Handling Selections in Item Views

Updating a Selection

Selection commands are provided by a combination of selection flags, defined by QItemSelectionModel::SelectionFlag. Each selection flag tells the selection model how to update its internal record of selected items when either of the select() functions are called. The most commonly used flag is the Select flag which instructs the selection model to record the specified items as being selected. The Toggle flag causes the selection model to invert the state of the specified items, selecting any deselected items given, and deselecting any currently selected items. The Deselect flag deselects all the specified items.

Individual items in the selection model are updated by creating a selection of items, and applying them to the selection model. In the following code, we apply a second selection of items to the table model shown above, using the Toggle command to invert the selection state of the items given.

     QItemSelection toggleSelection;

     topLeft = model->index(2, 1, QModelIndex());
     bottomRight = model->index(7, 3, QModelIndex());
     toggleSelection.select(topLeft, bottomRight);

     selectionModel->select(toggleSelection, QItemSelectionModel::Toggle);

The results of this operation are displayed in the table view, providing a convenient way of visualizing what we have achieved:

By default, the selection commands only operate on the individual items specified by the model indexes. However, the flag used to describe the selection command can be combined with additional flags to change entire rows and columns. For example if you call select() with only one index, but with a command that is a combination of Select and Rows, the entire row containing the item referred to will be selected. The following code demonstrates the use of the Rows and Columns flags:

     QItemSelection columnSelection;

     topLeft = model->index(0, 1, QModelIndex());
     bottomRight = model->index(0, 2, QModelIndex());

     columnSelection.select(topLeft, bottomRight);

     selectionModel->select(columnSelection,
         QItemSelectionModel::Select | QItemSelectionModel::Columns);

     QItemSelection rowSelection;

     topLeft = model->index(0, 0, QModelIndex());
     bottomRight = model->index(1, 0, QModelIndex());

     rowSelection.select(topLeft, bottomRight);

     selectionModel->select(rowSelection,
         QItemSelectionModel::Select | QItemSelectionModel::Rows);

Although only four indexes are supplied to the selection model, the use of the Columns and Rows selection flags means that two columns and two rows are selected. The following image shows the result of these two selections:

The commands performed on the example model have all involved accumulating a selection of items in the model. It is also possible to clear the selection, or to replace the current selection with a new one.

To replace the current selection with a new selection, combine the other selection flags with the Current flag. A command using this flag instructs the selection model to replace its current collection of model indexes with those specified in a call to select(). To clear all selections before you start adding new ones, combine the other selection flags with the Clear flag. This has the effect of resetting the selection model's collection of model indexes.

     QModelIndex topLeft = model->index(0, 0, parent);
     QModelIndex bottomRight = model->index(model->rowCount(parent)-1,
         model->columnCount(parent)-1, parent);

     QItemSelection selection(topLeft, bottomRight);
     selectionModel->select(selection, QItemSelectionModel::Select);

     QModelIndex parent = QModelIndex();