Qt-interest Archive, August 2006
avoiding signal loops
Message 1 in thread
What practices does everyone have for the classic problem of blocking
infinite signal loops created in situations like the following:
** keep two lists in sync **
QListWidget1 => itemSelectionChanged => QListWidget2 =>
itemSelectionChanged => QListWidget1 => itemSelectionChanged => etc...
I've used a noemit bool and just put the following at the beginning
and end of each slot:
if(noemit)
return;
noemit = true;
...
noemit = false;
Does anyone have a cleaner solution? thanks
--
[ signature omitted ]
Message 2 in thread
> I've used a noemit bool and just put the following at the beginning
> and end of each slot:
>
> if(noemit)
> return;
> noemit = true;
> ...
> noemit = false;
>
> Does anyone have a cleaner solution? thanks
Only emit when your state actually changes. Such that in your slot you
should have:
public slots:
void setSomething(int something)
{
if( m_something = something )
{
// No point doing anything....
return;
}
m_something = something;
emit somethingChanged(m_something);
}
begin:vcard
begin:vcard
fn:Justin Noel
n:Noel;Justin
org:(ICS) Integrated Computer Solutions ;Engineering
adr:;;54B Middlesex Turnpike;Bedford;MA;01730;USA
email;internet:justin@xxxxxxx
title:Senior Consulting Engineer / Certified Qt Instructor
tel;work:(617) 621-0060
x-mozilla-html:FALSE
url:http://www.ics.com
version:2.1
end:vcard
Message 3 in thread
Oops guys that ought to be:
public slots:
void setSomething(int something)
{
if( m_something == something )
{
// No point doing anything....
return;
}
m_something = something;
emit somethingChanged(m_something);
}
//Must get more coffee...
Justin Noel wrote:
>
>> I've used a noemit bool and just put the following at the beginning
>> and end of each slot:
>>
>> if(noemit)
>> return;
>> noemit = true;
>> ...
>> noemit = false;
>>
>> Does anyone have a cleaner solution? thanks
> Only emit when your state actually changes. Such that in your slot you
> should have:
>
> public slots:
> void setSomething(int something)
> {
> if( m_something == something )
> {
> // No point doing anything....
> return;
> }
>
> m_something = something;
> emit somethingChanged(m_something);
> }
>
>
begin:vcard
begin:vcard
fn:Justin Noel
n:Noel;Justin
org:(ICS) Integrated Computer Solutions ;Engineering
adr:;;54B Middlesex Turnpike;Bedford;MA;01730;USA
email;internet:justin@xxxxxxx
title:Senior Consulting Engineer / Certified Qt Instructor
tel;work:(617) 621-0060
x-mozilla-html:FALSE
url:http://www.ics.com
version:2.1
end:vcard
Message 4 in thread
>>> I've used a noemit bool and just put the following at the beginning
>>> and end of each slot:
>>>
>>> if(noemit)
>>> return;
>>> noemit = true;
>>> ...
>>> noemit = false;
>>>
>>> Does anyone have a cleaner solution? thanks
What about calling QObject::blockSignals(bool) on the object you are about to change? The logic is similar, but it is built into the Qt library.
-Andrew Vick
--
[ signature omitted ]
