feat: add QFlowLayout, for variable width widgets (#271)

* feat: add QLayout

* add to docs

docs/widgets/index.md

@@ -33,3 +33,4 @@ The following are QWidget subclasses:
 | Widget                          | Description           |
 | -----------                     | --------------------- |
 | [`QCollapsible`](./qcollapsible.md)              | A collapsible widget to hide and unhide child widgets. |
+| [`QFlowLayout`](./qflowlayout.md)                | A layout that rearranges items based on parent width. |

docs/widgets/qflowlayout.md

@@ -0,0 +1,29 @@
+# QFlowLayout
+
+QLayout that rearranges items based on parent width.
+
+```python
+from qtpy.QtWidgets import QApplication, QPushButton, QWidget
+
+from superqt import QFlowLayout
+
+app = QApplication([])
+
+wdg = QWidget()
+
+layout = QFlowLayout(wdg)
+layout.addWidget(QPushButton("Short"))
+layout.addWidget(QPushButton("Longer"))
+layout.addWidget(QPushButton("Different text"))
+layout.addWidget(QPushButton("More text"))
+layout.addWidget(QPushButton("Even longer button text"))
+
+wdg.setWindowTitle("Flow Layout")
+wdg.show()
+
+app.exec()
+```
+
+{{ show_widget(350) }}
+
+{{ show_members('superqt.QFlowLayout') }}

examples/flow_layout.py

@@ -0,0 +1,19 @@
+from qtpy.QtWidgets import QApplication, QPushButton, QWidget
+
+from superqt import QFlowLayout
+
+app = QApplication([])
+
+wdg = QWidget()
+
+layout = QFlowLayout(wdg)
+layout.addWidget(QPushButton("Short"))
+layout.addWidget(QPushButton("Longer"))
+layout.addWidget(QPushButton("Different text"))
+layout.addWidget(QPushButton("More text"))
+layout.addWidget(QPushButton("Even longer button text"))
+
+wdg.setWindowTitle("Flow Layout")
+wdg.show()
+
+app.exec()

src/superqt/__init__.py

@@ -23,7 +23,12 @@
     QRangeSlider,
 )
 from .spinbox import QLargeIntSpinBox
-from .utils import QMessageHandler, ensure_main_thread, ensure_object_thread
+from .utils import (
+    QFlowLayout,
+    QMessageHandler,
+    ensure_main_thread,
+    ensure_object_thread,
+)
 
 __all__ = [
     "QCollapsible",
@@ -34,6 +39,7 @@
     "QElidingLabel",
     "QElidingLineEdit",
     "QEnumComboBox",
+    "QFlowLayout",
     "QIconifyIcon",
     "QLabeledDoubleRangeSlider",
     "QLabeledDoubleSlider",

src/superqt/utils/__init__.py

@@ -7,6 +7,7 @@
     "CodeSyntaxHighlight",
     "FunctionWorker",
     "GeneratorWorker",
+    "QFlowLayout",
     "QMessageHandler",
     "QSignalDebouncer",
     "QSignalThrottler",
@@ -27,6 +28,7 @@
 from ._code_syntax_highlight import CodeSyntaxHighlight
 from ._ensure_thread import ensure_main_thread, ensure_object_thread
 from ._errormsg_context import exceptions_as_dialog
+from ._flow_layout import QFlowLayout
 from ._img_utils import qimage_to_array
 from ._message_handler import QMessageHandler
 from ._misc import signals_blocked

src/superqt/utils/_flow_layout.py

@@ -0,0 +1,183 @@
+from __future__ import annotations
+
+from qtpy.QtCore import QPoint, QRect, QSize, Qt
+from qtpy.QtWidgets import QLayout, QLayoutItem, QSizePolicy, QStyle, QWidget
+
+
+class QFlowLayout(QLayout):
+    """Layout that handles different window sizes.
+
+    The widget placement changes depending on the width of the application window.
+
+    Code translated from C++ at:
+    <https://code.qt.io/cgit/qt/qtbase.git/tree/examples/widgets/layouts/flowlayout>
+
+    described at: <https://doc.qt.io/qt-6/qtwidgets-layouts-flowlayout-example.html>
+
+    See also: <https://doc.qt.io/qt-6/layout.html>
+
+    Parameters
+    ----------
+    parent : QWidget, optional
+        The parent widget, by default None
+    """
+
+    def __init__(self, parent: QWidget | None = None) -> None:
+        super().__init__(parent)
+
+        self._item_list: list[QLayoutItem] = []
+        self._h_space = -1
+        self._v_space = -1
+
+    def __del__(self) -> None:
+        while item := self.takeAt(0):
+            del item
+
+    def addItem(self, item: QLayoutItem | None) -> None:
+        """Add an item to the layout."""
+        if item:
+            self._item_list.append(item)
+
+    def setHorizontalSpacing(self, space: int | None) -> None:
+        """Set the horizontal spacing.
+
+        If None or -1, the spacing is set to the default value based on the style
+        of the parent widget.
+        """
+        self._h_space = -1 if space is None else space
+
+    def horizontalSpacing(self) -> int:
+        """Return the horizontal spacing."""
+        if self._h_space >= 0:
+            return self._h_space
+        return self._smartSpacing(QStyle.PixelMetric.PM_LayoutHorizontalSpacing)
+
+    def setVerticalSpacing(self, space: int | None) -> None:
+        """Set the vertical spacing.
+
+        If None or -1, the spacing is set to the default value based on the style
+        of the parent widget.
+        """
+        self._v_space = -1 if space is None else space
+
+    def verticalSpacing(self) -> int:
+        """Return the vertical spacing."""
+        if self._v_space >= 0:
+            return self._v_space
+        return self._smartSpacing(QStyle.PixelMetric.PM_LayoutVerticalSpacing)
+
+    def expandingDirections(self) -> Qt.Orientation:
+        """Return the expanding directions.
+
+        These are the Qt::Orientations in which the layout can make use of more space
+        than its sizeHint().
+        """
+        return Qt.Orientation.Horizontal
+
+    def hasHeightForWidth(self) -> bool:
+        """Return whether the layout handles height for width."""
+        return True
+
+    def heightForWidth(self, width: int) -> int:
+        """Return the height for a given width.
+
+        `heightForWidth()` passes the width on to _doLayout() which in turn uses the
+        width as an argument for the layout rect, i.e., the bounds in which the items
+        are laid out. This rect does not include the layout margin().
+        """
+        return self._doLayout(QRect(0, 0, width, 0), True)
+
+    def count(self) -> int:
+        """Return the number of items in the layout."""
+        return len(self._item_list)
+
+    def itemAt(self, index: int) -> QLayoutItem | None:
+        """Return the item at the given index, or None if the index is out of range."""
+        try:
+            return self._item_list[index]
+        except IndexError:
+            return None
+
+    def minimumSize(self) -> QSize:
+        """Return the minimum size of the layout."""
+        size = QSize()
+        for item in self._item_list:
+            size = size.expandedTo(item.minimumSize())
+
+        margins = self.contentsMargins()
+        size += QSize(
+            margins.left() + margins.right(), margins.top() + margins.bottom()
+        )
+        return size
+
+    def setGeometry(self, rect: QRect) -> None:
+        """Set the geometry of the layout.
+
+        This triggers a re-layout of the items.
+        """
+        super().setGeometry(rect)
+        self._doLayout(rect)
+
+    def sizeHint(self) -> QSize:
+        """Return the size hint of the layout."""
+        return self.minimumSize()
+
+    def takeAt(self, index: int) -> QLayoutItem | None:
+        """Remove and return the item at the given index.  Or return None."""
+        if 0 <= index < len(self._item_list):
+            return self._item_list.pop(index)
+        return None
+
+    def _doLayout(self, rect: QRect, test_only: bool = False) -> int:
+        """Arrange the items in the layout.
+
+        If test_only is True, the items are not actually laid out, but the height
+        that the layout would have with the given width is returned.
+        """
+        left, top, right, bottom = self.getContentsMargins()
+        effective_rect = rect.adjusted(left, top, -right, -bottom)  # type: ignore
+        x = effective_rect.x()
+        y = effective_rect.y()
+        line_height = 0
+
+        for item in self._item_list:
+            if (wid := item.widget()) and (style := wid.style()):
+                space_x = self.horizontalSpacing()
+                space_y = self.verticalSpacing()
+                if space_x == -1:
+                    space_x = style.layoutSpacing(
+                        QSizePolicy.ControlType.PushButton,
+                        QSizePolicy.ControlType.PushButton,
+                        Qt.Orientation.Horizontal,
+                    )
+                if space_y == -1:
+                    space_y = style.layoutSpacing(
+                        QSizePolicy.ControlType.PushButton,
+                        QSizePolicy.ControlType.PushButton,
+                        Qt.Orientation.Vertical,
+                    )
+
+                # next_x is the x-coordinate of the right edge of the item
+                next_x = x + item.sizeHint().width() + space_x
+                # if the item is not the first one in a line, add the spacing
+                # to the left of it
+                if next_x - space_x > effective_rect.right() and line_height > 0:
+                    x = effective_rect.x()
+                    y = y + line_height + space_y
+                    next_x = x + item.sizeHint().width() + space_x
+                    line_height = 0
+
+                # if this is not a test run, move the item to its proper place
+                if not test_only:
+                    item.setGeometry(QRect(QPoint(x, y), item.sizeHint()))
+
+                x = next_x
+                line_height = max(line_height, item.sizeHint().height())
+
+        return y + line_height - rect.y() + bottom
+
+    def _smartSpacing(self, pm: QStyle.PixelMetric) -> int:
+        """Return the smart spacing based on the style of the parent widget."""
+        if isinstance(parent := self.parent(), QWidget) and (style := parent.style()):
+            return style.pixelMetric(pm, None, parent)
+        return -1

tests/test_flow_layout.py

@@ -0,0 +1,27 @@
+from typing import Any
+
+from qtpy.QtWidgets import QPushButton, QWidget
+
+from superqt import QFlowLayout
+
+
+def test_flow_layout(qtbot: Any) -> None:
+    wdg = QWidget()
+    qtbot.addWidget(wdg)
+
+    layout = QFlowLayout(wdg)
+    layout.addWidget(QPushButton("Short"))
+    layout.addWidget(QPushButton("Longer"))
+    layout.addWidget(QPushButton("Different text"))
+    layout.addWidget(QPushButton("More text"))
+    layout.addWidget(QPushButton("Even longer button text"))
+
+    wdg.setWindowTitle("Flow Layout")
+    wdg.show()
+
+    assert layout.expandingDirections()
+    assert layout.heightForWidth(200) > layout.heightForWidth(400)
+    assert layout.count() == 5
+    assert layout.itemAt(0).widget().text() == "Short"
+    layout.takeAt(0)
+    assert layout.count() == 4