- Qt 6.8
- Qt WebChannel
- C++ Classes
- QWebChannel
- Qt 6.8.0 Reference Documentation

# QWebChannel Class

Exposes QObjects to remote HTML clients. More...

Header: | `#include <QWebChannel>`
qmake: | `QT += webchannel`
Inherits: | QObject

- List of all members, including inherited members

## Properties

- blockUpdates : bool
- propertyUpdateInterval : int

## Public Functions

| QWebChannel(QObject *parent = nullptr)
virtual | ~QWebChannel()
QBindable<bool> | bindableBlockUpdates()
QBindable<int> | bindablePropertyUpdateInterval()
bool | blockUpdates() const
void | deregisterObject(QObject *object)
int | propertyUpdateInterval() const
void | registerObject(const QString &id, QObject *object)
void | registerObjects(const QHash<QString, QObject *> &objects)
QHash<QString, QObject *> | registeredObjects() const
void | setBlockUpdates(bool block)
void | setPropertyUpdateInterval(int ms)

## Public Slots

void | connectTo(QWebChannelAbstractTransport *transport)
void | disconnectFrom(QWebChannelAbstractTransport *transport)

## Signals

void | blockUpdatesChanged(bool block)

## Detailed Description

The QWebChannel fills the gap between C++ applications and HTML/JavaScript applications. By publishing a QObject derived object to a QWebChannel and using the qwebchannel.js on the HTML side, one can transparently access properties and public slots and methods of the QObject. No manual message passing and serialization of data is required, property updates and signal emission on the C++ side get automatically transmitted to the potentially remotely running HTML clients. On the client side, a JavaScript object will be created for any published C++ QObject. It mirrors the C++ object's API and thus is intuitively useable.

QWebChannel transparently supports QFuture. When a client calls a method that returns a QFuture, QWebChannel will send a response with the QFuture result only after the QFuture has finished.

Custom conversion of types to and from JSON is supported by defining converters with QMetaType::registerConverter() to and from QJsonValue. Note that custom converters from QJsonValue to a concrete type must fail if the QJsonValue does not match the expected format. Otherwise QWebChannel cannot fall back to its default conversion mechanisms. Custom converters are also available on the JavaScript side.

The C++ QWebChannel API makes it possible to talk to any HTML client, which could run on a local or even remote machine. The only limitation is that the HTML client supports the JavaScript features used by `qwebchannel.js`. As such, one can interact with basically any modern HTML browser or standalone JavaScript runtime, such as node.js.

There also exists a declarative WebChannel API.

See also Qt WebChannel Standalone Example, JavaScript API, and QMetaType::registerConverter().

## Property Documentation

### `[bindable]` blockUpdates : bool

Note: This property supports QProperty bindings.

When set to `true`, updates are blocked and remote clients will not be notified about property changes.

The changes are recorded and sent to the clients once updates become unblocked again by setting this property to `false`. By default, updates are not blocked.

### `[bindable]` propertyUpdateInterval : int

Note: This property supports QProperty bindings.

This property holds the property update interval.

This interval can be changed to a different interval in milliseconds by setting it to a positive value. Property updates are batched and sent out after the interval expires. If set to zero, the updates occurring within a single event loop run are batched and sent out on the next run. If negative, updates will be sent immediately. Default value is 50 milliseconds.

## Member Function Documentation

### `[explicit]` QWebChannel::QWebChannel(QObject *parent = nullptr)

Constructs the QWebChannel object with the given parent.

Note that a QWebChannel is only fully operational once you connect it to a QWebChannelAbstractTransport. The HTML clients also need to be setup appropriately using `qwebchannel.js`.

### `[virtual noexcept]` QWebChannel::~QWebChannel()

Destroys the QWebChannel.

### `[slot]` void QWebChannel::connectTo(QWebChannelAbstractTransport *transport)

Connects the QWebChannel to the given transport object.

The transport object then handles the communication between the C++ application and a remote HTML client.

See also QWebChannelAbstractTransport and QWebChannel::disconnectFrom().

### `[invokable]` void QWebChannel::deregisterObject(QObject *object)

Deregisters the given object from the QWebChannel.

Remote clients will receive a `destroyed` signal for the given object.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also QWebChannel::registerObjects(), QWebChannel::registerObject(), and QWebChannel::registeredObjects().

### `[slot]` void QWebChannel::disconnectFrom(QWebChannelAbstractTransport *transport)

Disconnects the QWebChannel from the transport object.

See also QWebChannel::connectTo().

### `[invokable]` void QWebChannel::registerObject(const QString &id, QObject *object)

Registers a single object to the QWebChannel.

The properties, signals and public methods of the object are published to the remote clients. There, an object with the identifier id is then constructed.

A property that is `BINDABLE` but does not have a `NOTIFY` signal will have working property updates on the client side, but no mechanism to register a callback for the change notifications.

Note: A current limitation is that objects must be registered before any client is initialized.

Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.

See also QWebChannel::registerObjects(), QWebChannel::deregisterObject(), and QWebChannel::registeredObjects().

### void QWebChannel::registerObjects(const QHash<QString, QObject *> &objects)

Registers a group of objects to the QWebChannel.

The properties, signals and public invokable methods of the objects are published to the remote clients. There, an object with the identifier used as key in the objects map is then constructed.

Note: A current limitation is that objects must be registered before any client is initialized.

See also QWebChannel::registerObject(), QWebChannel::deregisterObject(), and QWebChannel::registeredObjects().

### QHash<QString, QObject *> QWebChannel::registeredObjects() const

Returns the map of registered objects that are published to remote clients.

See also QWebChannel::registerObjects(), QWebChannel::registerObject(), and QWebChannel::deregisterObject().