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Posts tagged with 'cpp'

mandel

dbus-cpp is the libary that we are currently using to perform dbus calls from cpp within ubuntu touch. For those that are used to dbus-cpp know that the dbus interface can be defined via structures that are later checked at compile time. The following is an example of those definitions:

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struct Geoclue
{
    struct Master
    {
        struct Create
        {
            inline static std::string name()
            {
                return "Create";
            } typedef Master Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
    };
 
    struct MasterClient
    {
        struct SetRequirements
        {
            inline static std::string name()
            {
                return "SetRequirements";
            } typedef MasterClient Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
        struct GetAddressProvider
        {
            inline static std::string name()
            {
                return "GetAddressProvider";
            } typedef MasterClient Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
        struct GetPositionProvider
        {
            inline static std::string name()
            {
                return "GetPositionProvider";
            } typedef MasterClient Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
    };
 
    struct Address
    {
        struct GetAddress
        {
            inline static std::string name()
            {
                return "GetAddress";
            } typedef Address Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
    };
 
    struct Position
    {
        struct GetPosition
        {
            inline static std::string name()
            {
                return "GetPosition";
            } typedef Position Interface;
            inline static const std::chrono::milliseconds default_timeout() { return std::chrono::seconds{1}; }
        };
        struct Signals
        {
            struct PositionChanged
            {
                inline static std::string name()
                {
                    return "PositionChanged";
                };
                typedef Position Interface;
                typedef std::tuple<int32_t, int32_t, double, double, double, dbus::types::Struct<std::tuple<int32_t, double, double>>> ArgumentType;
            };
        };
    };
};
}

This is quite a lot of work and quite repetitive. We did notice that and used in some of our projects a set of macros to make us type less. We now will provide the following macros for other developers to use as part of dbus-cpp

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/*
 * Copyright © 2014 Canonical Ltd.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License version 3,
 * as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of+
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 * Authored by: Thomas Voß <thomas.voss@canonical.com>
 */
 
#ifndef CORE_DBUS_MACROS_H_
#define CORE_DBUS_MACROS_H_
 
#include <core/dbus/types/object_path.h>
 
#include <chrono>
#include <string>
 
#define DBUS_CPP_METHOD_WITH_TIMEOUT_DEF(Name, Itf, Timeout) \
 struct Name \
 { \
 typedef Itf Interface; \
 inline static const std::string& name() \
 { \
 static const std::string s{#Name}; \
 return s; \
 } \
 inline static const std::chrono::milliseconds default_timeout() { return std::chrono::milliseconds{Timeout}; } \
 };\

#define DBUS_CPP_METHOD_DEF(Name, Itf) DBUS_CPP_METHOD_WITH_TIMEOUT_DEF(Name, Itf, 2000)
 
#define DBUS_CPP_SIGNAL_DEF(Name, Itf, ArgType) \
 struct Name \
 { \
 inline static std::string name() \
 { \
 return #Name; \
 }; \
 typedef Itf Interface; \
 typedef ArgType ArgumentType; \
 };\

#define DBUS_CPP_READABLE_PROPERTY_DEF(Name, Itf, Type) \
 struct Name \
 { \
 inline static std::string name() \
 { \
 return #Name; \
 }; \
 typedef Itf Interface; \
 typedef Type ValueType; \
 static const bool readable = true; \
 static const bool writable = false; \
 }; \

#define DBUS_CPP_WRITABLE_PROPERTY_DEF(Name, Itf, Type) \
 struct Name \
 { \
 inline static std::string name() \
 { \
 return #Name; \
 }; \
 typedef Itf Interface; \
 typedef Type ValueType; \
 static const bool readable = true; \
 static const bool writable = true; \
 }; \

#endif // CORE_DBUS_MACROS_H_

Using those macros the above example is as follows

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struct Geoclue
{
    struct Master
    {
        DBUS_CPP_METHOD_DEF(Create, Master);
    };
 
    struct MasterClient
    {
        DBUS_CPP_METHOD_DEF(SetRequirements, MasterClient);
        DBUS_CPP_METHOD_DEF(GetAddressProvider, MasterClient);
        DBUS_CPP_METHOD_DEF(GetPositionProvider, MasterClient);
    };
 
    struct Address
    {
        DBUS_CPP_METHOD_DEF(GetAddress, Address);
    };
 
    struct Position
    {
        DBUS_CPP_METHOD_DEF(GetPosition, Position);
        struct Signals
        {
            DBUS_CPP_SIGNAL_DEF(PositionChanged, Position);
        };
    };
};
}

As you can see the amount of code that needs to be written is a lot less and a new developer can easily understand what is going on. Happy coding ;)

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mandel

Ok, imaging that you are working with Qt 5 and using the new way to connect signals, lets for example say we are working with QNetworkReply and we want to have a slot for the QNetworkReply::error signals that takes a QNetworkReply::NetworkError, the way to do it is the following:

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connect(_reply, static_cast<void(QNetworkReply::*)
    (QNetworkReply::NetworkError)>(&QNetworkReply::error),
        this, &MyClass::onNetworkError)

The static_cast is helping the compiler know what method (the signals or the actual method) you are talking about. I know, it is not nice at all but works at compile time better than getting a qWarning at runtime.

The problem is that without the help the compiler does not know what method error you are talking about :-/

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mandel

I have recently been doing some work with Qt and DBus and I got stuck a little on how to correctly send a {sv} over DBus. Either my google-fu is terrible or there are not many examples on how to do this, therefore here is a small static method that will return a {sv} that can be send via DBus without getting a wrong parameters error:

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#ifndef DBUS_HELPER_H
#define DBUS_HELPER_H
 
#include 
#include 
#include 
#include 
 
typedef QHash DBusStringHash;
class DBusHelper : public QObject
{
    Q_OBJECT
public:
    static int DBUS_STRING_MAP_ID;
 
    explicit DBusHelper(QObject *parent = 0);
 
    static class _init
    {
        public:
            _init()
            {
                // diff actions to init
                qRegisterMetaType("DBusStringHash");
                qDBusRegisterMetaType();
                DBUS_STRING_MAP_ID = QMetaType::type("DBusStringHash");
            }
    } _initializer;
 
    static QVariant getVariant(DBusStringHash hash);
 
};
 
Q_DECLARE_METATYPE(DBusStringHash)
#endif // DBUS_HELPER_H
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// required for the init
int DBusHelper::DBUS_STRING_MAP_ID = 0;
DBusHelper::_init DBusHelper::_initializer;
 
DBusHelper::DBusHelper(QObject *parent) :
    QObject(parent)
{
}
 
QVariant DBusHelper::getVariant(DBusStringHash hash)
{
    return QVariant(DBUS_STRING_MAP_ID, &amp;hash);
}

I added the init trick so that there is no need to manually register the types. I hope it helps!

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