Is it possible to prevent signal from propagating to other QML?
Example:
//Base.qml
Item {
signal backClicked()
//handles the back button
}
//Test1.qml
Base {
onBackClicked: console.log("BACK FROM TEST1")
}
//Test2.qml
Test1 {
onBackClicked: console.log("BACK FROM TEST2")
}
When i click the back button the output is the following:
"BACK FROM TEST1"
"BACK FROM TEST2"
Is it possible to decide when to propagate the backClickedSignal() to Test2?
Related
Using Qt Quick Controls 2, you can create a "traditional" menu bar like this:
ApplicationWindow {
id: window
width: 320
height: 260
visible: true
menuBar: MenuBar {
Menu {
title: qsTr("&File")
Action { text: qsTr("&New...") }
Action { text: qsTr("&Open...") }
Action { text: qsTr("&Save") }
Action { text: qsTr("Save &As...") }
MenuSeparator { }
Action { text: qsTr("&Quit") }
}
Menu {
title: qsTr("&Edit")
Action { text: qsTr("Cu&t") }
Action { text: qsTr("&Copy") }
Action { text: qsTr("&Paste") }
}
Menu {
title: qsTr("&Help")
Action { text: qsTr("&About") }
}
}
}
This works ok, but when the user presses on a menu and then drag the mouse while pressed, on the menus are not hovered. In order to hover over the menus, the mouse cannot be in a pressed state (using Qt Widgets https://doc.qt.io/qt-5/qtwidgets-mainwindows-menus-example.html this is not needed).
Is there a way to make the MenuBar, hover over items while the mouse is pressed?
When you did through this doc
https://doc.qt.io/qt-5/qml-qtquick-controls2-action.html
You then go to this doc and have high hopes when reading about "hoverEnabled"
https://doc.qt.io/qt-5/qml-qtquick-controls2-toolbutton-members.html
You really need these two signals entered() exited() from a MouseArea.
https://doc.qt.io/qt-5/qml-qtquick-mousearea.html
The short hopeful hack is to see if the documentation is "just wrong" and somewhere deep in the class structure they declared a MouseArea for a button and you really do get entered() and exited().
How else would you be able to implement hoverEnabled()? The "widget" has to know the mouse entered and did not yet exit. They may well be consuming that, but you should be able to dig through the source and find child entity that you can connect to the signal of.
There is not an easy way.
The underlying issue is that MenuItem is implemented as a Button.
When you press a button and release on another button, none of them register a click.
However, on traditional menus, if you press an item and release on another one, the item that registers the release is triggered.
The public API offered by QtQuick Controls 2 does not seem to offer a way to easily change this. So to get what you want Isee the following solutions:
Use Qt.labs.platform to build your menus, these will be native menus so they should have the correct behavior. However it still in a preview state and i have not tested them.
Reimplement MenuItem. Since it is part of Qt Quick Controls 2 it is easy to reimplement your own MenuItem, see Qt documentation. However, you will have to use MouseArea to catch user inputs and force the behavior you want.
EDIT
The 2nd solution won't work. In Qt once an Item (or a QWidget) accepts a press event, it grabs the mouse until it is released. So reimplementing MenuItem and adding MouseArea to them won't help.
Knowing that it seems that the solution would to reproduce what QMenu is doing: You need to have a single Item responsible for handling mouse events. So you should not let each MenuItem handles mouse events individually. Instead you should handle mouse events at the Menu or MenuBar level, process the events and manually change the MenuItems.
At this point I do not know if it is easier to customize Menu and MenuItem or to jus write your own Menu from scratch.
I have ImageButton.qml which should change image when user holds the button.
import QtQuick 2.0
Image {
id: svg
property string idleImage
property string hoverImage
signal clicked
state: "idle"
source: state === "idle" ? idleImage : hoverImage
onSourceChanged: {
console.log("source = " + source)
}
MouseArea {
id: mouseArea
anchors.fill: parent
acceptedButtons: Qt.LeftButton
onPressedChanged: {
svg.state = pressed ? "hover" : "idle"
}
onClicked: svg.clicked()
}
}
But the image is not changed immediately. It's changed only when I hold the button for several seconds. When I press and release mouse button immediately I never see the hover image. onSourceChanged is executed immediately and outputs to console the right image source. This strange bug happens only when I use QQuickWidget. When I don't use widgets, but qml only everything works as expected.
I found the issue. I am using QOpenGLWidget in the MainWindow. And I called update method in paintGL.
void Workspace::paintGL() {
QOpenGLWidget::paintGL();
workspaceDrawer.draw();
update();
}
I replaced update call with a timer, running every 1000 / 60 milliseconds.
And the issue was gone. It's strange that it was reproduced only when a mouse button was pressed, otherwise everything was updated correctly.
I have search high and low in the documentation but have not found anything regarding this. Is there anyway that an QML element I have created can get notified if one of it's children needs to be redrawn due to changes to it. Will the item send a signal or an event that the parent can connect/listen to. Preferably it would be emitted when the item is marked "dirty" and should be rendered again, but a signal like onPropertyChange would work also.
Example
MyQmlItem {
Rectangle {
width: 50; height: 60
color: "blue"
Text {
text: "hello world"
}
}
}
If some code e.g changes the color of the Rectangle I would like the MyQmlItem to be notified about this change.
FWIIW i managed to find an acceptable solution to above. I added a boolean property "isDirty" to the MyQmlItem class, this emits a signal when it is set to true. Then each child needs to set this if it makes changes that needs redrawing, the QML above then becomes
MyQmlItem {
id: "topItem"
Rectangle {
width: 50; height: 60
color: "blue"
Text {
text: "hello world"
onTextChange: {
topItem.isDirty = true;
}
}
}
not perfect, but good enough
We have a fairly big QtQuick application, with a lot of modal dialogs. All of these modals share a consistent look and behaviour, and have leftButtons, rightButtons, a content and additional warning widgets. We use the following base class (PFDialog.qml):
Window {
property alias content: contentLayout.children
ColumnLayout {
id: contentLayout
}
}
and declare dialogs in the following way (main.qml):
Window {
visible: true
property var window: PFDialog {
content: Text { text: "Foobar" }
}
}
The problem is that when the application is closed, a segfault happens in the QQuickItem destructor. This segfault is hard to reproduce, but here is a surefire way of making it happen: with visual studio in debug mode, freed memory is filled with 0xDDDDDDD with triggers the segfault every time.
Full example application can be found here: https://github.com/wesen/testWindowCrash
The crash happens in QQuickItem::~QQuickItem:
for (int ii = 0; ii < d->changeListeners.count(); ++ii) {
QQuickAnchorsPrivate *anchor = d->changeListeners.at(ii).listener->anchorPrivate();
if (anchor)
anchor->clearItem(this);
}
The reason for this is that the content of our dialog (the Text item in the example above) is a QObject child of the main Window, but a visual child of the dialog window. When closing the application, the dialog window is destroyed first, and at the time the Text item is deleted, the dialog window (still registered as a changeListener) is stale.
Now my question is:
is this a QtQuick bug? Should the dialog deregister itself as a changeListener for its children when it is destroyed (I think it should)
is our property alias content: layout.children pattern correct, or is there a better way to do this? This also happens when declaring a default property alias.
For the sake of completeness, here is how we hotfix it in our application. When content changes, we reparent all the items to the layout item. A of elegance, as you will all agree.
function reparentTo(objects, newParent) {
for (var i = 0; i < objects.length; i++) {
qmlHelpers.qml_SetQObjectParent(objects[i], newParent)
}
}
onContentChanged: reparentTo(content, contentLayout)
I have had this problem lots of times, I don't think it is a bug, more like a design limitation. The more implicit behavior you get, the less control you have, leading to inappropriate orders of object destruction and access to dangling references.
There are numerous situations where this can happen "on its own" as you exceed the bounds of a trivial "by the book" qml application, but in your case it is you who's doing it.
If you want proper ownership, don't use this:
property var window: PFDialog {
content: Text { text: "Foobar" }
}
Instead use this:
property Window window: dlg // if you need to access it externally
PFDialog {
id: dlg
content: Text { text: "Foobar" }
}
Here is a good reason why:
property var item : Item {
Item {
Component.onCompleted: console.log(parent) // qml: QQuickItem(0x4ed720) - OK
}
}
// vs
property var item : Item {
property var i: Item {
Component.onCompleted: console.log(parent) // qml: null - BAD
}
}
A child is not the same as a property. Properties are still collected but they are not parented.
As for achieving the "dynamic content" thingie, I've had good results with ObjectModel:
Window {
property ObjectModel layout
ListView {
width: contentItem.childrenRect.width // expand to content size
height: contentItem.childrenRect.height
model: layout
interactive: false // don't flick
orientation: ListView.Vertical
}
}
Then:
PFDialog {
layout: ObjectModel {
Text { text: "Foobar" }
// other stuff
}
}
Lastly, for the sake of doing explicit cleanups before closing the application, on your main QML file you can implement a handler:
onClosing: {
if (!canExit) doCleanup()
close.accepted = true
}
This ensures the window will not be destroyed without doing the cleanup first.
Finally:
is our property alias content: layout.children pattern correct, or is
there a better way to do this? This also happens when declaring a
default property alias.
It wasn't last time I looked into it, but it was at least couple of years back. It would certainly be nice to have objects declared as children actually becoming children of some other object, but at the time this was not possible, and still may not be. Thus the need for the slightly more verbose solution involving the object model and the list view. If you investigate the matter and find something different, leave a comment to let me know.
I believe that you cannot declare a Window Object in a var. In my tests the SubWindow never open and sometimes broken on startup.
A Window can be declared inside an Item or inside another Window; in that case the inner Window will automatically become "transient for" the outer Window
See: http://doc.qt.io/qt-5/qml-qtquick-window-window.html
Modify your code to this:
Window {
visible: true
PFDialog {
content: Text { text: "Foobar" }
}
}
In QtQuick 2 using the QtQuick Controls you can create complex desktop apps. However it seems to me that the entire UI must be declared and create all at once at the start of the app. Any parts that you don't want to use yet (for example the File->Open dialog) must still be created but they are hidden, like this:
ApplicationWindow {
FileDialog {
id: fileOpenDialog
visible: false
// ...
}
FileDialog {
id: fileSaveDialog
visible: false
// ...
}
// And so on for every window in your app and every piece of UI.
Now, this may be fine for simple apps, but for complex ones or apps with many dialogs surely this is a crazy thing to do? In the traditional QtWidgets model you would dynamically create your dialog when needed.
I know there are some workarounds for this, e.g. you can use a Loader or even create QML objects dynamically directly in javascript, but they are very ugly and you lose all the benefits of the nice QML syntax. Also you can't really "unload" the components. Well Loader claims you can but I tried it and my app crashed.
Is there an elegant solution to this problem? Or do I simply have to bite the bullet and create all the potential UI for my app at once and then hide most of it?
Note: this page has information about using Loaders to get around this, but as you can see it is not a very nice solution.
Edit 1 - Why is Loader suboptimal?
Ok, to show you why Loader is not really that pleasant, consider this example which starts some complex task and waits for a result. Suppose that - unlike all the trivial examples people usually give - the task has many inputs and several outputs.
This is the Loader solution:
Window {
Loader {
id: task
source: "ComplexTask.qml"
active: false
}
TextField {
id: input1
}
TextField {
id: output1
}
Button {
text: "Begin complex task"
onClicked: {
// Show the task.
if (task.active === false)
{
task.active = true;
// Connect completed signal if it hasn't been already.
task.item.taskCompleted.connect(onTaskCompleted)
}
view.item.input1 = input1.text;
// And several more lines of that...
}
}
}
function onTaskCompleted()
{
output1.text = view.item.output1
// And several more lines...
// This actually causes a crash in my code:
// view.active = false;
}
}
If I was doing it without Loader, I could have something like this:
Window {
ComplexTask {
id: task
taskInput1: input1.text
componentLoaded: false
onCompleted: componentLoaded = false
}
TextField {
id: input1
}
TextField {
id: output1
text: task.taskOutput1
}
Button {
text: "Begin complex task"
onClicked: task.componentLoaded = true
}
}
That is obviously way simpler. What I clearly want is some way for the ComplexTask to be loaded and have all its declarative relationships activated when componentLoaded is set to true, and then have the relationships disconnected and unload the component when componentLoaded is set to false. I'm pretty sure there is no way to make something like this in Qt currently.
Creating QML components from JS dynamically is just as ugly as creating widgets from C++ dynamically (if not less so, as it is actually more flexible). There is nothing ugly about it, you can implement your QML components in separate files, use every assistance Creator provides in their creation, and instantiate those components wherever you need them as much as you need them. It is far uglier to have everything hidden from the get go, it is also a lot heavier and it could not possibly anticipate everything that might happen as well dynamic component instantiation can.
Here is a minimalistic self-contained example, it doesn't even use a loader, since the dialog is locally available QML file.
Dialog.qml
Rectangle {
id: dialog
anchors.fill: parent
color: "lightblue"
property var target : null
Column {
TextField {
id: name
text: "new name"
}
Button {
text: "OK"
onClicked: {
if (target) target.text = name.text
dialog.destroy()
}
}
Button {
text: "Cancel"
onClicked: dialog.destroy()
}
}
}
main.qml
ApplicationWindow {
visible: true
width: 200
height: 200
Button {
id: button
text: "rename me"
width: 200
onClicked: {
var component = Qt.createComponent("Dialog.qml")
var obj = component.createObject(overlay)
obj.target = button
}
}
Item {
id: overlay
anchors.fill: parent
}
}
Also, the above example is very barebone and just for the sake of illustration, consider using a stack view, either your own implementation or the available since 5.1 stock StackView.
Here's a slight alternative to ddriver's answer that doesn't call Qt.createComponent() every time you create an instance of that component (which will be quite slow):
// Message dialog box component.
Component {
id: messageBoxFactory
MessageDialog {
}
}
// Create and show a new message box.
function showMessage(text, title, modal)
{
if (typeof modal === 'undefined')
modal = true;
// mainWindow is the parent. We can also specify initial property values.
var messageDialog = messageBoxFactory.createObject(mainWindow, {
text: text,
title: title,
visible: true,
modality: modal ? Qt.ApplicationModal : Qt.NonModal
} );
messageDialog.accepted.connect(messageDialog.destroy);
messageDialog.rejected.connect(messageDialog.destroy);
}
I think loading and unloading elements is not actual any more because every user have more than 2GB RAM.
And do you think your app can take more than even 512 MB ram? I doubt it.
You should load qml elements and don't unload them, no crashes will happens, just store all pointers and manipulate qml frames.
If you just keep all your QML elements in RAM and store their states, it will works faster and looks better.
Example is my project that developed in that way: https://youtube.com/watch?v=UTMOd2s9Vkk
I have made base frame that inherited by all windows. This frame does have methods hide/show and resetState. Base window does contains all child frames, so via signal/slots other frames show/hide next required frame.