I'm trying to create a QML item, defined in C++, that would intercept frames from a QML Camera before they are displayed by a VideoOutput. Something like:
Window {
Camera {
id: camera
}
MyFrameinterceptor {
id: myprocessing
source: camera.mediaObject
}
VideoOutput {
id: feedback
source: myprocessing
}
}
According to this comment, the mediaObject property of a Camera item can be used to access the C++ part of the Camera.
However, when I try to access the mediaObject from QML, e.g. with
Text {
text: qsTr(camera.mediaObject.objectName)
}
I get a TypeError: Cannot read property 'objectName' of undefined
When I try to use the camera.mediaObject property from C++, I get similar messages letting me think that mediaObject is undefined, uninitialized or not existing.
I'm new to Qt, so I may miss something really stupid, like starting the camera or what not... But I have the same problem with a MediaPlayer item
How can I access the mediaObject of a QML Camera from C++?
I tripped into this a couple of times as well, I resolved it like so:
QObject * obj = rootview->rootObject()->findChild<QObject *>("camera");
QVariant mediaObject = obj->property("mediaObject");
QCamera * camera = qvariant_cast<QCamera *>(mediaObject);
I then use a QVideoRendererControl to assign a subclass of QAbstractVideoSurface to process frames.
Related
I have a application and I want make a little animation for it.
I did a qml file and used QQuickWidget to open and show it in my display. Now a I want make iteration between c++ and QML. I want, for example, when a function in c++ is called, a ball move in my display. But I could not make a connection between c++ and qml.
Every help is welcome.
A little part of my code:
c++
QQuickWidget *quickWidget = new QQuickWidget;
quickWidget->setSource(QUrl("qrc:/QML/main.qml"));
auto rootObject = quickWidget->rootObject();
// Connect C++ signal to QML slot
connect(this, SIGNAL(cppSignal()), rootObject, SLOT(qmlSlot()));
emit cppSignal();
QML
Rectangle {
id: tela
visible: true
width: 715
height: 77
color: '#E8E8E8'
// NumberAnimation {
// running: true
// target: bolinha
// property: "x"
// duration: 1000
// to: 600
// }
function qmlSlot() {
bolinha.visible= enabled
animBolinha.start();
}
}
enter image description here
What I can do to solve it?
I am not sure if you can call a QML method from C++ code as you did.
The recommended way from QT documentation is:
All QML methods are exposed to the meta-object system. As the functions are exposed to meta-object system, you can use QMetaObject::invokeMethod(), to invoke the QML function.
Probably in your case, you should call as said below (not tested).
auto rootObject = quickWidget->rootObject();
QMetaObject::invokeMethod(rootObject, "qmlSlot");
Look documentation (search for Invoking QML Methods)
As said in documentation, you can use Q_ARG to pass the arguments and Q_RETURN_ARG for receiving return arguments.
As most people familiar with QML know, there is no builtin "refresh" functionality in QML Image.
I would like to create a new QML type, say RefreshableImage to alleviate this problem without resorting to changing the source, which I feel is an ugly hack, as it bleeds into all layers of the Model-View relationship and this switching behaviour is unnatural. Additionally, setting a different source on an Image breaks any binding that may have been set (which is really the core of the problem: I want an updateable image that maintains its binding, and is isolated to QML). I understand I'll need to call some signal to actually refresh the image, that's fine.
I have trouble finding documentation on a way to extend Qt's own Image so that I can force it to reload its source. I would like to avoid writing a complete component that mostly badly replicates Image to add one function. Is there a way to extend a builtin component like I have in mind?
Minor notes:
due to external circumstances, I'm limited to Qt 5.5.
We use as source a UUID of the underlying image object which is used by an QQuickImageProvider to get the actual QImage. Hence I don't want to change this when updating an image.
You could create a RefreshableImage type that hides the ugly source changing from you.
There's a simple way of doing it by introducing a new property for the source :
import QtQuick 2.0
Image {
id: root
property string refreshableSource
source: refreshableSource
function refresh() {
source = "";
source = Qt.binding(function() { return refreshableSource });
}
}
You have to use it like that : RefreshableImage { refreshableSource: "image.jpg" }.
If you want to still use source as a property, you could do it with some aliases shenanigans. Since aliases are only activated once a component has been fully initialized, you can overwrite the source property of Image but still be able to access the underlying one.
import QtQuick 2.0
Image {
id: root
property alias actualUnderlyingSource: root.source //this refers to Image.source and not the newly created source alias
property alias source: root.refreshableSource
property string refreshableSource
actualUnderlyingSource: refreshableSource
function refresh() {
actualUnderlyingSource = "";
actualUnderlyingSource = Qt.binding(function() { return refreshableSource });
}
}
You could then use it like so RefreshableImage { source: "image.jpg" }, this will in fact modify the refreshableSource property
A rough skeleton for directly using QImage from a model with a custom item
class DirectImage : public QQuickPaintedItem
{
Q_OBJECT
Q_PROPERTY(QImage image READ image WRITE setImage NOTIFY imageChanged)
public:
void paint(QPainter *painer);
void setImage(const QImage &image);
};
void DirectImage::paint(QPainter *painter)
{
painter->drawImage(m_image.scaled(width(), height()):
}
void DirectImage::setImage(const QImage &image)
{
m_image = image;
emit imageChanged();
setImplicitWidth(image.width());
setImplicitHeight(image.height());
update();
}
Registered via
qmlRegisterType<DirectImage>("MyElements", 1, 0, "RefreshableImage");
Use via
import MyElements 1.0
// ...
RefreshableImage {
image: model.image
}
The model just returns the QImage when asked for the image role, emits the dataChanged() signal with the image role whenever the image changes.
If the image needs to be generated on demand, the model can first return an empty image or a placeholder image and emit the dataChanged() signal when the actual content is available.
Basically my situation is like this:
I've got a class that extends QQuickView and that exposes certain objects from C++ to QML by setting context properties. The views that are shown are created from QML and are all different istances of the same custom made component; new views are created when certain events occur, and when that happens the existing views should show the objects that were initially assigned to them in the C++ side, and the new ones should show the things assigned to them.
So, in the C++ side I've got something like this:
WindowManager::WindowManager(QQuickView *parent) :
QQuickView(parent)
{
// Setting the source file to use
this->setSource(QUrl("qrc:/qml/main.qml"));
// Exposing the istance of this class to QML for later use
this->rootContext()->setContextProperty("qquickView", this);
// Calling the method that will create dynamically a new view that will be child of main.qml; the parameter is not important, just a random number to start with
this->prepareNewView(3)
this->showFullScreen();
}
WindowManager::prepareNewView(int stuffId)
{
MyDatabase db;
// Getting something to show in QML from somewhere based on the parameter received
SomeStuff stuff = db.getStuff(stuffId)
// Exposing the object I need to show in QML
this->rootContext()->setContextProperty("someStuff", stuff);
QObject *object = this->rootObject();
// Here I'm invoking a function from main.qml that will add a new view dynamically
QMetaObject::invokeMethod(object, "addView");
}
Now, in the QML side I've got a main file like this:
// main.qml
Rectangle {
id: mainWindow
width: 1000
height: 1000
// This function adds a component to mainWindow
function addView()
{
// Creating the component from my custom made component
var component = Qt.createComponent("MyComponent.qml");
// Creating an istance of that component as a child of mainWindow
var newView = component.createObject(mainWindow);
// ... Now I would be doing something with this new view, like connecting signals to slots and such
}
}
Then I've got my custom component, which is the view that will be created dynamically:
// MyComponent.qml
Rectangle {
id: customComponent
// Here I would be using the object I exposed from the C++ side
x: someStuff.x
y: someStuff.y
width: someStuff.width
height: someStuff.height
// Here I'm creating a MouseArea so that clicking this component will cause the creation of another view, that will have to show diffrent things since the parameter I'm passing should be different from the starting parameter passed in the constructor of WindowManager
MouseArea {
anchors.fill: parent
onClicked: qquickView.prepareNewView(Math.random())
}
}
Now, with everything as it is, at first it will show "the stuff" with id 3, that was exposed as a context property of the main context.
But then, if I click on the MouseArea, assuming that an id other than 3 will be passed, a new context property with the same name will be exposed, causing the override of the old property. This means that the first view will now show "the stuff" just exposed, not "the stuff" based from the stuffId equals to 3, while what I need is the first view to keep showing what it was supposed to show ("the stuff" with id = 3), and any other view that will come later the things corresponding to their ids.
This happens because I'm defining a property in the context that is common to every component, while I should be defining a property that is visible ONLY by the new istance of the component that is being created dynamically. But how do I do that?
In the documentation I read that it's possibile to create a component directly from C++ and defining the context that it should use... something like this (snippet taken from here):
QQmlEngine engine;
QStringListModel modelData;
QQmlContext *context = new QQmlContext(engine.rootContext());
context->setContextProperty("myModel", &modelData);
QQmlComponent component(&engine);
component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl());
QObject *window = component.create(context);
I think that this would work for what I intend to do. Whenever I create a new view from C++ (caused by the click on the MouseArea) I create a new context with "someStuff" as its property, so that each view has its own "stuff"... but I need to have access to the newly created view from QML, because after I create it in the addView() function inside main.qml I access the view in order to do certain thins (not important what exactly), and if I create the istance of the component from C++ I don't know how to access it from QML... is there a way maybe to pass the component from C++ to QML in order to access it?
I'm out of ideas on how to resolve this or to find another way to have dynamically created views with custom contents all visible at the same time... any suggestions are appreciated.
I actually found out that it is possible (and easy) to directly pass a component created in C++ to QML.
So right now, I modified the code pretty much like this:
WindowManager::prepareNewView(int stuffId)
{
MyDatabase db;
// Getting something to show in QML from somewhere based on the parameter received
SomeStuff stuff = db.getStuff(stuffId)
// Creating the new context, based on the global one
QQmlContext *context = new QQmlContext(this->rootContext());
// Exposing the object I need to show in QML to the new context
context ->setContextProperty("someStuff", stuff);
// Creating the component
QQmlComponent component(this->engine(), QUrl("qrc:/qml/MyComponent.qml"));
// Creating the istance of the new component using the new context
QQuickItem *newView = qobject_cast<QQuickItem*>(component.create(context));
// Getting the root component (the Rectangle with it mainWindow)
QObject *object = this->rootObject();
// Manually setting the new component as a child of mainWIndow
newView->setParentItem(qobject_cast<QQuickItem*>(object));
// Invoking the QML that will connect the events of the new window, while passing the component created above as QVariant
QMetaObject::invokeMethod(object, "addView", Q_ARG(QVariant, QVariant::fromValue(newView)));
}
In QML the function in the main.qml is now like this:
// Function called from C++; the param "newView" is the last component added
function addView(newView)
{
// ... Here I would use the new view to connect signals to slots and such as if I created "newView" directly in QML
}
So I managed not to change the code too much after all.
I think you can pass your component instance (QObject) by setting an object as a context property as you did in your code.
class ViewInstance : public QObject
{
Q_OBJECT
public:
Q_INVOKABLE QObject* getCurrentViewInstance() {
...
QObject *window = component.create(context);
return window;
}
};
int main(int argc, char *argv[]) {
...
QQuickView view;
ViewInstance data;
view.rootContext()->setContextProperty("viewInstance", &data);
}
Then, in your qml, you can get the component instance by calling viewInstance.getCurrentViewInstance(). Hope this helps.
I'm facing a big problem that it's taking a lot of time to be fixed because I don't know the cause and how to fix it. The problem is really simple: I have an example QML component defined as:
Rectangle {
id: rect
property bool test: myclass.testproperty
Rectangle {
width: 50
height: 50
visible: parent.test
}
}
and I connected a MouseArea onClicked signal to do this:
test = !test
so I switch the value of the boolean variable. To push the value from C++ to QML and from QML to C++ Q_PROPERTY with READ, WRITE and NOTIFY signals, I used this
Binding {
target: myclass
property: "testproperty"
value: rect.test
}
everything works fine until I click on the mouseArea and so I push the changes via the binding. After that, every time I try to set a new property value from C++ I don't see any change in QML, like if the binding is destroyed. But if I try to click on the MouseArea I still call the setTestProperty method of the C++ class. Basically, it goes out of sync the C++ -> QML way. Why? I can't find the problem, the signal is emitted because QSignalSpy gives me 1 as count of emitted times after using
emit this->testPropertyChanged(newvalue)
EDIT
here an example: basically here we're using a QString property with the same exact signals. The only thing that changes is that instead of using a Rectangle QML element and binding to a own property, I'm using a TextInput element
TextInput {
id: mytext
text: myclass.testproperty
}
Binding {
target: myclass
property: "testproperty"
value: mytext.text
}
There is no problem here. It is a standard QML bindings behaviour. When you change some QML Widget's property in JavaScript code, then all declarative bindings to it will be terminated. It is your choice to use declarative binding or update values manually in JS code of event handlers.
EDIT
Rectangle {
id: rect
// Establishing initial value for 'test' property via QML binding
property bool test: myclass.testproperty
// Manual update of 'test' property when binding will be broken
Connections {
target: myclass
onTestpropertyChanged: {
rect.test = xxx
}
}
}
I'm trying to use a qml-grid view in my code. I'm trying to couple it with my C++ code.
I've dynamically created a list view model and passed across the qml file. It works fine.
However, I'm facing trouble when I want to connect a Qml signal to Qt/c++ code. I've handled mouseArea in my Qml-rectangle and emitting a signal from there.
I'm trying to connect to the signal as follows:
QDeclarativeView *pQMLContainer = NULL;
TempWidget *pTemp = new TempWidget();
pQMLContainer = new QDeclarativeView(pTemp);
pQMLContainer->setResizeMode(QDeclarativeView::SizeRootObjectToView);
pQMLContainer->rootContext()->setContextProperty("imgModel", createModel() );
pQMLContainer->setSource(QUrl("../Temp/qml/gridview-example.qml"));
QObject *rootObject = dynamic_cast<QObject*>pQMLContainer->rootObject();
QObject::connect(rootObject, SIGNAL(keyPressed()), pTemp, SLOT(onKeyPressed()));
When the connect statement runs, I get an error: cannot connect to "null" object.
On debugging, I found I could never get "rootObject" as a valid pointer.
Where am I going wrong?
Thanks
Can you try this ? (it is example code from Qt Docs)
QObject *item = pQMLContainer->rootObject();
QObject::connect(item, SIGNAL(keyPressed()),
pTemp, SLOT(onKeyPressed()));
The code is pretty much straight:
in .cpp file:
ui->declarativeView->setSource(QUrl("qrc:/Resources/main.qml"));
QGraphicsObject *obj = ui->declarativeView->rootObject();
connect ( obj, SIGNAL(clicked()), this, SLOT(itemClicked()));
and QML File:
import Qt 4.7
Rectangle {
width: 100
height: 100
id: rect
signal clicked
Text {
text: "Hello World"
anchors.centerIn: parent
}
MouseArea {
anchors.fill: parent
onClicked: {
rect.clicked();
}
}
}
one more thing, check the location of your qml file, it should be accessible to the binary.
Perhaps you should use qobject_cast instead of dynamic_cast? See e.g. question
dynamic_cast returns NULL but it shouldn't
QGraphicsObject is a QObject so no cast should be required. If your compiler complains, try adding #include <QGraphicsObject>.
Just casting without the compiler knowing the classes is asking for trouble. (Especially as there is multiple inheritance involved.)
I could finally get this working. I'm not sure if this is the real solution to the problem, but finally this got it working:
I was setting the qml path as a relative path to my working folder. And yes the path was indeed correct, as I could see the qml and its contents. I just happened to change the qml path from relative to the working folder to relative to "qrc" as:
pQMLContainer->setSource(QUrl("qrc:/gridview-example.qml"));
instead of:
pQMLContainer->setSource(QUrl("../Temp/qml/gridview-example.qml"));
and it started working. I'm not sure if I had to add the qml to the qrc (I've just started using qml).
Thanks everyone for your support!
Mots