TableView QML Type

Provides a table view of items provided by the model. More...

Import Statement: import QtQuick 2.12
Inherits:

Flickable

Properties

Attached Properties

Attached Signals

Methods

Detailed Description

A TableView has a model that defines the data to be displayed, and a delegate that defines how the data should be displayed.

TableView inherits Flickable. This means that while the model can have any number of rows and columns, only a subsection of the table is usually visible inside the viewport. As soon as you flick, new rows and columns enter the viewport, while old ones exit and are removed from the viewport. The rows and columns that move out are reused for building the rows and columns that move into the viewport. As such, the TableView support models of any size without affecting performance.

A TableView displays data from models created from built-in QML types such as ListModel and XmlListModel, which populates the first column only in a TableView. To create models with multiple columns, create a model in C++ that inherits QAbstractItemModel, and expose it to QML.

Example Usage

The following example shows how to create a model from C++ with multiple columns:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QAbstractTableModel>

class TableModel : public QAbstractTableModel
{
    Q_OBJECT

public:

    int rowCount(const QModelIndex & = QModelIndex()) const override
    {
        return 200;
    }

    int columnCount(const QModelIndex & = QModelIndex()) const override
    {
        return 200;
    }

    QVariant data(const QModelIndex &index, int role) const override
    {
        switch (role) {
            case Qt::DisplayRole:
                return QString("%1, %2").arg(index.column()).arg(index.row());
            default:
                break;
        }

        return QVariant();
    }

    QHash<int, QByteArray> roleNames() const override
    {
        return { {Qt::DisplayRole, "display"} };
    }
};

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qmlRegisterType<TableModel>("TableModel", 0, 1, "TableModel");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    return app.exec();
}

#include "main.moc"

And then how to use it from QML:

import QtQuick 2.12
import TableModel 0.1

TableView {
    anchors.fill: parent
    columnSpacing: 1
    rowSpacing: 1
    clip: true

    model: TableModel {}

    delegate: Rectangle {
        implicitWidth: 100
        implicitHeight: 50
        Text {
            text: display
        }
    }
}

Reusing items

TableView recycles delegate items by default, instead of instantiating from the delegate whenever new rows and columns are flicked into view. This can give a huge performance boost, depending on the complexity of the delegate.

When an item is flicked out, it moves to the reuse pool, which is an internal cache of unused items. When this happens, the TableView::pooled signal is emitted to inform the item about it. Likewise, when the item is moved back from the pool, the TableView::reused signal is emitted.

Any item properties that come from the model are updated when the item is reused. This includes index, row, and column, but also any model roles.

Note: Avoid storing any state inside a delegate. If you do, reset it manually on receiving the TableView::reused signal.

If an item has timers or animations, consider pausing them on receiving the TableView::pooled signal. That way you avoid using the CPU resources for items that are not visible. Likewise, if an item has resources that cannot be reused, they could be freed up.

If you don't want to reuse items or if the delegate cannot support it, you can set the reuseItems property to false.

Note: While an item is in the pool, it might still be alive and respond to connected signals and bindings.

The following example shows a delegate that animates a spinning rectangle. When it is pooled, the animation is temporarily paused:

Component {
    id: tableViewDelegate
    Rectangle {
        implicitWidth: 100
        implicitHeight: 50

        TableView.onPooled: rotationAnimation.pause()
        TableView.onReused: rotationAnimation.resume()

        Rectangle {
            id: rect
            anchors.centerIn: parent
            width: 40
            height: 5
            color: "green"

            RotationAnimation {
                id: rotationAnimation
                target: rect
                duration: (Math.random() * 2000) + 200
                from: 0
                to: 359
                running: true
                loops: Animation.Infinite
            }
        }
    }
}

Row heights and column widths

When a new column is flicked into view, TableView will determine its width by calling the columnWidthProvider function. TableView itself will never store row height or column width, as it's designed to support large models containing any number of rows and columns. Instead, it will ask the application whenever it needs to know.

TableView uses the largest implicitWidth among the items as the column width, unless the columnWidthProvider property is explicitly set. Once the column width is found, all other items in the same column are resized to this width, even if new items that are flicked in later have larger implicitWidth. Setting an explicit width on an item is ignored and overwritten.

Note: The calculated width of a column is discarded when it is flicked out of the viewport, and is recalculated if the column is flicked back in. The calculation is always based on the items that are visible when the column is flicked in. This means that it can end up different each time, depending on which row you're at when the column enters. You should therefore have the same implicitWidth for all items in a column, or set columnWidthProvider. The same logic applies for the row height calculation.

If you change the values that a rowHeightProvider or a columnWidthProvider return for rows and columns inside the viewport, you must call forceLayout. This informs TableView that it needs to use the provider functions again to recalculate and update the layout.

Note: The size of a row or column should be a whole number to avoid sub-pixel alignment of items.

The following example shows how to set a simple columnWidthProvider together with a timer that modifies the values the function returns. When the array is modified, forceLayout is called to let the changes take effect:

TableView {
    id: tableView

    property var columnWidths: [100, 50, 80, 150]
    columnWidthProvider: function (column) { return columnWidths[column] }

    Timer {
        running: true
        interval: 2000
        onTriggered: {
            tableView.columnWidths[2] = 150
            tableView.forceLayout();
        }
    }
}

Overlays and underlays

Tableview inherits Flickable. And when new items are instantiated from the delegate, it will parent them to the contentItem with a z value equal to 1. You can add your own items inside the Tableview, as child items of the Flickable. By controlling their z value, you can make them be on top of or underneath the table items.

Here is an example that shows how to add some text on top of the table, that moves together with the table as you flick:

TableView {
    id: tableView

    topMargin: header.implicitHeight

    Text {
        id: header
        text: "A table header"
    }
}

Property Documentation

columnSpacing : real

This property holds the spacing between the columns.

The default value is 0.


columnWidthProvider : var

This property can hold a function that returns the column width for each column in the model. When assigned, it is called whenever TableView needs to know the width of a specific column. The function takes one argument, column, for which the TableView needs to know the width.

Note: The width of a column must always be greater than 0.

See also rowHeightProvider and Row heights and column widths.


columns : int

This property holds the number of columns in the table. This is equal to the number of columns in the model. If the model is a list, columns will be 1.

This property is read only.


contentHeight : real

This property holds the height of the contentView, which is also the height of the table (including margins). As a TableView cannot always know the exact height of the table without loading all rows in the model, the contentHeight is usually an estimated height based on the rows it has seen so far. This estimate is recalculated whenever new rows are flicked into view, which means that the content height can change dynamically.

If you know up front what the height of the table will be, assign a value to contentHeight explicitly, to avoid unnecessary calculations and updates to the TableView.

See also contentWidth.


contentWidth : real

This property holds the width of the contentView, which is also the width of the table (including margins). As a TableView cannot always know the exact width of the table without loading all columns in the model, the contentWidth is usually an estimated width based on the columns it has seen so far. This estimate is recalculated whenever new columns are flicked into view, which means that the content width can change dynamically.

If you know up front what the width of the table will be, assign a value to contentWidth explicitly, to avoid unnecessary calculations and updates to the TableView.

See also contentHeight.


delegate : Component

The delegate provides a template defining each cell item instantiated by the view. The model index is exposed as an accessible index property. The same applies to row and column. Properties of the model are also available depending upon the type of Data Model.

A delegate should specify its size using implicitWidth and implicitHeight. The TableView lays out the items based on that information. Explicit width or height settings are ignored and overwritten.

Note: Delegates are instantiated as needed and may be destroyed at any time. They are also reused if the reuseItems property is set to true. You should therefore avoid storing state information in the delegates.

See also Row heights and column widths and Reusing items.


model : model

This property holds the model that provides data for the table.

The model provides the set of data that is used to create the items in the view. Models can be created directly in QML using ListModel, XmlListModel or ObjectModel, or provided by a custom C++ model class. If it is a C++ model, it must be a subclass of QAbstractItemModel or a simple list.

See also Data Models.


reuseItems : bool

This property holds whether or not items instantiated from the delegate should be reused. If set to false, any currently pooled items are destroyed.

See also Reusing items, TableView::pooled, and TableView::reused.


rowHeightProvider : var

This property can hold a function that returns the row height for each row in the model. When assigned, it will be called whenever TableView needs to know the height of a specific row. The function takes one argument, row, for which the TableView needs to know the height.

Note: The height of a row must always be greater than 0.

See also columnWidthProvider and Row heights and column widths.


rowSpacing : real

This property holds the spacing between the rows.

The default value is 0.


rows : int

This property holds the number of rows in the table. This is equal to the number of rows in the model.

This property is read only.


Attached Property Documentation

TableView.view : TableView

This attached property holds the view that manages the delegate instance. It is attached to each instance of the delegate.


Attached Signal Documentation

pooled()

This signal is emitted after an item has been added to the reuse pool. You can use it to pause ongoing timers or animations inside the item, or free up resources that cannot be reused.

This signal is emitted only if the reuseItems property is true.

See also Reusing items, reuseItems, and reused.


reused()

This signal is emitted after an item has been reused. At this point, the item has been taken out of the pool and placed inside the content view, and the model properties such as index, row, and column have been updated.

Other properties that are not provided by the model does not change when an item is reused. You should avoid storing any state inside a delegate, but if you do, manually reset that state on receiving this signal.

This signal is emitted when the item is reused, and not the first time the item is created.

This signal is emitted only if the reuseItems property is true.

See also Reusing items, reuseItems, and pooled.


Method Documentation

forceLayout()

Responding to changes in the model are batched so that they are handled only once per frame. This means the TableView delays showing any changes while a script is being run. The same is also true when changing properties such as rowSpacing or leftMargin.

This method forces the TableView to immediately update the layout so that any recent changes take effect.

Calling this function re-evaluates the size and position of each visible row and column. This is needed if the functions assigned to rowHeightProvider or columnWidthProvider return different values than what is already assigned.


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