fix a dropdown button menu position bug (#89199)
diff --git a/packages/flutter/lib/src/material/dropdown.dart b/packages/flutter/lib/src/material/dropdown.dart
index cf05969..265410e 100644
--- a/packages/flutter/lib/src/material/dropdown.dart
+++ b/packages/flutter/lib/src/material/dropdown.dart
@@ -517,7 +517,10 @@
// selected item is aligned with the button's vertical center, as far as
// that's possible given availableHeight.
_MenuLimits getMenuLimits(Rect buttonRect, double availableHeight, int index) {
- final double maxMenuHeight = availableHeight - 2.0 * _kMenuItemHeight;
+ double computedMaxHeight = availableHeight - 2.0 * _kMenuItemHeight;
+ if (menuMaxHeight != null) {
+ computedMaxHeight = math.min(computedMaxHeight, menuMaxHeight!);
+ }
final double buttonTop = buttonRect.top;
final double buttonBottom = math.min(buttonRect.bottom, availableHeight);
final double selectedItemOffset = getItemOffset(index);
@@ -535,8 +538,8 @@
preferredMenuHeight += itemHeights.reduce((double total, double height) => total + height);
// If there are too many elements in the menu, we need to shrink it down
- // so it is at most the maxMenuHeight.
- final double menuHeight = math.min(maxMenuHeight, preferredMenuHeight);
+ // so it is at most the computedMaxHeight.
+ final double menuHeight = math.min(computedMaxHeight, preferredMenuHeight);
double menuBottom = menuTop + menuHeight;
// If the computed top or bottom of the menu are outside of the range
@@ -544,14 +547,21 @@
// than the button height and the button is at the very bottom or top of the
// screen, the menu will be aligned with the bottom or top of the button
// respectively.
- if (menuTop < topLimit)
+ if (menuTop < topLimit) {
menuTop = math.min(buttonTop, topLimit);
+ menuBottom = menuTop + menuHeight;
+ }
if (menuBottom > bottomLimit) {
menuBottom = math.max(buttonBottom, bottomLimit);
menuTop = menuBottom - menuHeight;
}
+ if (menuBottom - itemHeights[selectedIndex] / 2.0 < buttonBottom - buttonRect.height / 2.0) {
+ menuBottom = buttonBottom - buttonRect.height / 2.0 + itemHeights[selectedIndex] / 2.0;
+ menuTop = menuBottom - menuHeight;
+ }
+
double scrollOffset = 0;
// If all of the menu items will not fit within availableHeight then
// compute the scroll offset that will line the selected menu item up
@@ -559,7 +569,7 @@
// shown - subsequently we leave the scroll offset where the user left
// it. This scroll offset is only accurate for fixed height menu items
// (the default).
- if (preferredMenuHeight > maxMenuHeight) {
+ if (preferredMenuHeight > computedMaxHeight) {
// The offset should be zero if the selected item is in view at the beginning
// of the menu. Otherwise, the scroll offset should center the item if possible.
scrollOffset = math.max(0.0, selectedItemOffset - (buttonTop - menuTop));
@@ -568,6 +578,7 @@
scrollOffset = math.min(scrollOffset, preferredMenuHeight - menuHeight);
}
+ assert(menuHeight == menuBottom - menuTop);
return _MenuLimits(menuTop, menuBottom, menuHeight, scrollOffset);
}
}
diff --git a/packages/flutter/test/material/dropdown_test.dart b/packages/flutter/test/material/dropdown_test.dart
index 20a9d43..7543ccb 100644
--- a/packages/flutter/test/material/dropdown_test.dart
+++ b/packages/flutter/test/material/dropdown_test.dart
@@ -3127,6 +3127,29 @@
expect(menuHeight, defaultMenuHeight);
});
+ // Regression test for https://github.com/flutter/flutter/issues/89029
+ testWidgets('menu position test with `menuMaxHeight`', (WidgetTester tester) async {
+ final Key buttonKey = UniqueKey();
+ await tester.pumpWidget(buildFrame(
+ buttonKey: buttonKey,
+ value: '6',
+ items: List<String>.generate(/*length=*/64, (int index) => index.toString()),
+ onChanged: onChanged,
+ menuMaxHeight: 2 * kMinInteractiveDimension,
+ ));
+
+ await tester.tap(find.text('6'));
+ await tester.pumpAndSettle();
+
+ final RenderBox menuBox = tester.renderObject(find.byType(ListView));
+ final RenderBox buttonBox = tester.renderObject(find.byKey(buttonKey));
+ // The menu's bottom should align with the drop-button's bottom.
+ expect(
+ menuBox.localToGlobal(menuBox.paintBounds.bottomCenter).dy,
+ buttonBox.localToGlobal(buttonBox.paintBounds.bottomCenter).dy,
+ );
+ });
+
// Regression test for https://github.com/flutter/flutter/issues/76614
testWidgets('Do not crash if used in very short screen', (WidgetTester tester) async {
// The default item height is 48.0 pixels and needs two items padding since
