Different delegates for QML ListView - qt

Question

I would like to know if it's possible to use (several) different delegates for a QML ListView.
Depending on the individual object in the ListView model, I would like to visualize the objects with different delegates.
This piece of code explains what I want to achieve:
main.qml
import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Window 2.2
import QtQuick.Dialogs 1.2
ApplicationWindow {
title: qsTr("Hello World")
width: 640
height: 480
visible: true
ListModel {
id: contactsModel
ListElement {
name: "Bill Smith"
position: "Engineer"
}
ListElement {
name: "John Brown"
position: "Engineer"
}
ListElement {
name: "Sam Wise"
position: "Manager"
}
}
ListView {
id: contactsView
anchors.left: parent.left
anchors.top: parent.top
width: parent.width
height: parent.height
orientation: Qt.Vertical
spacing: 10
model: contactsModel
delegate: {
if (position == "Engineer") return Employee; //<--- depending on condition, load Contact{}
else if (position == "Manager") return Manager; //<--- depending on condition, load Person{}
}
}
}
Employee.qml (One possible Component which I would like to use as a delegate)
import QtQuick 2.4
Rectangle{
width: 200
height: 50
color: ListView.isCurrentItem ? "#003366" : "#585858"
border.color: "gray"
border.width: 1
Text{
anchors.centerIn: parent
color: "white"
text: name
}
}
Manager.qml (other Component I would like to use as a delegate)
import QtQuick 2.4
Rectangle{
width: 200
height: 50
color: "red"
border.color: "blue"
border.width: 1
Text{
anchors.centerIn: parent
color: "white"
text: name
}
}
I would appreciate any advice!
Thanks!

Answer 1

I've had the same problem, the Qt documentation is providing a pretty good answer: http://doc.qt.io/qt-5/qml-qtquick-loader.html#using-a-loader-within-a-view-delegate
The easiest solution is an inline Component with a Loader to set a source file:
ListView {
id: contactsView
anchors.left: parent.left
anchors.top: parent.top
width: parent.width
height: parent.height
orientation: Qt.Vertical
spacing: 10
model: contactsModel
delegate: Component {
Loader {
source: switch(position) {
case "Engineer": return "Employee.qml"
case "Manager": return "Manager.qml"
}
}
}
}
Any attempt to use Loader.srcComponent will result in missing any variable from the model (including index). The only way for the variables to be present is the children Component to be inside the main Component, but then only one can be present, so it is useless.

Answer 2

I believe it would be better to implement one base delegate for all kind of position which loads concrete implementation depending on position or any other data properties using Loader
BaseDelegate {
property var position
Loader {
sourceComponent: {
switch(position) {
case "Engineer": return engineerDelegate
}
}
}
Component {
id: engineerDelegate
Rectangle {
Text { }
}
}
}

Answer 3

I implemented it as follow:
ListView {
id: iranCitiesList
model: sampleModel
delegate: Loader {
height: childrenRect.height
width: parent.width
sourceComponent: {
switch(itemType) {
case "image" :
return imageDel;
case "video":
return videoDel;
}
}
}
ImageDelegate { id: imageDel }
VideoDelegate { id: videoDel }
}
ImageDelegate.qml
Component {
Image { /*...*/ }
}
VideoDelegate.qml
Component {
Item { /*....*/ }
}
Last note, check width and height of delegates. In my case, I had to set width and height of my delegate in Loader again.
Good luck - Mousavi

Answer 4

The simplest way to do this now is using DelegateChooser. This also allows you to edit the properties of the delegates, which is something that is more difficult to do with Loader!
Example inspired from the docs:
import QtQuick 2.14
import QtQuick.Controls 2.14
import Qt.labs.qmlmodels 1.0
ListView {
width: 640; height: 480
ListModel {
id: contactsModel
ListElement {
name: "Bill Smith"
position: "Engineer"
}
ListElement {
name: "John Brown"
position: "Engineer"
}
ListElement {
name: "Sam Wise"
position: "Manager"
}
}
DelegateChooser {
id: chooser
role: "position"
DelegateChoice { roleValue: "Manager"; Manager { ... } }
DelegateChoice { roleValue: "Employee"; Employee { ... } }
}
model: contractsModel
delegate: chooser
}

Answer 5

Sure, it's possible. ListView.delegate is a kind of pointer to a Component which will draw the items so you can change it.
For example:
Employee { id: delegateEmployee }
Manager { id: delegateManager}
...
ListView {
property string position
delegate: position == "Engineer" ? delegateEmployee : delegateManager
}

Answer 6

As far as you have only two types, the following code is as easy to maintain as easy to understand:
delegate: Item {
Employee { visible = position === "Engineer" }
Manager { visible = position === "Manager" }
}
In case the number of types will grow, it is not a suitable solution for it easily leads to an hell of if statement.

Answer 7

Because position is either "Manager" or "Engineer" and the delegates are saved in Manager.qml or Engineer.qml we can use a clever expression for Loader.source:
Loader {
source: position + ".qml"
}
Here's the full source:
import QtQuick
import QtQuick.Controls
Page {
ListModel {
id: contactsModel
ListElement { name: "Bill Smith"; position: "Engineer" }
ListElement { name: "John Brown"; position: "Engineer" }
ListElement { name: "Sam Wise"; position: "Manager" }
}
ListView {
id: listView
anchors.fill: parent
model: contactsModel
delegate: Loader {
width: ListView.view.width
source: position + ".qml"
}
}
}
//Engineer.qml
import QtQuick
import QtQuick.Controls
Rectangle {
property bool isCurrentItem: listView.currentIndex === index
height: 50
color: isCurrentItem ? "#0033cc" : "#585858"
border.color: "gray"
border.width: 1
Text {
anchors.centerIn: parent
color: "white"
text: name
}
}
//Manager.qml
import QtQuick
import QtQuick.Controls
Rectangle {
property bool isCurrentItem: listView.currentIndex === index
height: 50
color: isCurrentItem ? "#cc3300" : "#661100"
border.color: "blue"
border.width: 1
Text {
anchors.centerIn: parent
color: "white"
text: name
}
}
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