问题描述
我正在实现与嵌入式设备的接口，该接口通过dbus API公开其硬件配置。
目前，我正在研究对设备的硬件I / O引脚的访问。在配置和读取/写入这些引脚时，已经可以按预期方式工作了，但在将这些输入引脚的 PropertiesChanged 信号正确连接到我的qt应用程序的插槽时，我遇到了问题。该信号通知监听者该引脚上当前输入值的变化。
例如，通过dbus-monitor发出信号时，信号如下所示：
signal sender=:1.2 -> dest=(null destination) serial=1023 path=/com/actia/platform/io/freq_in1_std; interface=org.freedesktop.DBus.Properties; member=PropertiesChanged
string "com.actia.platform.io.digital_input"
array [
dict entry(
string "InputValue"
variant int32 17857
)
]
array [
]
代表施加的频率1.7857 kHz的值。
我这样连接到信号：
if (QDBusConnection::sessionBus().connect("com.actia.platform.io","/com/actia/platform/io/freq_in1_std","org.freedesktop.DBus.Properties","PropertiesChanged",this,SLOT(propertyChanged(QString,QVariantMap,QStringList)))) {
qDebug() << "PropertiesChanged signal connected successfully to slot";
} else {
qDebug() << "PropertiesChanged signal connection was not successful";
}
，连接的插槽如下：
void MyClass::propertyChanged(QString name,QVariantMap map,QStringList list)
{
qDebug() << QString("properties of interface %1 changed").arg(name);
for (QVariantMap::const_iterator it = map.cbegin(),end = map.cend(); it != end; ++it) {
qDebug() << "property: " << it.key() << " value: " << it.value();
}
for (const auto& element : list) {
qDebug() << "list element: " << element;
}
}
我看到连接成功完成，但是我认为签名似乎不正确。因为我从来没有看到那个插槽被调用。
这是调试输出的摘录，其中包含一个小示例应用程序类的QDBUS_DEBUG=1，在该实例中，我实例化了一个输入和一个输出引脚，在其中我连接了 PropertiesChanged 信号，然后访问了一些手动设置dbus方法和属性，然后使其空转以等待信号捕获。我评论了一下调试日志。一段时间后，当dbus上的信号被触发多次后，我退出了该应用程序。
### application.debug: start of initialization before issuing QCoreApplication::exec()...
### application.debug: creating a digital out pin...
// comment on the logs: The folloiwing 6 lines of debug output originate of instanciating the matching dbus proxy that has been generated by qdbusxml2cpp
QDBusConnectionPrivate(0x747021d0) : connected successfully
QDBusConnectionPrivate(0x747021d0) got message (signal): QDBusMessage(type=Signal,service="org.freedesktop.DBus",path="/org/freedesktop/DBus",interface="org.freedesktop.DBus",member="NameAcquired",signature="s",contents=(":1.1464") )
QDBusConnectionPrivate(0x747021d0) delivery is suspended
QDBusConnectionPrivate(0x747021d0) Adding rule: "type='signal',sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',member='NameOwnerChanged',arg0='com.actia.platform.io'"
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,member="GetNameOwner",signature="",contents=("com.actia.platform.io") )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,contents=(":1.2") )
### application.debug: Connecting the PropertiesChanged signal for the created pin...
QDBusConnectionPrivate(0x74710460) : connected successfully
QDBusConnectionPrivate(0x74710460) got message (signal): QDBusMessage(type=Signal,contents=(":1.28") )
QDBusConnectionPrivate(0x74710460) delivery is suspended
QDBusConnectionPrivate(0x74710460) Adding rule: "type='signal',sender='com.actia.platform.io',path='/com/actia/platform/io/dout1',interface='org.freedesktop.DBus.Properties',member='PropertiesChanged'"
QDBusConnectionPrivate(0x74710460) sending message: QDBusMessage(type=MethodCall,contents=("com.actia.platform.io") )
QDBusConnectionPrivate(0x74710460) got message reply: QDBusMessage(type=Error,error name="org.freedesktop.DBus.Error.NameHasNoOwner",error message="Could not get owner of name 'com.actia.platform.io': no such name",contents=("Could not get owner of name 'com.actia.platform.io': no such name") )
QDBusConnectionPrivate(0x74710460) Watching service "com.actia.platform.io" for owner changes (current owner: "" )
### application.debug: PropertiesChanged signal connected successfully to slot
### application.debug: creating a digital in pin...
// comment on the logs: The following 2 lines of debug output originate of instanciating the matching dbus proxy that has been generated by qdbusxml2cpp
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,contents=(":1.2") )
### application.debug: Connecting the PropertiesChanged signal for the created pin...
QDBusConnectionPrivate(0x74710460) Adding rule: "type='signal',path='/com/actia/platform/io/freq_in1_std',member='PropertiesChanged'"
### application.debug: PropertiesChanged signal connected successfully to slot
### application.debug: success setting pin modes for the digital out pin to pwm generation: true
// comment on the logs: setting a value on an output pin Now
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,service="com.actia.platform.io",path="/com/actia/platform/io/dout1",interface="com.actia.platform.io.digital_output",member="SetValue",contents=(200,80) )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,service=":1.2",contents=() )
### application.debug: success setting pwm of 20 Hz at 80% duty cycle: true
// comment on the logs: reading back the properties for the pins to verify
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,interface="org.freedesktop.DBus.Properties",member="Get",contents=("com.actia.platform.io.digital_output","OutputFrequency") )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,signature="v",contents=([Variant(int): 200]) )
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,"OutputRatio") )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,contents=([Variant(int): 80]) )
### application.debug: pwm backread frequency 20,duty cycle 80
// comment on the logs: setting the mode of a digital input pin to read a frequency instead a logical 0 or 1
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,path="/com/actia/platform/io/freq_in1_std",interface="com.actia.platform.io.digital_input",member="SetInputType",contents=(2) )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,contents=() )
### application.debug: setting pin modes of the digital in pin to read a frequency: true
// comment on the logs: reading the currently applied frequency from the pin Now
QDBusConnectionPrivate(0x747021d0) sending message: QDBusMessage(type=MethodCall,contents=("com.actia.platform.io.digital_input","InputValue") )
QDBusConnectionPrivate(0x747021d0) got message reply: QDBusMessage(type=MethodReturn,contents=([Variant(int): 17361]) )
### application.debug: reading the current frequency from digital input: 1736.1 Hz
### application.debug: end of actual code during initialization,Now issuing QCoreApplication::exec()...
QDBusConnectionPrivate(0x747021d0) dequeueing message QDBusMessage(type=Signal,contents=(":1.1464") )
QDBusConnectionPrivate(0x74710460) dequeueing message QDBusMessage(type=Signal,contents=(":1.28") )
[...] program running,waiting for signals
### application.debug: QCoreApplication::quit()
QDBusConnectionPrivate(0x74710460) Removing rule: "type='signal',member='PropertiesChanged'"
QDBusConnectionPrivate(0x74710460) Removing rule: "type='signal',member='PropertiesChanged'"
QDBusConnectionPrivate(0x747021d0) disconnected
QDBusConnectionPrivate(0x74710460) disconnected
我在SO或QT论坛上找到了大量关于连接到 PropertiesChanged 信号的建议，并从那里尝试了一些建议，但无济于事。必须存在一些我不知道的签名不匹配。但是，我偷看了诸如networkmanager-qt之类的dbus应用程序的代码，它们使用了我也在签名中使用的三个参数：QString，QVariantMap，QStringList。 / p>
我现在陷入困境，希望任何人都可以提出其他提示。 预先感谢。
解决方法
嗯，我真的不知道为什么。但是，当我使用全新的源qt构建（与以前的版本相同）再次尝试上述确切代码时，它就可以工作。所以我认为目前已经解决了。