Extracting Information from the View

The presenter will need a way to obtain information from the view. This can be done by get methods, as with normal classes. Here is a simple example of how a get method for the view can be used.

from qtpy.QtWidgets import QHBoxLayout, QLabel, QLineEdit, QPushButton, QVBoxLayout, QWidget
from typing import Union


class View(QWidget):

    def __init__(self, parent: Union[QWidget, None]=None):
        super().__init__(parent)
        self.setWindowTitle("view tutorial")

        # A presenter will be subscribed to the view later
        self._presenter = None

        self._button = QPushButton("Hi", self)
        self._button.setStyleSheet("background-color:lightgrey")
        # connect button to signal
        self._button.clicked.connect(self._button_clicked)

        self._label = QLabel()
        self._label.setText("Button")

        # add widgets to layout
        self._sub_layout = QHBoxLayout()
        self._sub_layout.addWidget(self._label)
        self._sub_layout.addWidget(self._button)

        grid = QVBoxLayout(self)
        grid.addLayout(self.sub_layout)

        self._value = QLineEdit()
        grid.addWidget(self._value)

        # set the layout for the view widget
        self.setLayout(grid)

    def subscribe_presenter(self, presenter) -> None:
        # Subscribe the presenter to the view so we do not need to
        # make a Qt connection between the presenter and view
        self._presenter = presenter

    def _button_clicked(self) -> None:
        print("hello from view")
        self._presenter.handle_button_clicked()

    def get_value(self) -> float:
        return float(self._value.text())

The last function get_value returns the value of the line edit. Since text() returns a string the output is type cast into a float.

The presenter has the following code added to the handle_button_clicked method:

value = self._view.get_value()
print(f"Value is {value}")

which gets the value from the view and then prints it to the screen.