diff options
| author | Stephen Kelly <steveire@gmail.com> | 2016-12-18 11:32:27 +0000 |
|---|---|---|
| committer | Stephen Kelly <steveire@gmail.com> | 2016-12-18 21:34:36 +0000 |
| commit | 7adfe7494bb4a2c1d3a036fe9dfd946bc00c5d49 (patch) | |
| tree | 6325897fee2a3b413b9c09e2eff43f75c05d1a90 /src/widgets | |
| parent | 7c402ad3d15ff5e7c2b7319b1bea821f6f67e26c (diff) | |
Update model-view documentation about layoutChanged
This has always been true, but hasn't been documented well enough, so
triagers are giving incorrect information in bug reports (eg QTBUG-47711
and QTBUG-53221). That incorrect information is being treated as truth
by Qt users which take action based on incorrect information. That is a
problem, so try to make the documentation clear.
Change-Id: I4e44a9a0675cdd7d9289ec209ae32d5a92899fc9
Reviewed-by: David Faure <david.faure@kdab.com>
Diffstat (limited to 'src/widgets')
| -rw-r--r-- | src/widgets/doc/src/model-view-programming.qdoc | 19 |
1 files changed, 16 insertions, 3 deletions
diff --git a/src/widgets/doc/src/model-view-programming.qdoc b/src/widgets/doc/src/model-view-programming.qdoc index e727d7fe56..84819e8c1a 100644 --- a/src/widgets/doc/src/model-view-programming.qdoc +++ b/src/widgets/doc/src/model-view-programming.qdoc @@ -2070,9 +2070,22 @@ Normally, the begin and end functions are capable of informing other components about changes to the model's underlying structure. For more complex changes to the - model's structure, perhaps involving internal reorganization or sorting of data, - it is necessary to emit the \l{QAbstractItemModel::layoutChanged()}{layoutChanged()} - signal to cause any attached views to be updated. + model's structure, perhaps involving internal reorganization, sorting of data or + any other structural change, it is necessary to perform the following sequence: + + \li Emit the \l{QAbstractItemModel::layoutAboutToBeChanged()}{layoutAboutToBeChanged()} signal + \li Update internal data which represents the structure of the model. + \li Update persistent indexes using \l{QAbstractItemModel::changePersistentIndexList()}{changePersistentIndexList()} + \li Emit the \l{QAbstractItemModel::layoutChanged()}{layoutChanged()} signal. + + This sequence can be used for any structural update in lieu of the more + high-level and convenient protected methods. For example, if a model of + two million rows needs to have all odd numbered rows removed, that + is 1 million discountiguous ranges of 1 element each. It would be + possible to use beginRemoveRows and endRemoveRows 1 million times, but + that would obviously be inefficient. Instead, this can be signalled as a + single layout change which updates all necessary persistent indexes at + once. \section3 Lazy population of model data |