

    Emitted when :cpp:member:`signal` is triggered while :cpp:member:`condition`
    is true.