You can manually hit test RenderBox and extract a specific RenderObject of your choice.
We could for example add the following renderobject above our buttons:
class Foo extends SingleChildRenderObjectWidget {
final int index;
Foo({Widget child, this.index, Key key}) : super(child: child, key: key);
@override
RenderObject createRenderObject(BuildContext context) {
return _Foo()..index = index;
}
@override
void updateRenderObject(BuildContext context, _Foo renderObject) {
renderObject..index = index;
}
}
class _Foo extends RenderProxyBox {
int index;
}
Then use a Listener to extract all _Foo
found under the pointer.
Here's a full application using this principle:
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(primarySwatch: Colors.blue),
home: Grid(),
);
}
}
class Grid extends StatefulWidget {
@override
GridState createState() {
return new GridState();
}
}
class GridState extends State<Grid> {
final Set<int> selectedIndexes = Set<int>();
final key = GlobalKey();
final Set<_Foo> _trackTaped = Set<_Foo>();
_detectTapedItem(PointerEvent event) {
final RenderBox box = key.currentContext.findRenderObject();
final result = BoxHitTestResult();
Offset local = box.globalToLocal(event.position);
if (box.hitTest(result, position: local)) {
for (final hit in result.path) {
/// temporary variable so that the [is] allows access of [index]
final target = hit.target;
if (target is _Foo && !_trackTaped.contains(target)) {
_trackTaped.add(target);
_selectIndex(target.index);
}
}
}
}
_selectIndex(int index) {
setState(() {
selectedIndexes.add(index);
});
}
@override
Widget build(BuildContext context) {
return Listener(
onPointerDown: _detectTapedItem,
onPointerMove: _detectTapedItem,
onPointerUp: _clearSelection,
child: GridView.builder(
key: key,
itemCount: 6,
physics: NeverScrollableScrollPhysics(),
gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 3,
childAspectRatio: 1.0,
crossAxisSpacing: 5.0,
mainAxisSpacing: 5.0,
),
itemBuilder: (context, index) {
return Foo(
index: index,
child: Container(
color: selectedIndexes.contains(index) ? Colors.red : Colors.blue,
),
);
},
),
);
}
void _clearSelection(PointerUpEvent event) {
_trackTaped.clear();
setState(() {
selectedIndexes.clear();
});
}
}
class Foo extends SingleChildRenderObjectWidget {
final int index;
Foo({Widget child, this.index, Key key}) : super(child: child, key: key);
@override
_Foo createRenderObject(BuildContext context) {
return _Foo()..index = index;
}
@override
void updateRenderObject(BuildContext context, _Foo renderObject) {
renderObject..index = index;
}
}
class _Foo extends RenderProxyBox {
int index;
}
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