Hello,
i do not understand the behaviour of my compiled Qt-Quick-C++ application when
using
property var ctx: getContext("2d")
in a simple qml Canvas component. I do get run time errors
qrc:/NotWorkingRectangle.qml:7:5: QML Canvas: Unable to use getContext() at
this time, please wait for available: true
qrc:/NotWorkingRectangle.qml:16: TypeError: Type error
and nothing will be painted. If i use the same qml files with QML Scene tool
everything is painted as expected and no run time errors are shown. Do you have
any advice why? Minimal samples follow:
main.cpp:
-------------
#include <QApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
main.qml:
--------------
import QtQuick 2.3
import QtQuick.Controls 1.2
ApplicationWindow {
visible: true
width: 640
height: 480
NotWorkingRectangle {
}
}
NotWorkingRectangle.qml:
-----------------------------------
import QtQuick 2.3
import QtQuick.Controls 1.2
Rectangle {
anchors.fill: parent
Canvas {
property var ctx: getContext("2d")
anchors.fill: parent
onWidthChanged: { requestPaint() }
onPaint: { myPaint() }
function myPaint() {
ctx.strokeStyle = "black"
ctx.shadowBlur = 0
ctx.beginPath()
ctx.moveTo(0, 0)
ctx.lineTo(width/2, height/2)
ctx.stroke()
ctx.closePath()
}
}
}
In my real world component i have lots of painting functions and i do not want
to pass the ctx element every time i want to use it. I also do not want to call
getContext("2d") locally. I know it returns the same Object every next call but
it is just code i would like to spare.
Mit freundlichen Grüßen/ Best regards
Christoph Petzold
Mitarbeiter Abteilung Funktionelle Elektrostimulation
HASOMED GmbH
Paul-Ecke-Str. 1
39114 Magdeburg
Tel.: +49 391 62 30 112
Fax: +49 391 62 30 113
E Mail: christoph.petz...@hasomed.de
Web: www.hasomed.de
HRB 108418
UST IdNo DE 114 161 708
Steuernummer 102/111/09705
GF Dr. Peter Weber, Frank Schulze
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