passing QMultiMap to Q_ARG?

[hunsrus]

Hi everybody,

I'm trying to pass the following Map to Qts Meta-System to the method QMetaObject::invokeMethod:

QMultiMap<QString, int>

QMultiMap<QString, int>

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using

QMetaObject::invokeMethod(object,
                      "method",
                      Qt::BlockingQueuedConnection,
                      Q_ARG(QMultiMap<QString, int>, m_map));

QMetaObject::invokeMethod(object,
                      "method",
                      Qt::BlockingQueuedConnection,
                      Q_ARG(QMultiMap<QString, int>, m_map));

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where m_map is defined as:

QMultiMap<QString, int> m_map;

QMultiMap<QString, int> m_map;

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Using the statement above I get:
macro "Q_ARG" passed 3 arguments, but takes just 2

Surrounding the QMultiMap as follows:

Q_ARG((QMultiMap<QString, int>), m_map));

Q_ARG((QMultiMap<QString, int>), m_map));

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results in:
template argument 1 is invalid

Does anyone know how to pass Generic containers as QMap or QMultiMap to invokeMethod?

Thanks in advance,
Jan

[amleto]

try a typedef

typedef QMultiMap<QString, int> QMMap;
...
QMetaObject::invokeMethod(object,
                      "method",
                      Qt::BlockingQueuedConnection,
                      Q_ARG(QMMap, m_map));

typedef QMultiMap<QString, int> QMMap;
...
QMetaObject::invokeMethod(object,
                      "method",
                      Qt::BlockingQueuedConnection,
                      Q_ARG(QMMap, m_map));

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[hunsrus]

Thanks for your reply!
I did it the way you explained now. Just to know: is there another possibility to do this?

[amleto]

I doubt it. Commas tend to break macros and since your attempt to fix it by using extra brackets didn't work (that's also the only inline solution that I know), the only other thing I could think of is typedef.

[tarry1583]

HI ,
Facing an issue for passing a pointer as QARG in invokeMethod :

I am calling the api void CAppManager::launchUrl(const int f_iXcoord,const int f_iYcoord,const int f_iHeight, const int f_iWidth,const QString f_cobjUrl,unsigned long *f_ulRenHandle,bool bSetupURL) as

QMetaObject::invokeMethod(this,"launchUrl",Qt::Que uedConnection,
Q_ARG(int,0),Q_ARG(int,0),Q_ARG(int,480),Q_ARG(int ,800),Q_ARG(QString,sSetUpURL),Q_ARG(unsigned long*,handle),Q_ARG(bool,true));

The issue seems to be with ARG f_ulRenHandle . As when the function had this argument only as pass by value and in InvokeMethod I had passed just Q_ARG(unsigned long,handle) instead of Q_ARG(unsigned long*,handle).It worked.
handle here has to be pointer or refrence as its getting modified in launchURL API .Here I am using pointer as we can't use Refrences with Q_ARG.Here invoke method is always returning 0.
I am initializing/declaring handle as follows :
unsigned long dummyHandle=0;
unsigned long * handle = &dummyHandle;
Please let me know what measure should i take to solve this issue ?

[amleto]

maybe you need to register 'unsigned int*' as a meta type?

[tarry1583]

NO i had tried with registering this datatype as well (unsigned long * ). But the code didn't work .
In Qt help , i had read " Q_ARG() takes a type name and a const reference of that type; Q_RETURN_ARG() takes a type name and a non-const reference." .Does this mean that the datatype has to be always constant with Q_ARG for invokeMethod , and we can never use a pointer and refrence for a variable passes as ARG which can be modified inside the api called like launchURL Api is modifying handle in the case i had mentioned .

[amleto]

If you just wish to change the int value, then you are not changing the pointer value... Passing a pointer for a method to change the pointed thing should be fine according to the doc quotes you have stated.

You do have an alternative, though:
"handle here has to be pointer or refrence as its getting modified in launchURL API .Here I am using pointer as we can't use Refrences with Q_ARG"
If you can change the launchURL API then you can use Q_RETURN_ARG and pass in an unsigned long - it will take it as a reference.