I am trying to pass log data to my QML front end, one line at a time, and have it append to the end of a TextArea. I've considered several approaches. The following is the most promising. I have created a QAbstractListModel (in Python) and pass this model into a repeater where it arrives as a single item (rowCount =1) which I append to the TextArea using the line
text: terminal_text.text + display
This works but I get this warning everytime the text is updated.
file://.../TextArea.qml:728:9: QML QQuickTextEdit*: Binding loop detected for property "text"
See below for the code of the repeater.
Repeater {
model: TerminalFeed { }
delegate: TextArea {
id: terminal_text
font.family: "Courier"
width: parent.width
height: parent.height
readOnly: true
selectByMouse: true
wrapMode: TextEdit.NoWrap
horizontalScrollBarPolicy: Qt.ScrollBarAsNeeded
verticalScrollBarPolicy: Qt.ScrollBarAsNeeded
text: terminal_text.text + display
}
}
How can I stop this happening? Alternatively does anyone have a better way of achieving the same result?
Technically, that is indeed a binding loop because text is dependent on its own value. If QML didn't detect it and break it, an infinite loop of updating would result.
Instead of using a binding, you can do something like this:
Repeater {
model: TerminalFeed { }
delegate: TextArea {
id: terminal_text
font.family: "Courier"
width: parent.width
height: parent.height
readOnly: true
selectByMouse: true
wrapMode: TextEdit.NoWrap
horizontalScrollBarPolicy: Qt.ScrollBarAsNeeded
verticalScrollBarPolicy: Qt.ScrollBarAsNeeded
onDisplayChanged: {
text = text + display;
}
}
}
With the original binding approach, it will try and update whenever either display or text changes. With this approach, it will only try and update whenever display changes – which is what you really want.
I had a similar problem where I wanted to show logged data in a QML window.
I use the insert() method, which is inherited from QML TextField. The insertion position is the length of the TextArea.
TextArea {
id: outputTextArea
}
Component.onCompleted: {
data = "dummyString"
outputTextArea.insert(outputTextArea.length, data)
}
Related
Here's my QML view:
// Imports ommitted
Item {
id: paymentMethods
required property PaymentMethodsModel model
ColumnLayout {
anchors.fill: parent;
Text {
text: "Payment methods";
}
ListView {
Layout.fillHeight: true
Layout.fillWidth: true
model: paymentMethods.model
delegate: PaymentMethods.Item { }
}
ToolBar { }
}
}
The problem is, it looks like this:
I think it's because the delegate doesn't specify width, because if I do this:
delegate: PaymentMethods.Item {
width: parent.width
onPmSaved: {
ListView.view.model.rename(index, newName)
}
}
It looks much better:
The problem is, when I do edits that reorder the items, I get this error:
qrc:/PaymentMethods.qml:32: TypeError: Cannot read property 'width' of null
Is there a good way to set a QML ListView's delegate's width to full parent's width?
From the ListView documentation:
Delegates are instantiated as needed and may be destroyed at any time. As such, state should never be stored in a delegate. Delegates are usually parented to ListView's contentItem, but typically depending on whether it's visible in the view or not, the parent can change, and sometimes be null. Because of that, binding to the parent's properties from within the delegate is not recommended. If you want the delegate to fill out the width of the ListView, consider using one of the following approaches instead:
ListView {
id: listView
// ...
delegate: Item {
// Incorrect.
width: parent.width
// Correct.
width: listView.width
width: ListView.view.width
// ...
}
}
In the transition of the reordering, the item does not have a parent, so the error indicates it, a possible solution is to set the width of the item depending on whether it has a parent or not.
width: parent ? parent.width : 40 // default value
I need to insert elements in a ListView inside another ListView (via JS code inside my QML file) but when I try to access the inner ListView I get the error :
TypeError: Cannot call method 'insert' of undefined
Here is an example code to show my problem :
Item{
id:list
width: parent.width-210
height: parent.height
x:105
Component{
id:listDelegate
Item {
id:elem
height: 100
width: parent.width
Item{
id:titre_liste
height: 50
width: parent.width
Text{
anchors.left: parent.left
color:"white"
text:titre_txt
font.pixelSize: 25
font.bold: false
}
}
Item{
id:listInList
width: parent.width-100
height: parent.height
Component{
id:listInListDelegate
Item{
id:element_liste
height: parent.height
width: parent.width/5
Text{
anchors.left: parent.left
color:"white"
text:element_txt
font.pixelSize: 25
font.bold: true
}
}
}
ListView {
id: viewin
anchors.fill: parent
model: ListModel{
id:listModel_in
}
delegate: listInListDelegate
}
}
}
}
ListView {
id: viewglobal
anchors.fill: parent
model: ListModel{
id:listModel
}
delegate: listDelegate
}
}
And here is my JS code, at the end of the QML file :
function addItem(){
var i;
var numListe = -1;
var liste = "titre"
var item = "item"
for(i = 0;i<listModel.count;i++)
{
if(listModel.get(i).titre_txt === liste)
{
numListe = i;
}
}
if(numListe === -1)//if the list doesn't exist
{
listModel.append({titre_txt:liste});
numListe = listModel.count-1;
}
listModel.get(numListe).listModel_in.insert(0,{element_txt:item});
}
The error come from the last line of the JS code, when I try to insert a new element in the inner list. I verified that the value of "numListe" is 0 so it is not just a problem of wrong index.
How can I add elements to the inner list ?
There is a lot of stuff wrong with that code.
For starters - it is a mess, which is a very bad idea for someone who is obviously new at this stuff. Keep it clean - that's always a good idea regardless of your level of expertise.
listModel_in is an id and as such cannot be accessed outside of the delegate component.
That object however happens to be bound to the view's model property, so as long as the model doesn't change, you can access listModel_in via the model property. However, the view itself doesn't look like it is the delegate root object, so you have to interface it, for example by using an alias.
However, the inner model doesn't exist in the outer model, it only exists in the outer model's delegate item.
So you cannot possibly get it from listModel. You can get it from the viewglobal view, however ListView doesn't provide access by index. So you will have to set currentIndex for every index and use currentItem.
So it will look like this:
viewglobal.currentItem.modelAlias.insert(0,{element_txt:item});
But it should go without saying, you are putting data in the GUI layer, which is conceptually wrong. But it gets worse than conceptually wrong - you might not be aware of this, but ListView only creates items that it needs to show, meaning that it creates and destroys delegates as necessary. Meaning if your item falls out of view, it will be destroyed, and when it comes back into view, a new one will be created, and all the data you had in the model of the old delegate item will be lost. The view should never store data, just show it.
The inner model should be inside the outer model. However, last time I checked, QMLs ListModel didn't support model nesting, neither using declarative nor imperative syntax. If you want to nest models, I have provided a generic object model QML type you can use.
Lets imaging project for desktop which contains only one QML file:
import QtQuick 2.4
import QtQuick.Window 2.2
Window {
visible: true
width: 500
height: 500
ListModel {
id: myModel
ListElement {
color: "red"
text: "some interesting information"
}
ListElement {
color: "blue"
text: "not so interesting information"
}
ListElement {
color: "green"
text: "and some more information"
}
}
ListView {
anchors.fill: parent
interactive: false
model: myModel
delegate: Rectangle {
width: parent.width
height: 30
color: model.color
TextEdit {
anchors.centerIn: parent
text: model.text
selectByMouse: true
}
}
}
}
With the selectByMouse property of TextEdit set to true I can select text in it. But how can I select text in multiple delegates at the same time? In multiple TextEdits? Is it even possible?
Since the other answers seem incomplete or don't answer what I believe VALOD9 was asking: "can you select text across multiple delegates as though their TextEdits are one element?"
This is not inherently possible, but can be crafted in QML with a lot of manual tracking of mouse presses and movement.
It could be accomplished by placing MouseArea over your ListView and delegates that each contain DropAreas. To track your text selection clicks/drags across your delegates, you could use an invisible MouseArea.drag.target that triggers the delegate DropAreas' onEntered and onPositionChanged events. Based on all this data, you can use TextEdit.positionAt() with your mouse coordinate results to get where your selections start and end, and use TextEdit.select() to programmatically select the text in each delegate. Since you are programmatically selecting text, your TextEdits would need to have selectByMouse: false.
You will need to store any necessary selection data in your model since you shouldn't store state in delegates in case they are removed from the ListView from automatic caching. You would then use this data to recreate the selection when they are re-loaded from cache using Component.OnCompleted. To do selection operations like copy, you could iterate over your model and pick up the saved selection data (especially if you save the selected text to the model using TextEdit.selectedText).
This would allow many TextEdit-based delegates to act as though they are one when selecting text across any of them.
You can set persistentSelection to true and each of your TextEdit will keep the text selected (http://doc.qt.io/qt-5/qml-qtquick-textedit.html#persistentSelection-prop)
What I need to do: I need to create a chat window using a ListView in QML that stores the chat-messages. I set listView.positionViewAtEnd() in order to follow the last messages. I disable positionViewAtEnd when I scroll upwards such that I can read the past messages without jumping at the end every time I receive a new message.
The problem: After scrolling up, every time I receive a new message it jumps at the beginning of list. To solve that I manage to store the contentY of the list and reset it every time onCountChanged handler is called (see the code below):
ListView {
id: messagesList
model: contact? contact.messages: []
delegate: delegate
anchors.fill: parent
anchors.bottomMargin: 20
height: parent.height
anchors.margins: 10
property int currentContentY
onMovementEnded: {
currentContentY = contentY
}
onCountChanged: {
contentY = currentContentY
}
onContentYChanged: {
console.log(".....contentY: " + contentY)
}
}
The problem is that even though I set the last contentY I had, before the model was changed, the list still jumps a bit (several pixels, not at the end or beginning) and it doesn't jump always. And when I go to the top of the list and print the contentY I get negative values. Theoretically, contentY at the beginning of the list should be 0.
Can somebody tell me what is going wrong? Or maybe suggest another solution to create my message list?
Than you in advance! :)
One possible solution schould be insert ListView into Flickable and disable interactive flag for ListView
Flickable {
id: fparent
anchors.fill: parent
anchors.bottomMargin: 20
anchors.margins: 10
interactive: true
clip: true
flickableDirection: Flickable.VerticalFlick
contentHeight: messagesList.height
ListView {
id: messagesList
width: parent.width
height: childrenRect.height
clip: true
model: contact? contact.messages: []
delegate: delegate
interactive: false
onCountChanged: {
fparents.returnToBounds();
}
}
}
Why not use onCountChanged slot in order to set the ListView at the end ?
onCountChanged: {
messagesList.positionViewAtEnd()
}
I'm going crazy. I have a ListView inside a ScrollView, hooked up to a model that inherits QAbstractListModel. When objects are added to the model, the ListView shows them using a delegate. So far, so good.
But I really want the view to stay scrolled to the bottom (like a chat window), and I'm having a very difficult time making that happen. Here is the relevant QML code:
Rectangle {
ScrollView {
[anchor stuff]
ListView {
id: messageList
model: textMessageFiltered
delegate: messageDelegate
}
}
TextField {
id: messageEditor
[anchor stuff]
onAccepted: {
controller.sendTextMessage(text)
text = ""
/* This works. */
//messageList.positionViewAtEnd();
}
}
Component {
id: messageDelegate
Rectangle {
anchors.left: parent.left
anchors.right: parent.right
color: "white"
height: nameText.height + 4
Text {
id: nameText
wrapMode: Text.Wrap
text: "<b>" + authorName + " (" + authorId + ")</b> " + message
[anchor stuff]
}
ListView.onAdd: {
console.log("This prints just fine!")
messageList.positionViewAtEnd()
}
}
}
}
The really strange thing, is that messageList.positionViewAtEnd() (at the end of the file) actually jumps it to the beginning. Without the call, the view stays where it is, even as new entries appear in the list. And indeed, if you look at the Qt documentation for the ListView.positionViewAtEnd(), it says:
Positions the view at the beginning or end, taking into account ...
Is that a silly error in the documentation, or what? I've tried everything I can think of to make this work, particularly the positionViewAtIndex() method and using highlighters to force the scroll to happen. But nothing works. Note the /* This works. */ comment in the source code above. When that is enabled, it works totally fine! (except of course, it jumps to the ListView.count()-2 index, instead of the end of the list)
Does anyone have any idea what might be wrong here? Any examples I could try to prove that there's a terrible, terrible bug in QML?
I'm using Qt 5.3.1 with QtQuick 2.0 (or 2.1 or 2.2 fail too). I've tried many, many other configurations and code as well, so please ask if you need more info. I've completely exhausted my google-fu.
Thanks!
Edit 1
While the accepted answer does solve the above problem, it involves adding the Component.onCompleted to the delegate. This seems to cause problems when you scroll the list, because (I believe) the delegates are added to the view when you scroll up, causing the onCompleted trigger to be called even if the model item isn't new. This is highly undesirable. In fact, the application is freezing when I try to scroll up and then add new elements to the list.
It seems like I need a model.onAdd() signal instead of using the existence of a delegate instance to trigger the scroll. Any ideas?
Edit 2
And how does this NOT work?
ListView {
id: messageList
model: textMessageFiltered
delegate: messageDelegate
onCountChanged: {
console.log("This prints properly.")
messageList.positionViewAtEnd()
}
}
The text "This prints properly" prints, so why doesn't it position? In fact, it appears to reset the position to the top. So I tried positionViewAtBeginning(), but that did the same thing.
I'm totally stumped. It feels like a bug.
You need to set the currentIndex as well.
testme.qml
import QtQuick 2.2
import QtQuick.Controls 1.1
import QtQuick.Window 2.0
ApplicationWindow {
title: qsTr("Hello World")
width: 300
height: 240
ScrollView {
anchors.fill: parent
ListView {
anchors.fill: parent
id: messageList
model: messageModel
delegate: Text { text: mytextrole }
highlight: Rectangle { color: "red" }
highlightMoveDuration: 0
onCountChanged: {
var newIndex = count - 1 // last index
positionViewAtEnd()
currentIndex = newIndex
}
}
}
ListModel {
id: messageModel
ListElement { mytextrole: "Dog"; }
ListElement { mytextrole: "Cat"; }
}
Timer {
property int counter: 0
running: true
interval: 500
repeat: true
onTriggered: {
messageModel.append({"mytextrole": "Line" + (counter++)})
}
}
}
There is still some jumping to the first element and jumping back down for a fraction of a second.
There is a note in documentation:
Note: methods should only be called after the Component has completed. To position the view at startup, this method should be called by Component.onCompleted.
Change your ListView.onAdd: to
Component.onCompleted: {
console.log("This prints just fine!")
messageList.positionViewAtEnd()
}
And it works well.
In your case, the ListView emits add signal before the new delegate is created and completed. The ListView is still working on something behind the scene, so positionViewAtEnd cannot work as expected. And /* This works. */ because it is called after the new delegate is completed. However, don't assume this always works. Simply follow the note, call positionViewAtEnd in Component.onCompleted, in documentation.