PySide6.QtCore.QModelRoleDataSpan¶

class QModelRoleDataSpan¶

The QModelRoleDataSpan class provides a span over QModelRoleData objects. More…

Synopsis¶

Methods¶

def __init__()
def __getitem__()
def __len__()
def begin()
def data()
def end()
def length()
def operator[]()
def size()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description¶

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

A QModelRoleDataSpan is used as an abstraction over an array of QModelRoleData objects.

Like a view, QModelRoleDataSpan provides a small object (pointer and size) that can be passed to functions that need to examine the contents of the array. A QModelRoleDataSpan can be constructed from any array-like sequence (plain arrays, QVector , std::vector, QVarLengthArray , and so on). Moreover, it does not own the sequence, which must therefore be kept alive longer than any QModelRoleDataSpan objects referencing it.

Unlike a view, QModelRoleDataSpan is a span, so it allows for modifications to the underlying elements.

QModelRoleDataSpan ‘s main use case is making it possible for a model to return the data corresponding to different roles in one call.

In order to draw one element from a model, a view (through its delegates) will generally request multiple roles for the same index by calling data() as many times as needed:

text = model.data(index, Qt.ItemDataRole.DisplayRole)
decoration = model.data(index, Qt.DecorationRole)
checkState = model.data(index, Qt.CheckStateRole)
# etc.

QModelRoleDataSpan allows a view to request the same data using just one function call.

This is achieved by having the view prepare a suitable array of QModelRoleData objects, each initialized with the role that should be fetched. The array is then wrapped in a QModelRoleDataSpan object, which is then passed to a model’s multiData() function.

std.array<QModelRoleData, 3> roleData = { {
    QModelRoleData(Qt.ItemDataRole.DisplayRole),
    QModelRoleData(Qt.DecorationRole),
    QModelRoleData(Qt.CheckStateRole)
} }
# Usually, this is not necessary: A QModelRoleDataSpan
# will be built automatically for you when passing an array-like
# container to multiData().
span = QModelRoleDataSpan(roleData)
model.multiData(index, span)
# Use roleData[0].data(), roleData[1].data(), etc.

Views are encouraged to store the array of QModelRoleData objects (and, possibly, the corresponding span) and re-use it in subsequent calls to the model. This allows to reduce the memory allocations related with creating and returning QVariant objects.

Finally, given a QModelRoleDataSpan object, the model’s responsibility is to fill in the data corresponding to each role in the span. How this is done depends on the concrete model class. Here’s a sketch of a possible implementation that iterates over the span and uses setData() on each element:

def multiData(self, index, roleDataSpan):

    for roleData in roleDataSpan:
        role = roleData.role()
        # ... obtain the data for index and role ...
        roleData.setData(result)