The QModelRoleDataSpan class provides a span over QModelRoleData 对象。 更多...
| 头： | #include <QModelRoleDataSpan> |
| CMake: |
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
| qmake: | QT += core |
| Since: | Qt 6.0 |
| QModelRoleDataSpan () | |
| QModelRoleDataSpan (QModelRoleData & modelRoleData ) | |
| QModelRoleDataSpan (QModelRoleData * modelRoleData , qsizetype len ) | |
| QModelRoleDataSpan (Container & c ) | |
| QModelRoleData * | begin () const |
| QModelRoleData * | data () const |
| QVariant * | dataForRole (int role ) const |
| QModelRoleData * | end () const |
| qsizetype | length () const |
| qsizetype | size () const |
| QModelRoleData & | operator[] (qsizetype index ) const |
A QModelRoleDataSpan is used as an abstraction over an array of QModelRoleData 对象。
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:
QVariant text = model->data(index, Qt::DisplayRole); QVariant decoration = model->data(index, Qt::DecorationRole); QVariant 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()
函数。
std::array<QModelRoleData, 3> roleData = { { QModelRoleData(Qt::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(). QModelRoleDataSpan span(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 对象。
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:
void MyModel::multiData(const QModelIndex &index, QModelRoleDataSpan roleDataSpan) const { for (QModelRoleData &roleData : roleDataSpan) { int role = roleData.role(); // ... obtain the data for index and role ... roleData.setData(result); } }
另请参阅 模型/视图编程 and QAbstractItemModel::multiData ().
[constexpr noexcept]
QModelRoleDataSpan::
QModelRoleDataSpan
()
Constructs an empty QModelRoleDataSpan. Its
data
() 会被设为
nullptr
, and its length to zero.
[constexpr noexcept]
QModelRoleDataSpan::
QModelRoleDataSpan
(
QModelRoleData
&
modelRoleData
)
Constructs an QModelRoleDataSpan spanning over modelRoleData , seen as a 1-element array.
[constexpr]
QModelRoleDataSpan::
QModelRoleDataSpan
(
QModelRoleData
*
modelRoleData
,
qsizetype
len
)
Constructs an QModelRoleDataSpan spanning over the array beginning at modelRoleData and with length len .
注意： The array must be kept alive as long as this object has not been destructed.
[constexpr noexcept(...)]
template <typename Container, QModelRoleDataSpan::if_compatible_container<Container> = true> QModelRoleDataSpan::
QModelRoleDataSpan
(
Container
&
c
)
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>
，
std::array<QModelRoleData, 10>
and so on.
注意： The container must be kept alive as long as this object has not been destructed.
注意： This function does not throw any exception when "noexcept(std::data(c)) && noexcept(std::size(c))" is true.
[constexpr noexcept]
QModelRoleData
*QModelRoleDataSpan::
begin
() const
Returns a pointer to the beginning of the span represented by this object.
[constexpr noexcept]
QModelRoleData
*QModelRoleDataSpan::
data
() const
Returns a pointer to the beginning of the span represented by this object.
[constexpr]
QVariant
*QModelRoleDataSpan::
dataForRole
(
int
role
) const
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.
注意： 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.
另请参阅 QModelRoleData::data ().
[constexpr noexcept]
QModelRoleData
*QModelRoleDataSpan::
end
() const
Returns a pointer to the imaginary element one past the end of the span represented by this object.
[constexpr noexcept]
qsizetype
QModelRoleDataSpan::
length
() const
Returns the length of the span represented by this object.
[constexpr noexcept]
qsizetype
QModelRoleDataSpan::
size
() const
Returns the length of the span represented by this object.
[constexpr]
QModelRoleData
&QModelRoleDataSpan::
operator[]
(
qsizetype
index
) const
Returns a modifiable reference to the QModelRoleData 在位置 index in the span.
注意： index must be a valid index for this span (0 <= index < size ()).