Conway’s Game of Life example shows how the QML TableView type can be used to display a C++ model that the user can pan around.
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TableView { id: tableView anchors.fill: parent rowSpacing: 1 columnSpacing: 1 ScrollBar.horizontal: ScrollBar {} ScrollBar.vertical: ScrollBar {} delegate: Rectangle { id: cell implicitWidth: 15 implicitHeight: 15 required property var model required property bool value color: value ? "#f3f3f4" : "#b5b7bf" MouseArea { anchors.fill: parent onClicked: parent.model.value = !parent.value } }
范例使用
TableView
component to display a grid of cells. Each of these cells is drawn on the screen by the
TableView
’s delegate, which is a Rectangle QML component. We read the cell’s value and we change it using
model.value
when the user clicks it.
contentX: (contentWidth - width) / 2; contentY: (contentHeight - height) / 2;
当应用程序启动时，
TableView
is scrolled to its center by using its
contentX
and
contentY
properties to update the scroll position, and the
contentWidth
and
contentHeight
to compute where the view should be scrolled to.
model: GameOfLifeModel { id: gameOfLifeModel }
class GameOfLifeModel : public QAbstractTableModel { Q_OBJECT QML_ELEMENT Q_ENUMS(Roles) public: enum Roles { CellRole }; QHash<int, QByteArray> roleNames() const override { return { { CellRole, "value" } }; } explicit GameOfLifeModel(QObject *parent = nullptr); int rowCount(const QModelIndex &parent = QModelIndex()) const override; int columnCount(const QModelIndex &parent = QModelIndex()) const override; QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override; bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override; Qt::ItemFlags flags(const QModelIndex &index) const override; Q_INVOKABLE void nextStep(); Q_INVOKABLE bool loadFile(const QString &fileName); Q_INVOKABLE void loadPattern(const QString &plainText); Q_INVOKABLE void clear(); private: static constexpr int width = 256; static constexpr int height = 256; static constexpr int size = width * height; using StateContainer = std::array<bool, size>; StateContainer m_currentState; int cellNeighborsCount(const QPoint &cellCoordinates) const; static bool areCellCoordinatesValid(const QPoint &coordinates); static QPoint cellCoordinatesFromIndex(int cellIndex); static std::size_t cellIndex(const QPoint &coordinates); };
GameOfLifeModel
class extends
QAbstractTableModel
so it can be used as the model of our
TableView
component. Therefore, it needs to implement some functions so the
TableView
component can interact with the model. As you can see in the
private
part of the class, the model uses a fixed-size array to store the current state of all the cells. We also use the
QML_ELEMENT
macro in order to expose the class to QML.
int GameOfLifeModel::rowCount(const QModelIndex &parent) const { if (parent.isValid()) return 0; return height; } int GameOfLifeModel::columnCount(const QModelIndex &parent) const { if (parent.isValid()) return 0; return width; }
在这里，
rowCount
and
columnCount
methods are implemented so the
TableView
component can know the size of the table. It simply returns the values of the
width
and
height
constants.
QVariant GameOfLifeModel::data(const QModelIndex &index, int role) const { if (!index.isValid() || role != CellRole) return QVariant(); return QVariant(m_currentState[cellIndex({index.column(), index.row()})]); }
This method is called when the
TableView
component requests some data from the model. In our example, we only have one piece of data by cell: whether it is alive or not. This information is represented by the
CellRole
value of the
Roles
enum in our C++ code; this corresponds to the
value
property in the QML code (the link between these two is made by the
roleNames()
function of our C++ class).
GameOfLifeModel
class can identify which cell was the data requested from with the
index
parameter, which is a
QModelIndex
that contains a row and a column.
bool GameOfLifeModel::setData(const QModelIndex &index, const QVariant &value, int role) { if (role != CellRole || data(index, role) == value) return false; m_currentState[cellIndex({index.column(), index.row()})] = value.toBool(); emit dataChanged(index, index, {role}); return true; }
setData
method is called when a property’s value is set from the QML interface: in our example, it toggles a cell’s state when it is clicked. In the same way as the
data()
function does, this method receives an
index
和
role
parameter. Additionally, the new value is passed as a
QVariant
, that we convert to a boolean using the
toBool
函数。
When we update the internal state of our model object, we need to emit a
dataChanged
signal to tell the
TableView
component that it needs to update the displayed data. In this case, only the cell that was clicked is affected, thus the range of the table that has to be updated begins and ends at the cell’s index.
void GameOfLifeModel::nextStep() { StateContainer newValues; for (std::size_t i = 0; i < size; ++i) { bool currentState = m_currentState[i]; int cellNeighborsCount = this->cellNeighborsCount(cellCoordinatesFromIndex(static_cast<int>(i))); newValues[i] = currentState == true ? cellNeighborsCount == 2 || cellNeighborsCount == 3 : cellNeighborsCount == 3; } m_currentState = std::move(newValues); emit dataChanged(index(0, 0), index(height - 1, width - 1), {CellRole}); }
This function can be called directly from the QML code, because it contains the
Q_INVOKABLE
macro in its definition. It plays an iteration of the game, either when the user clicks the
下一
button or when the Timer emits a
triggered()
信号。
Following the Conway’s Game of Life rules, a new state is computed for each cell depending on the current state of its neighbors. When the new state has been computed for the whole grid, it replaces the current state and a dataChanged signal is emitted for the whole table.
bool GameOfLifeModel::loadFile(const QString &fileName) { QFile file(fileName); if (!file.open(QIODevice::ReadOnly)) return false; QTextStream in(&file); loadPattern(in.readAll()); return true; } void GameOfLifeModel::loadPattern(const QString &plainText) { clear(); QStringList rows = plainText.split("\n"); QSize patternSize(0, rows.count()); for (QString row : rows) { if (row.size() > patternSize.width()) patternSize.setWidth(row.size()); } QPoint patternLocation((width - patternSize.width()) / 2, (height - patternSize.height()) / 2); for (int y = 0; y < patternSize.height(); ++y) { const QString line = rows[y]; for (int x = 0; x < line.length(); ++x) { QPoint cellPosition(x + patternLocation.x(), y + patternLocation.y()); m_currentState[cellIndex(cellPosition)] = line[x] == 'O'; } } emit dataChanged(index(0, 0), index(height - 1, width - 1), {CellRole}); }
When the application opens, a pattern is loaded to demonstrate how
Conway’s Game of Life
works. These two functions load the file where the pattern is stored and parse it. As in the
nextStep
function, a
dataChanged
signal is emitted for the whole table once the pattern has been fully loaded.
