Initializes the Widget ui.

def __initialize_ui(self):
        """
        Initializes the Widget ui.
        """

        self.__clear_button.setCursor(Qt.ArrowCursor)
        if self.__ui_clear_image and self.__ui_clear_clicked_image:
            pixmap = QPixmap(self.__ui_clear_image)
            clicked_pixmap = QPixmap(self.__ui_clear_clicked_image)
            self.__clear_button.setIcon(QIcon(pixmap))
            self.__clear_button.setMaximumSize(pixmap.size())

            # Signals / Slots.
            self.__clear_button.pressed.connect(functools.partial(self.__clear_button.setIcon, QIcon(clicked_pixmap)))
            self.__clear_button.released.connect(functools.partial(self.__clear_button.setIcon, QIcon(pixmap)))
        else:
            self.__clear_button.setText("Clear")

        self.__set_style_sheet()

        frame_width = self.style().pixelMetric(QStyle.PM_DefaultFrameWidth)
        self.setMinimumSize(
            max(self.minimumSizeHint().width(), self.__clear_button.sizeHint().height() + frame_width * 2),
            max(self.minimumSizeHint().height(), self.__clear_button.sizeHint().height() + frame_width * 2))

        self.__completer.setCaseSensitivity(Qt.CaseInsensitive)
        self.__completer.setCompletionMode(QCompleter.UnfilteredPopupCompletion)
        self.__completer.setMaxVisibleItems(self.__completer_visible_items_count)