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Diffstat (limited to 'src/widgets/doc')
-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 |