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c++ - QDbus 信号不工作（暂停交付）

问题描述

对于我的项目，我需要使用带信号的 DBus。为此，我尝试将D-Bus Remote Controlled Car Example中可用的示例程序转换为在 linux ARM A7 处理器（使用 Qt 5.12.8）上运行。我已经意识到以下步骤：

  1. 用文本输出替换所有 HMI 引用并简化程序。
  2. 迁移项目以在 qmake 的地方使用 CMake（最终项目中使用 Cmake > 3.0）

汽车文件夹中的 CMakeLists.txt：

set(QT_LIBS Qt5::Core Qt5::DBus)

add_custom_command(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/car_adaptor.h ${CMAKE_CURRENT_SOURCE_DIR}/car_adaptor.cpp
  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  COMMENT "Generate adaptors files for Dbus service"
  COMMAND /opt/dip/2.7-warrior+snapshot/sysroots/x86_64-dipsdk-linux/usr/bin/qdbusxml2cpp -a car_adaptor.h: ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  COMMAND /opt/dip/2.7-warrior+snapshot/sysroots/x86_64-dipsdk-linux/usr/bin/qdbusxml2cpp -i car_adaptor.h -a :car_adaptor.cpp ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
)

add_executable (car 
  main.cpp 
  car.cpp
  car_adaptor.cpp
)

set_target_properties(car PROPERTIES AUTOMOC TRUE)
target_link_libraries(car ${QT_LIBS})

控制器文件夹中的 CMakeLists.txt：

set(QT_LIBS Qt5::Core Qt5::DBus)

add_custom_command(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/car_interface.h ${CMAKE_CURRENT_SOURCE_DIR}/car_interface.cpp
  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  COMMENT "Generate interface files for Dbus service"
  COMMAND /opt/dip/2.7-warrior+snapshot/sysroots/x86_64-dipsdk-linux/usr/bin/qdbusxml2cpp -p car_interface.h: ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  COMMAND /opt/dip/2.7-warrior+snapshot/sysroots/x86_64-dipsdk-linux/usr/bin/qdbusxml2cpp -i car_interface.h -p :car_interface.cpp ${CMAKE_CURRENT_SOURCE_DIR}/car.xml
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
)

add_executable (controller 
  main.cpp 
  controller.cpp
  car_interface.cpp
) 

set_target_properties(controller PROPERTIES AUTOMOC TRUE)
target_link_libraries(controller ${QT_LIBS})

问题描述

我的问题如下：通过这些更改，Dbus 信号似乎由汽车应用程序发出，但控制器应用程序没有接收到。我试图了解 DBus 调试模式 ( QDBUS_DEBUG=1 ) 问题的根源，但不明白为什么所有信号都有以下返回：QDBusConnectionPrivate(0x75d006d0) 交付被暂停 我可能错过了一件事，但我看不到什么。

测试输出：

export QDBUS_DEBUG=1
eval `dbus-launch --auto-syntax`
root@rzn1-embd:/tmp# ./car &
[1] 1391
root@rzn1-embd:/tmp# QDBusConnectionPrivate(0x75d006d0) : connected successfully
QDBusConnectionPrivate(0x75d006d0) got message (signal): QDBusMessage(type=Signal, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="NameAcquired", signature="s", contents=(":1.0") )
QDBusConnectionPrivate(0x75d006d0) sending message: QDBusMessage(type=MethodCall, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="RequestName", signature="", contents=("org.example.CarExample", 4) )
QDBusConnectionPrivate(0x75d006d0) delivery is suspended
QDBusConnectionPrivate(0x75d006d0) got message (signal): QDBusMessage(type=Signal, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="NameAcquired", signature="s", contents=("org.example.CarExample") )
QDBusConnectionPrivate(0x75d006d0) delivery is suspended
QDBusConnectionPrivate(0x75d006d0) got message reply: QDBusMessage(type=MethodReturn, service="org.freedesktop.DBus", signature="u", contents=(1) )
QDBusConnectionPrivate(0x75d006d0) dequeueing message QDBusMessage(type=Signal, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="NameAcquired", signature="s", contents=(":1.0") )
QDBusConnectionPrivate(0x75d006d0) dequeueing message QDBusMessage(type=Signal, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="NameAcquired", signature="s", contents=("org.example.CarExample") )
root@rzn1-embd:/tmp# ./controller
QDBusConnectionPrivate(0x75d006d0) : connected successfully
QDBusConnectionPrivate(0x75d006d0) got message (signal): QDBusMessage(type=Signal, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="NameAcquired", signature="s", contents=(":1.1") )
QDBusConnectionPrivate(0x75d006d0) delivery is suspended
QDBusConnectionPrivate(0x75d006d0) Adding rule: "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='NameOwnerChanged',arg0='org.example.CarExample'"
QDBusConnectionPrivate(0x75d006d0) sending message: QDBusMessage(type=MethodCall, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="GetNameOwner", signature="", contents=("org.example.CarExample") )
QDBusConnectionPrivate(0x75d006d0) got message reply: QDBusMessage(type=MethodReturn, service="org.freedesktop.DBus", signature="s", contents=(":1.0") )
QDBusConnectionPrivate(0x75d006d0) Adding rule: "type='signal',sender='org.example.CarExample',path='/Car',interface='org.example.Examples.CarInterface',member='crashed'"
QDBusConnectionPrivate(0x75d006d0) sending message: QDBusMessage(type=MethodCall, service="org.freedesktop.DBus", path="/org/freedesktop/DBus", interface="org.freedesktop.DBus", member="GetNameOwner", signature="", contents=("org.example.CarExample") )
QDBusConnectionPrivate(0x75d006d0) got message reply: QDBusMessage(type=MethodReturn, service="org.freedesktop.DBus", signature="s", contents=(":1.0") )
QDBusConnectionPrivate(0x75d006d0) Watching service "org.example.CarExample" for owner changes (current owner: ":1.0" )

Menu:
        - Q: quitter
        - 1: Accelerate
        - 2: Decelerate
1
QDBusConnectionPrivate(0x75d006d0) sending message: QDBusMessage(type=MethodCall, service="org.example.CarExample", path="/Car", interface="org.example.Examples.CarInterface", member="accelerate", signature="", contents=() )
QDBusConnectionPrivate(0x75d006d0) got message (signal): QDBusMessage(type=MethodCall, service=":1.1", path="/Car", interface="org.example.Examples.CarInterface", member="accelerate", signature="", contents=() )
Speed:  1
QDBusConnectionPrivate(0x75d006d0) Automatically sending reply: ()
QDBusConnectionPrivate(0x75d006d0) sending message (no reply): QDBusMessage(type=MethodReturn, service="", signature="", contents=() )
QDBusConnectionPrivate(0x75d006d0) got message reply: QDBusMessage(type=MethodReturn, service=":1.0", signature="", contents=() )
QThread(ptr=0x76f0d370, name=QDBusConnectionManager) emitting signal at "/Car"
QDBusConnectionPrivate(0x75d006d0) got message (signal): QDBusMessage(type=Signal, service=":1.0", path="/Car", interface="org.example.Examples.CarInterface", member="crashed", signature="", contents=() )
QDBusConnectionPrivate(0x75d006d0) delivery is suspended

修改后的源文件：

汽车.h

#ifndef CAR_H
#define CAR_H

#include <QObject>

class Car : public QObject
{
    Q_OBJECT
public:
    Car();

public Q_SLOTS:
    void accelerate();
    void decelerate();

Q_SIGNALS:
    void crashed();

private:
    int speed;       // delta movement along the body axis
};

#endif // CAR_H

汽车.cpp

#include "car.h"
#include <QDebug>

Car::Car() : speed(0) {}

void Car::accelerate() {
  if (speed < 10) 
    ++speed; 
  qInfo() << "Speed: " << speed << endl;
  if (speed > 0) 
    emit crashed(); 
}

void Car::decelerate() {
  if (speed > -10) 
    --speed;
  qInfo() << "Speed: " << speed << endl;
}

汽车/main.cpp

#include "car.h"
#include "car_adaptor.h"
#include <QCoreApplication>
#include <QtDBus/QDBusConnection>

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

  Car *car = new Car();
  new CarInterfaceAdaptor(car);
  QDBusConnection connection = QDBusConnection::sessionBus();
  connection.registerObject("/Car", car);
  connection.registerService("org.example.CarExample");
  return app.exec();
}

控制器/main.cpp

#include <QtDBus>
#include <QCoreApplication>
#include "controller.h"

int main(int argc, char *argv[]) {
  QCoreApplication app(argc, argv);
  Controller       controller;
  controller.start();
  return app.exec();
}

控制器.h

#ifndef CONTROLLER_H
#define CONTROLLER_H

#include "car_interface.h"
#include <QObject>

class Controller : public QObject
{
    Q_OBJECT

public:
    Controller(QObject *parent = 0);
    void start();

private slots:
    void on_accelerate_clicked();
    void on_decelerate_clicked();
    void onCrashed();

private:
    org::example::Examples::CarInterface *car;
    void displayMenu();
};
#endif

控制器.cpp

#include "controller.h"
#include "car_interface.h"
#include <QDebug>

Controller::Controller(QObject *parent) : QObject(parent) {
  car = new org::example::Examples::CarInterface(
      "org.example.CarExample", "/Car", QDBusConnection::sessionBus(), this);
  connect(car, SIGNAL(crashed()), this, SLOT(onCrashed()));
}

void Controller::start() {
  char key = 0;
  displayMenu();
  while (key != 'Q') {
    key = getchar();
    switch (key) {
      case '1': on_accelerate_clicked(); break;
      case '2': on_decelerate_clicked(); break;
      case 'Q': exit(1); break;
    }
  }
}

void Controller::on_accelerate_clicked() { car->accelerate(); }

void Controller::on_decelerate_clicked() { car->decelerate(); }

void Controller::onCrashed() { qInfo() << "Controller: crashed"; }

void Controller::displayMenu() {
  qInfo() << "\r\nMenu:";
  qInfo() << "\t- Q: quitter";
  qInfo() << "\t- 1: Accelerate";
  qInfo() << "\t- 2: Decelerate";
}

标签： c++qtcmakesignalsdbus

解决方案

在控制器的main()函数中，执行永远不会过去controller.start()，因为此方法包含while不断轮询键盘输入的循环，如果按下“Q”，它会立即退出。

因此，您永远无法到达app.exec()运行 Qt 事件循环的位置，并且仅在事件循环内接收和处理 DBus 信号。

您应该切换以处理基于键盘按下事件的事件。或者，如果你想保持while循环，你应该修改它，至少QCoreApplication::processEvents()（参见它的文档）经常被调用。

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