g_signal_connect 代理处理程序导致回调 GVariant * 数据未初始化

Question

为了在 dbus 上设置 Connman 信号回调，我几乎遵循 https://www.freedesktop.org/software/gstreamer-sdk/data/docs/latest/gio/GDBusProxy.html 上的示例，但是在我的回调函数中：

g_signal_connect(
        this->manager_proxy,
        "property-changed",
        G_CALLBACK(on_manager_properties_changed),
        this); //Pass in pointer to self so static function can operate on object.
g_signal_connect(
        this->manager_proxy,
        "technology-added",
        G_CALLBACK(on_manager_tech_added),
        this); //Pass in pointer to self so static function can operate on object.
g_signal_connect(
        this->manager_proxy,
        "technology-removed",
        G_CALLBACK(on_manager_tech_removed),
        this); //Pass in pointer to self so static function can operate on object

void
CM_InterfaceController::on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       GVariant            *changed_properties,
                       const gchar* const  *invalidated_properties,
                       gpointer             user_data)
{
    if(!user_data){CM_ERR("NO THIS * on_manager_properties_changed");return;}
    CM_InterfaceController * ths = static_cast<CM_InterfaceController *>(user_data);
    std::cout<<"on_manager_properties_changed"<<std::endl;
    if(changed_properties){
        std::cout<<"children: "<<g_variant_n_children(changed_properties)<<std::endl;
    }    
}

我被告知 GVariant * object 包含的 children 的数量是完全错误的。比如我的反馈：

Calling Extraction
Service List Size: 1
Identified Ethernet Link: 
Path: /net/connman/service/ethernet_0800277d326e_cable
        Type: ethernet
        Sate: ready
        Favorite: 0
        Auto Connect: 0
        Name: Wired
        Net Mode: manual
        Iface: eth0
        Mac: 08:00:27:7D:32:6E
        IP Address: 10.0.2.15
        Net Mask: 255.255.255.0
on_manager_properties_changed
children: 139764141513856
on_manager_properties_changed
children: 145

on_manager_properties_changed children: 139764141513856 on_manager_properties_changed children: 145

这两个值都超出了范围，一个比另一个更明显。更重要的是，如果我尝试从 GVariant object 中解析值，即使只是尝试调用 g_variant_get_type_string，我也会出现段错误。 为什么我的回调 return 使用垃圾数据指针？ 似乎如果它什么都没有，它至少应该 return 一个空指针。

编辑：Source Code https://drive.google.com/file/d/1E0Kg9JKW54gghUHbVyBJ0ysBIdqBlpVA/view?usp=sharing

还有一些dbus-monitor--系统输出：

signal time=1549641357.679460 sender=:1.3 -> destination=(null destination) serial=488 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "State"
   variant       string "ready"
signal time=1549641357.680844 sender=:1.3 -> destination=(null destination) serial=489 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Nameservers"
   variant       array [
         string "10.0.2.3"
      ]
signal time=1549641357.681186 sender=:1.3 -> destination=(null destination) serial=490 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Domains"
   variant       array [
      ]
signal time=1549641357.681601 sender=:1.3 -> destination=(null destination) serial=491 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "Proxy"
   variant       array [
         dict entry(
            string "Method"
            variant                string "direct"
         )
      ]
signal time=1549641357.681780 sender=:1.3 -> destination=(null destination) serial=492 path=/net/connman/technology/ethernet; interface=net.connman.Technology; member=PropertyChanged
   string "Connected"
   variant       boolean true
signal time=1549641357.682210 sender=:1.3 -> destination=(null destination) serial=493 path=/; interface=net.connman.Manager; member=PropertyChanged
   string "State"
   variant       string "ready"
signal time=1549641357.696004 sender=:1.3 -> destination=(null destination) serial=494 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
      ]
signal time=1549641357.696227 sender=:1.3 -> destination=(null destination) serial=495 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
         dict entry(
            string "Address"
            variant                string "10.0.2.15"
         )
         dict entry(
            string "Netmask"
            variant                string "255.255.255.0"
         )
      ]
signal time=1549641357.696454 sender=:1.3 -> destination=(null destination) serial=496 path=/net/connman/service/ethernet_0800277d326e_cable; interface=net.connman.Service; member=PropertyChanged
   string "IPv4"
   variant       array [
         dict entry(
            string "Method"
            variant                string "dhcp"
         )
         dict entry(
            string "Address"
            variant                string "10.0.2.15"
         )
         dict entry(
            string "Netmask"
            variant                string "255.255.255.0"
         )
         dict entry(
            string "Gateway"
            variant                string "10.0.2.2"
         )
      ]

Answer 1

想通了！

在我的 XML 文件中，我正在观察的信号是：

  <signal name="PropertyChanged">
     <arg name="name" type="s" />
     <arg name="value" type="v" />
  </signal>

尽管我试图弄清楚为什么 freedesktop.org 上的示例回调函数是反向的，但我不得不修改以下内容：

static void on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       GVariant            *changed_properties,
                       const gchar* const  *invalidated_properties,
                       gpointer             user_data);

至：

static void on_manager_properties_changed (
                       GDBusProxy          *proxy,
                       const gchar* const  *invalidated_properties, //(name)
                       GVariant            *changed_properties, //(value)
                       gpointer             user_data);

所以在回调函数中type='s'出现在type='v'之前。在那之后，一切都很好。我想也许无论 freedesktop 的例子正在观察什么信号，都可能是与我想要的不同的信息元素。

g_signal_connect 代理处理程序导致回调 GVariant * 数据未初始化

g_signal_connect on proxy handler results in callback GVariant * data uninitialized

dbus

glib

gdbus

connman