Call Slot In Qt
Slots in D-Bus adaptors are declared just like normal, public slots, but their parameters must follow certain rules (see The Qt D-Bus Type System for more information). Slots whose parameters do not follow those rules or that are not public will not be accessible via D-Bus.
Slots can have one parameter of type const QDBusMessage &, which must appear at the end of the input parameter list, before any output parameters. This parameter, if present, will be initialized with a copy of the current message being processed, which allows the callee to obtain information about the caller, such as its connection name.
Hi friends, I'm trying to figure out how to call a function from a Slot. The reason I want this as a function is it is something that will be called from multiple different slots. Here is an example of what I'm trying to make work: from PySide2.QtWidgets.
Slots can be of three kinds:
Let’s hit the green run button in Qt Creator to see how it works. The debug output shows the initial method call from main.cpp and with a click on the button another message appears: MyGlobalObject doSomething called with “TEXT FROM QML” That’s all we need to call methods of a C Object from QML. A slot is a function that is called in response to a particular signal. Qt's widgets have many pre-defined slots, but it is common practice to subclass widgets and add your own slots so that you can handle the signals that you are interested in. The QTimer::singleShot is used to call a slot/lambda asynchronously after n ms. The basic syntax is: QTimer::singleShot(myTime, myObject, SLOT(myMethodInMyObject)); with myTime the time in ms, myObject the object which contain the method and myMethodInMyObject the slot to call. So for example if you want to have a timer who write a debug.
- Asynchronous
- Input-only
- Input-and-output
Asynchronous Slots
Asynchronous slots are those that do not normally return any reply to the caller. For that reason, they cannot take any output parameters. In most cases, by the time the first line of the slot is run, the caller function has already resumed working.
However, slots must not rely on that behavior. Scheduling and message-dispatching issues could change the order in which the slot is run. Code intending to synchronize with the caller should provide its own method of synchronization.
Asynchronous slots are marked by the keyword Q_NOREPLY in the method signature, before the void return type and the slot name. The quit() slot in the D-Bus Complex Ping Pong Example is an example of this.
Input-Only Slots
Input-only slots are normal slots that take parameters passed by value or by constant reference. However, unlike asynchronous slots, the caller is usually waiting for completion of the callee before resuming operation. Therefore, non-asynchronous slots should not block or should state it its documentation that they may do so.
Input-only slots have no special marking in their signature, except that they take only parameters passed by value or by constant reference. Optionally, slots can take a QDBusMessage parameter as a last parameter, which can be used to perform additional analysis of the method call message.
Input and Output Slots
Like input-only slots, input-and-output slots are those that the caller is waiting for a reply. Unlike input-only ones, though, this reply will contain data. Slots that output data may contain non-constant references and may return a value as well. However, the output parameters must all appear at the end of the argument list and may not have input arguments interleaved. Optionally, a QDBusMessage argument may appear between the input and the output arguments.
Automatic Replies
Method replies are generated automatically with the contents of the output parameters (if there were any) by the Qt D-Bus implementation. Slots need not worry about constructing proper QDBusMessage objects and sending them over the connection.
However, the possibility of doing so remains there. Should the slot find out it needs to send a special reply or even an error, it can do so by using QDBusMessage::createReply() or QDBusMessage::createErrorReply() on the QDBusMessage parameter and send it with QDBusConnection::send(). The Qt D-Bus implementation will not generate any reply if the slot did so.
Warning: When a caller places a method call and waits for a reply, it will only wait for a limited amount of time. Slots intending to take a long time to complete should make that fact clear in documentation so that callers properly set higher timeouts.
Delayed Replies
Call Slot In Qtc
In some circumstances, the called slot may not be able to process the request immediately. This is frequently the case when the request involves an I/O or networking operation which may block.
If this is the case, the slot should return control to the application's main loop to avoid freezing the user interface, and resume the process later. To accomplish this, it should make use of the extra QDBusMessage parameter at the end of the input parameter list and request a delayed reply.
We do this by writing a slot that stores the request data in a persistent structure, indicating to the caller using QDBusMessage::setDelayedReply(true) that the response will be sent later.
Qt Call Slot In Different Thread
In this case, the return value is unimportant; we return an arbitrary value to satisfy the compiler.
When the request is processed and a reply is available, it should be sent using the QDBusMessage object that was obtained. In our example, the reply code could be something as follows:
As can be seen in the example, when a delayed reply is in place, the return value(s) from the slot will be ignored by Qt D-Bus. They are used only to determine the slot's signature when communicating the adaptor's description to remote applications, or in case the code in the slot decides not to use a delayed reply.
The delayed reply itself is requested from Qt D-Bus by calling QDBusMessage::reply() on the original message. It then becomes the resposibility of the called code to eventually send a reply to the caller.
Call Slot In Qt Code
Warning: When a caller places a method call and waits for a reply, it will only wait for a limited amount of time. Slots intending to take a long time to complete should make that fact clear in documentation so that callers properly set higher timeouts.
See also Using Qt D-Bus Adaptors, Declaring Signals in D-Bus Adaptors, The Qt D-Bus Type System, QDBusConnection, and QDBusMessage.
Call Slot In Qt Download
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