showMenu< T> function
Show a popup menu that contains the items
at position
.
If initialValue
is specified then the first item with a matching value
will be highlighted and the value of position
gives the rectangle whose
vertical center will be aligned with the vertical center of the highlighted
item (when possible).
If initialValue
is not specified then the top of the menu will be aligned
with the top of the position
rectangle.
In both cases, the menu position will be adjusted if necessary to fit on the screen.
Horizontally, the menu is positioned so that it grows in the direction that
has the most room. For example, if the position
describes a rectangle on
the left edge of the screen, then the left edge of the menu is aligned with
the left edge of the position
, and the menu grows to the right. If both
edges of the position
are equidistant from the opposite edge of the
screen, then the ambient Directionality is used as a tie-breaker,
preferring to grow in the reading direction.
The positioning of the initialValue
at the position
is implemented by
iterating over the items
to find the first whose
PopupMenuEntry.represents method returns true for initialValue
, and then
summing the values of PopupMenuEntry.height for all the preceding widgets
in the list.
The elevation
argument specifies the z-coordinate at which to place the
menu. The elevation defaults to 8, the appropriate elevation for popup
menus.
The context
argument is used to look up the Navigator and Theme for
the menu. It is only used when the method is called. Its corresponding
widget can be safely removed from the tree before the popup menu is closed.
The semanticLabel
argument is used by accessibility frameworks to
announce screen transitions when the menu is opened and closed. If this
label is not provided, it will default to
MaterialLocalizations.popupMenuLabel.
See also:
- PopupMenuItem, a popup menu entry for a single value.
- PopupMenuDivider, a popup menu entry that is just a horizontal line.
- CheckedPopupMenuItem, a popup menu item with a checkmark.
- PopupMenuButton, which provides an IconButton that shows a menu by calling this method automatically.
- SemanticsConfiguration.namesRoute, for a description of edge triggered semantics.
Implementation
Future<T> showMenu<T>({
@required BuildContext context,
RelativeRect position,
@required List<PopupMenuEntry<T>> items,
T initialValue,
double elevation = 8.0,
String semanticLabel,
}) {
assert(context != null);
assert(items != null && items.isNotEmpty);
assert(debugCheckHasMaterialLocalizations(context));
String label = semanticLabel;
switch (defaultTargetPlatform) {
case TargetPlatform.iOS:
label = semanticLabel;
break;
case TargetPlatform.android:
case TargetPlatform.fuchsia:
label = semanticLabel ?? MaterialLocalizations.of(context)?.popupMenuLabel;
}
return Navigator.push(context, _PopupMenuRoute<T>(
position: position,
items: items,
initialValue: initialValue,
elevation: elevation,
semanticLabel: label,
theme: Theme.of(context, shadowThemeOnly: true),
barrierLabel: MaterialLocalizations.of(context).modalBarrierDismissLabel,
));
}