QML TreeView with custom delegate

oYASo · 15 Jan 2025, 14:12

Hi!

I'm trying to work with QML TreeView in Qt 6.8, but I'm having issues and can't make progress.
I want to create a hierarchy like the one shown in the screenshot, which includes:

an expand/collapse indicator
an icon
text
the number of items (for root nodes) or the size (for leaf nodes)

To start, I'm trying to solve a simple problem: aligning the size value to the right edge. However, any attempts to use anchors result in the entire list shifting somewhere, and I can't fix it.

The second problem is: how can I add an image?

Does anyone have examples of using TreeView with custom delegates? I can customize them perfectly for ListView, but I can't figure out how they work with TreeView.

Thanks for any advice!

Right now my code looks like this:

import QtQuick
import QtQuick.Controls
import Qt.labs.qmlmodels

Item {
    id: root
    width: 260
    height: 700

    TreeView {
        id: treeView
        anchors.fill: parent

        model: assetModel
        selectionModel: ItemSelectionModel {
            model: treeView.model
        }

        delegate: DelegateChooser {
            id: viewDelegate

            DelegateChoice {
                id: nameDelegateChoice
                column: 0
                delegate: TreeViewDelegate {
                    id: nameDelegate
                    implicitWidth: 150
                    background: Rectangle {
                        id: backgroundRectangle
                        color: "transparent"
                    }
                    contentItem: Row {
                        id: row
                        Image {
                            source: "../../images/svg-folder.svg"
                            width: 20
                            height: 20
                        }

                        Label {
                            text: model.display
                            color: "white"
                            font.pixelSize: 14
                            font.family: "Roboto Medium"
                        }
                    }
                }
            }
            DelegateChoice {
                id: sizeDelegateChoice
                column: 1
                delegate: TreeViewDelegate {
                    id: treeViewDelegate
                    background: Rectangle {
                        id: backgroundRectangle2
                        color: "transparent"
                    }
                    contentItem: Row {
                        id: row2
                        Label {
                            text: model.display
                            color: "white"
                            font.pixelSize: 14
                            font.family: "Roboto Medium"
                        }
                    }
                }
            }
        }
    }
}

Model:

#include "AssetModel.hpp"
#include <QVariantList>
#include "AssetItem.hpp"

AssetModel::AssetModel(QObject *parent)
    : QAbstractItemModel{parent}
    , m_rootItem(std::make_unique<AssetItem>("RootDir", AssetItem::Type::Directory))
{
    setupModelData();
}

AssetModel::~AssetModel() = default;

QVariant AssetModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid()) {
        return QVariant();
    }

    AssetItem *item = static_cast<AssetItem *>(index.internalPointer());
    if (role == Qt::DisplayRole) {
        return item->data(index.column());
    }

    return QVariant();
}

Qt::ItemFlags AssetModel::flags(const QModelIndex &index) const
{
    if (!index.isValid()) {
        return Qt::NoItemFlags;
    }

    return Qt::ItemIsSelectable | Qt::ItemIsEnabled;
}

QVariant AssetModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    return orientation == Qt::Horizontal && role == Qt::DisplayRole ? m_rootItem->data(section)
                                                                    : QVariant{};
}

QModelIndex AssetModel::index(int row, int column, const QModelIndex &parent) const
{
    if (!hasIndex(row, column, parent)) {
        return QModelIndex();
    }

    AssetItem *parentItem = parent.isValid() ? static_cast<AssetItem *>(parent.internalPointer())
                                             : m_rootItem.get();
    AssetItem *childItem = parentItem->child(row);

    return childItem ? createIndex(row, column, childItem) : QModelIndex();
}

QModelIndex AssetModel::parent(const QModelIndex &index) const
{
    if (!index.isValid()) {
        return QModelIndex();
    }

    AssetItem *childItem = static_cast<AssetItem *>(index.internalPointer());
    AssetItem *parentItem = childItem->parentItem();

    if (parentItem == m_rootItem.get()) {
        return QModelIndex();
    }

    return createIndex(parentItem->row(), 0, parentItem);
}

int AssetModel::rowCount(const QModelIndex &parent) const
{
    AssetItem *parentItem = parent.isValid() ? static_cast<AssetItem *>(parent.internalPointer())
                                             : m_rootItem.get();
    return parentItem->childCount();
}

int AssetModel::columnCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent)
    return 2; // Columns: name and size
}

// void AssetModel::setupModelData(const QList<QStringView> &lines, AssetItem *parent)
void AssetModel::setupModelData()
{
    // Example
    auto dir1 = std::make_unique<AssetItem>("Uploads", AssetItem::Type::Directory, m_rootItem.get());
    dir1->appendChild(
        std::make_unique<AssetItem>("logo.png", AssetItem::Type::File, dir1.get(), 1024));
    dir1->appendChild(
        std::make_unique<AssetItem>("Arial.ttf", AssetItem::Type::File, dir1.get(), 4332523));
    dir1->appendChild(
        std::make_unique<AssetItem>("Hello.zip", AssetItem::Type::File, dir1.get(), 3245452));
    dir1->appendChild(
        std::make_unique<AssetItem>("Intro.mp3", AssetItem::Type::File, dir1.get(), 53245132));
    dir1->appendChild(
        std::make_unique<AssetItem>("mem.gif", AssetItem::Type::File, dir1.get(), 35353));
    dir1->appendChild(
        std::make_unique<AssetItem>("File.xml", AssetItem::Type::File, dir1.get(), 77332));

    auto dir2 = std::make_unique<AssetItem>("Assets", AssetItem::Type::Directory, m_rootItem.get());
    dir2->appendChild(
        std::make_unique<AssetItem>("avatar_1.png", AssetItem::Type::File, dir2.get(), 43245));
    dir2->appendChild(
        std::make_unique<AssetItem>("avatar_2.png", AssetItem::Type::File, dir2.get(), 73412));

    m_rootItem->appendChild(std::move(dir1));
    m_rootItem->appendChild(std::move(dir2));
}

And TreeView looks like this:

oYASo · wrote on 21 Jan 2025, 13:49

Hi!

Thank you for your responses!

Unfortunately, the documentation for TreeView is not very detailed, and examples are quite scarce. I followed your advice and dug deeper into how the delegate works for TreeView. As a result, I managed to achieve exactly what I needed, as shown in the original screenshot.

To help others understand this topic more easily, I’ll share my code below.

Key ideas:

The entire view layout can be customized using the delegate. There’s no need to come up with complex solutions like DelegateChooser, which I had been trying earlier.
You can use the column and row variables to determine which row or column is being processed.
As mentioned earlier, to align text, you should use horizontalAlignment.
You need to align the row yourself (make indents depending on the nesting).

import QtQuick
import QtQuick.Controls
import Qt5Compat.GraphicalEffects

Item {
    id: root
    width: 260
    height: 700

    TreeView {
        id: treeView
        anchors.fill: parent
        anchors.margins: 10
        clip: true

        model: assetModel
        selectionModel: ItemSelectionModel {
            model: treeView.model
        }

        delegate: Item {
            implicitWidth: column === 0 ? root.width * 2/3 - padding * 2 : root.width * 1/3 - padding * 2
            implicitHeight: label.implicitHeight * 1.5

            readonly property real indentation: 20
            readonly property real padding: 5

            // Assigned to by TreeView:
            required property TreeView treeView
            required property bool isTreeNode
            required property bool expanded
            required property int hasChildren
            required property int depth
            required property int row
            required property int column
            required property bool current

            property Animation indicatorAnimation: NumberAnimation {
                target: indicator
                property: "rotation"
                from: expanded ? 0 : 90
                to: expanded ? 90 : 0
                duration: 100
                easing.type: Easing.OutQuart
            }
            TableView.onPooled: indicatorAnimation.complete()
            TableView.onReused: if (current) indicatorAnimation.start()
            onExpandedChanged: indicator.rotation = expanded ? 90 : 0

            Rectangle {
                id: background
                anchors.fill: parent
                color: row === treeView.currentRow ? "#0085F8" : "transparent"
            }

            Label {
                id: indicator
                x: padding + (depth * indentation) + 5
                anchors.verticalCenter: parent.verticalCenter
                visible: isTreeNode && hasChildren
                text: "▶"
                color: "white"

                TapHandler {
                    onSingleTapped: {
                        let index = treeView.index(row, column)
                        treeView.selectionModel.setCurrentIndex(index, ItemSelectionModel.NoUpdate)
                        treeView.toggleExpanded(row)
                    }
                }
            }

            Image {
                id: image
                x: (isTreeNode ? (depth + 1) * indentation : 0)
                anchors.verticalCenter: parent.verticalCenter
                width: 13
                height: 13
                source:  hasChildren ? "../../images/svg-folder.svg" : "../../images/svg-file.svg"
                visible: column === 0 ? true : false

                ColorOverlay {
                    source: image
                    anchors.fill: image
                    color: "white"
                }
            }

            Label {
                id: label
                x: image.x + image.width + 5
                anchors.verticalCenter: parent.verticalCenter
                width: parent.width - padding - x
                clip: true
                text: model.display
                color: column === 0 ? "white" : "#ABABAB"
                font.pixelSize: column === 0 ? 14 : 10
                horizontalAlignment: isTreeNode ? Text.AlignLeft : Text.AlignRight
                rightPadding: 10
                font.family: "Roboto Medium"
            }
        }

        MouseArea {
            id: menuMouseArea
            anchors.fill: parent
            acceptedButtons: Qt.RightButton

            Connections {
                target: menuMouseArea
                onClicked: {
                    menu.open()
                    menu.x = menuMouseArea.mouseX
                    menu.y = menuMouseArea.mouseY
                }
            }
        }
    }

    Menu {
        id: menu
        width: 150
        leftPadding: 5
        font.family: "Roboto Medium"

        palette.window: "#1f1f1f"
        palette.text: "white"
        palette.windowText: "white"
        palette.light: "#898989"

        MenuItem {
            text: "Rename"
            icon.source: "../../images/svg-edit.svg"
            icon.width: 14
            icon.height: 14
        }
        MenuItem {
            text: "Delete"
            icon.source: "../../images/svg-trash.svg"
            icon.width: 14
            icon.height: 14
        }
    }
}

Now it looks like this:

Thank you all!

Bob64 · 15 Jan 2025, 17:40

@oYASo said in QML TreeView with custom delegate:

To start, I'm trying to solve a simple problem: aligning the size value to the right edge. However, any attempts to use anchors result in the entire list shifting somewhere, and I can't fix it.

I found it a bit tricky to unpick what it is you are asking. It looks like the issue mentioned above is not illustrated in the code you provided - correct?

So the main issue you discuss is the image one. I am not saying that what you have done is incorrect but in my projects I have always included images in my resources rather than trying to find them as relative paths. My source: settings then look something like this:

Image {
    source: "qrc:///icons/arrow-up.svg"
}

This corresponds to a line like this in my qml.qrc:

    <file>icons/arrow-up.svg</file>

The actual image file in my project is at the path specified above, relative to the location of the qml.qrc.

Something looks odd to me in your DelegateChooser code, though it might be because I don't have much experience with using this component. I thought that the DelegateChooser was supposed to define a role name for the role that will be used to select the choice, and that the DelegateChoices would each specify a roleValue to determine which value of the role they should correspond to. I'm also not entirely sure that you are using columns correctly in your model and view but again it could just be my ignorance.

To make progress, I would simplify this as much as possible - perhaps forget about the delegate choice in the first instance, and focus on getting the image displaying.

oYASo · B Bob64 15 Jan 2025, 14:12

@Bob64 Thank you for your response, and sorry for the unclear explanation of my issue.

The first problem I’m facing is how to align content to the left or right in a TreeView column. The first screenshot in my post shows how I’d like it to look, while the second screenshot shows the current state. On the second screenshot, you can see that the file size is aligned to the left, but I need it to be aligned to the right.

I tried solving this issue by using alignment in the model, specifically with the TextAlignmentRole, but it seems like this doesn’t work.

I also attempted to achieve this by aligning the contentItem in the delegate, but this didn’t work either.

So, my initial question is: how can I align the second column in a TreeView to the right?

Bob64 · wrote on 16 Jan 2025, 10:46

OK, thanks for the clarification.

It seems like this should not be too difficult. If I understand correctly now, the tree has two columns and second delegate choice is for the second column.

I would probably start by removing the Row from the content item of the second column as it doesn't seem to be serving much purpose and will get in the way of using other layout mechanisms like anchors. I would replace it with an Item that fills the available width. You should then be able to anchor the text to the right of the containing item.

GrecKo · wrote on 16 Jan 2025, 13:18

TreeView and TreeViewDelegate ignores the TextAlignmentRole.

Getting rid of the Row and using the Label with horizontalAlignment should do the trick:

delegate: TreeViewDelegate {
    background: null // there's no point in using a Rectangle with a transparent background
    contentItem: Label {
        text: model.display
        horizontalAlignment: Text.AlignRight
        color: "white"
        font.pixelSize: 14
        font.family: "Roboto Medium"
    }
}

oYASo · wrote on 21 Jan 2025, 13:49

Hi!