[vlc-devel] [PATCH 3/3] qt: allow getCount to initiate the cache in MLBaseModel

[Pierre Lamot]

On 2020-12-17 13:40, Romain Vimont wrote:
> On Thu, Dec 17, 2020 at 01:32:50PM +0100, Pierre Lamot wrote:
>>   The count property might be accessed before browsing the model.
> 
> But if that's the case, m_cache should be nullptr, and the current
> implementation should work, doesn't it?

this is rather about initializing the cache. My use case was something 
like:

MyModel {
   id: model
   ml: medialib
}

Loader {
   active: model.count > 0
   sourceComponent: WidgetUsingMyModel {
       // ommited [...]
   }
}


In this case, the count property would stay to 0 as the model is never 
browsed, hence the chache is never created

>> ---
>>  modules/gui/qt/medialibrary/mlbasemodel.cpp | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff --git a/modules/gui/qt/medialibrary/mlbasemodel.cpp 
>> b/modules/gui/qt/medialibrary/mlbasemodel.cpp
>> index 4549dacb57..68eb28dac9 100644
>> --- a/modules/gui/qt/medialibrary/mlbasemodel.cpp
>> +++ b/modules/gui/qt/medialibrary/mlbasemodel.cpp
>> @@ -237,7 +237,7 @@ void MLBaseModel::unsetSortCriteria()
>> 
>>  int MLBaseModel::rowCount(const QModelIndex &parent) const
>>  {
>> -    if (parent.isValid())
>> +    if (!m_mediaLib || parent.isValid())
>>          return 0;
> 
> Is rowCount() called while medialib is not set yet?
> I'm surprised, because the medialib is passed as a QML property, it
> should be called before any rowCount() I guess.

I don't think there is practical use for this but you can call rowCount 
manually from QML (in your onComplete for instance, where the m_medialib 
may not be set yet)
in practice, we would rather use the count property

> 
>> 
>>      validateCache();
>> @@ -302,7 +302,10 @@ QVariantList 
>> MLBaseModel::getIdsForIndexes(QVariantList indexes) const
>> 
>>  unsigned MLBaseModel::getCount() const
>>  {
>> -    if (!m_cache || m_cache->count() == COUNT_UNINITIALIZED)
>> +    if (!m_mediaLib)
>> +        return 0;
>> +    validateCache();
>> +    if (m_cache->count() == COUNT_UNINITIALIZED)
>>          return 0;
>>      return static_cast<unsigned>(m_cache->count());
>>  }
>> --
>> 2.25.1
>> 
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