QTableView中的虚拟列？

Question

我开始学习Qt4模型/视图编程,我有初学者的问题.

我有简单的应用程序,显示sqlite表QTableView:

class Model(QtSql.QSqlTableModel):
    def __init__(self, parent=None):
        super(Model, self).__init__(parent)
        self.setEditStrategy(QtSql.QSqlTableModel.OnFieldChange)

        self.setTable("test")
        self.select()

class App(QtGui.QMainWindow):
    def __init__(self, model):
        QtGui.QMainWindow.__init__(self)

        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        self.ui.tableView.setModel(model)

if __name__ == "__main__":
    myDb = QtSql.QSqlDatabase.addDatabase("QSQLITE")
    myDb.setDatabaseName("test.db")

    if not myDb.open():
        print 'FIXME'

    model = Model()

    app = QtGui.QApplication(sys.argv)
    window = App(model)
    window.show()
    sys.exit(app.exec_())

这里数据库的样子如下:

sqlite> create table test (a INTEGER, b INTEGER, c STRING);
sqlite> insert into test VALUES(1, 2, "xxx");
sqlite> insert into test VALUES(6, 7, "yyy");

所以我得到了类似的东西:

+---+---+-----+
| a | b |  c  |
+---+---+-----+
| 1 | 2 | xxx |
+---+---+-----+
| 6 | 7 | yyy |
+---+---+-----+

是否有可能修改Model为QTableView像虚拟列？例如:

+---+---+-----+-----+
| a | b | sum |  c  |
+---+---+-----+-----+
| 1 | 2 |  3  | xxx |
+---+---+-----+-----+
| 6 | 7 | 13  | yyy |
+---+---+-----+-----+

或许我应该以其他方式做到这一点？

Answer 1

是的,你可以这样做.虽然@ BrtH的答案是相关的,但模型很棘手,很容易丢失.所以我认为更好的案例会更好.

就个人而言,我使用的是代理模型QAbstractProxyModel.但是,在你的情况下,重新实现QSqlTableModel也是可行的.以下是您的目标实现.请注意,您必须了解模型/视图方法的基础知识,以便了解每种方法的作用.

class Model(QtSql.QSqlTableModel):
    def __init__(self, parent=None):
        super(Model, self).__init__(parent)
        self.setEditStrategy(QtSql.QSqlTableModel.OnFieldChange)

        self.setTable("test")
        self.select()


    def columnCount(self, parent=QtCore.QModelIndex()):
        # this is probably obvious
        # since we are adding a virtual column, we need one more column
        return super(Model, self).columnCount()+1


    def data(self, index, role=QtCore.Qt.DisplayRole):
        if role == QtCore.Qt.DisplayRole and index.column()==2:
            # 2nd column is our virtual column.
            # if we are there, we need to calculate and return the value
            # we take the first two columns, get the data, turn it to integer and sum them
            # [0] at the end is necessary because pyqt returns value and a bool
            # http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/qvariant.html#toInt
            return sum(self.data(self.index(index.row(), i)).toInt()[0] for i in range(2))
        if index.column() > 2:
            # if we are past 2nd column, we need to shift it to left by one
            # to get the real value
            index = self.index(index.row(), index.column()-1)
        # get the value from base implementation
        return super(Model, self).data(index, role)


    def headerData(self, section, orientation, role=QtCore.Qt.DisplayRole):
        # this is similar to `data`
        if section==2 and orientation==QtCore.Qt.Horizontal and role==QtCore.Qt.DisplayRole:
            return 'Sum'
        if section > 2 and orientation==QtCore.Qt.Horizontal:
            section -= 1
        return super(Model, self).headerData(section, orientation, role)


    def flags(self, index):
        # since 2nd column is virtual, it doesn't make sense for it to be Editable
        # other columns can be Editable (default for QSqlTableModel)
        if index.column()==2:
            return QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEnabled
        return QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsEditable


    def setData(self, index, data, role):
        # similar to data.
        # we need to be careful when setting data (after edit)
        # if column is after 2, it is actually the column before that
        if index.column() > 2:
            index = self.index(index.row(), index.column()-1)
        return super(Model, self).setData(index, data, role)