The QModelRoleDataSpan class provides a span over QModelRoleData objects. More...
#include <qabstractitemmodel.h>
Public Member Functions | |
| constexpr | QModelRoleDataSpan () noexcept |
| constexpr | QModelRoleDataSpan (QModelRoleData &modelRoleData) noexcept |
| constexpr | QModelRoleDataSpan (QModelRoleData *modelRoleData, qsizetype len) |
| template<typename Container , if_compatible_container< Container > = true> | |
| constexpr | QModelRoleDataSpan (Container &c) noexcept(noexcept(std::data(c)) &&noexcept(std::size(c))) |
| constexpr qsizetype | size () const noexcept |
| constexpr qsizetype | length () const noexcept |
| constexpr QModelRoleData * | data () const noexcept |
| constexpr QModelRoleData * | begin () const noexcept |
| constexpr QModelRoleData * | end () const noexcept |
| constexpr QModelRoleData & | operator[] (qsizetype index) const |
| constexpr QVariant * | dataForRole (int role) const |
Detailed Description
The QModelRoleDataSpan class provides a span over QModelRoleData objects.
\inmodule QtCore
- Since
- 6.0
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:
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.
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:
- See also
- {Model/View Programming}, QAbstractItemModel::multiData()
Definition at line 101 of file qabstractitemmodel.h.
Constructor & Destructor Documentation
◆ QModelRoleDataSpan() [1/4]
|
inlineconstexprnoexcept |
Constructs an empty QModelRoleDataSpan. Its data() will be set to \nullptr, and its length to zero.
Definition at line 110 of file qabstractitemmodel.h.
◆ QModelRoleDataSpan() [2/4]
|
inlineconstexprnoexcept |
Constructs an QModelRoleDataSpan spanning over modelRoleData, seen as a 1-element array.
Definition at line 112 of file qabstractitemmodel.h.
◆ QModelRoleDataSpan() [3/4]
|
inlineconstexpr |
Constructs an QModelRoleDataSpan spanning over the array beginning at modelRoleData and with length len.
- Note
- The array must be kept alive as long as this object has not been destructed.
Definition at line 117 of file qabstractitemmodel.h.
◆ QModelRoleDataSpan() [4/4]
|
inlineconstexprnoexcept |
Constructs an QModelRoleDataSpan spanning over the container c, which can be any contiguous container of QModelRoleData objects. For instance, it can be a {QVector<QModelRoleData>}, a {std::array<QModelRoleData, 10>} and so on.
- Note
- The container must be kept alive as long as this object has not been destructed.
Definition at line 123 of file qabstractitemmodel.h.
Member Function Documentation
◆ begin()
|
inlineconstexprnoexcept |
Returns a pointer to the beginning of the span represented by this object.
Definition at line 131 of file qabstractitemmodel.h.
◆ data()
|
inlineconstexprnoexcept |
Returns a pointer to the beginning of the span represented by this object.
Definition at line 130 of file qabstractitemmodel.h.
◆ dataForRole()
Returns the data associated with the first QModelRoleData in the span that has its role equal to role. If such a QModelRoleData object does not exist, the behavior is undefined.
- Note
- Avoid calling this function from the model's side, as a model cannot possibly know in advance which roles are in a given QModelRoleDataSpan. This function is instead suitable for views and delegates, which have control over the roles in the span.
- See also
- QModelRoleData::data()
Definition at line 135 of file qabstractitemmodel.h.
◆ end()
|
inlineconstexprnoexcept |
Returns a pointer to the imaginary element one past the end of the span represented by this object.
Definition at line 132 of file qabstractitemmodel.h.
◆ length()
|
inlineconstexprnoexcept |
Returns the length of the span represented by this object.
Definition at line 129 of file qabstractitemmodel.h.
◆ operator[]()
|
inlineconstexpr |
Returns a modifiable reference to the QModelRoleData at position index in the span.
- Note
- index must be a valid index for this span (0 <= index < size()).
Definition at line 133 of file qabstractitemmodel.h.
◆ size()
|
inlineconstexprnoexcept |
Returns the length of the span represented by this object.
Definition at line 128 of file qabstractitemmodel.h.
The documentation for this class was generated from the following files:
- src/corelib/itemmodels/qabstractitemmodel.h
- src/corelib/itemmodels/qabstractitemmodel.cpp
