Qt Remote Objects Source
At a high level, you can choose to use a QObject type directly as a source; or you can define the desired API in a .rep template for use with the repc compiler.
If you already have a fully defined QObject, you can use it as a source by passing it to QRemoteObjectHostBase::enableRemoting(). This way, other processes or devices can then create dynamics replicas of the object to interact with.
For more information, see Remote Object Interaction.
Letting repc generate a source header file for your project, using the REPC_SOURCE variable, provides three different options to implement the required API.
Suppose your class name is Foo, you then have the following options:
- FooSimpleSource inheritance
- FooSource inheritance
- FooSourceAPI usage with your own QObject
For more details on how to create a .rep file, see The rep file format.
There is a <Type>SimpleSource class defined in the header, which provides the basic getter/setter methods for each property and implements data members of the correct property type in the header. "<Type>" here represents the class name from the .rep file, so if your class is of type "MyType" in the .rep file, then the generated header file will have a MyTypeSimpleSource class declared. This is a quick way to get started using the API. To use this class, you need to write a class that inherits from it and implement any slots defined, which are marked as pure virtual in the generated header file. You need to add the necessary logic to manage the exposed properties and emit signals, to your class as well.
If you need to hide your implementation details, use the second class declared in the header file, the <Type>Source class. This class' definition does not provide data members, and also makes the getter/setter functions pure virtual. While you may need to write more code, using this class gives you more flexibility in your implementation.
The third class generated in the header is <Type>SourceAPI. This is a templated class, for use specifically by the templated version of QRemoteObjectHostBase::enableRemoting(), which allows you to use any QObject that supports the required API as the source. Use this class to hide or convert properties or signal/slot parameters. If your implementation does not provide the correct API, there will be compile-time warnings.
Note: Replicas and sources both derive from QObject; but their QObject API is never exposed. For instance, while a replica has a destroyed signal, the source's destroyed signal is not propagated. The source and each of its replica are unique QObjects with their own connections and lifetimes. Instead, the API that is exposed is defined by the .rep template used by repc. In the case of raw QObjects, all API elements are defined in the inheritance chain from a specific ancestor. The QObject's parent is always used, unless you define Q_CLASSINFO("RemoteObject Type") in an ancestor. If you use Q_CLASSINFO("RemoteObject Type"), that class's API is the lowest level of API used.
Identifying Sources
Because a host node can share more than one source, each source requires a name. All repc-generated headers include a way for the node to determine the class name: Q_CLASSINFO for replica, simplesource, or source types; or a static name() function for the SourceAPI type. If you pass your own QObject type to QRemoteObjectHostBase::enableRemoting(), the name is determined using the following logic:
- A name can optionally be passed to QRemoteObjectHostBase::enableRemoting(). If provided, that name is used.
- If the object or any of its ancestors has Q_CLASSINFO of type "RemoteObject Type" defined, that type name is used.
- If the QObject's objectName is set, then it is used.
- If none of the above are available, the call to QRemoteObjectHostBase::enableRemoting() fails, returning false.