snap_scrolling_test.dart

// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:flutter_test/flutter_test.dart';
import 'package:flutter/widgets.dart';
import 'package:test/test.dart';

const double itemExtent = 200.0;
Axis scrollDirection = Axis.vertical;
GlobalKey scrollableListKey;

Widget buildItem(int item) {
  return new Container(
    width: itemExtent,
    height: itemExtent,
    child: new Text(item.toString())
  );
}

double snapOffsetCallback(double offset, Size size) {
  return (offset / itemExtent).floor() * itemExtent;
}

Widget buildFrame() {
  scrollableListKey = new GlobalKey();
  return new Center(
    child: new Container(
      height: itemExtent * 2.0,
      child: new ScrollableList(
        key: scrollableListKey,
        snapOffsetCallback: snapOffsetCallback,
        scrollDirection: scrollDirection,
        itemExtent: itemExtent,
        children: <int>[0, 1, 2, 3, 4, 5, 7, 8, 9].map(buildItem)
      )
    )
  );
}

ScrollableState get scrollableState => scrollableListKey.currentState;

double get scrollOffset =>  scrollableState.scrollOffset;
void set scrollOffset(double value) {
  scrollableState.scrollTo(value);
}

Future<Null> fling(double velocity) {
  return scrollableState.fling(velocity);
}

void main() {
  testWidgets('ScrollableList snap scrolling, fling(0.8)', (WidgetTester tester) {
    tester.pumpWidget(buildFrame());

    scrollOffset = 0.0;
    tester.pump();
    expect(scrollOffset, 0.0);

    Duration dt = const Duration(seconds: 2);

    fling(0.8);
    tester.pump(); // Start the scheduler at 0.0
    tester.pump(dt);
    expect(scrollOffset, closeTo(200.0, 1.0));

    scrollOffset = 0.0;
    tester.pump();
    expect(scrollOffset, 0.0);

    fling(2.0);
    tester.pump();
    tester.pump(dt);
    expect(scrollOffset, closeTo(400.0, 1.0));

    scrollOffset = 400.0;
    tester.pump();
    expect(scrollOffset, 400.0);

    fling(-0.8);
    tester.pump();
    tester.pump(dt);
    expect(scrollOffset, closeTo(0.0, 1.0));

    scrollOffset = 800.0;
    tester.pump();
    expect(scrollOffset, 800.0);

    fling(-2.0);
    tester.pump();
    tester.pump(dt);
    expect(scrollOffset, closeTo(200.0, 1.0));

    scrollOffset = 800.0;
    tester.pump();
    expect(scrollOffset, 800.0);

    bool completed = false;
    fling(-2.0).then((_) {
      completed = true;
      expect(scrollOffset, closeTo(200.0, 1.0));
    });
    tester.pump();
    tester.pump(dt);
    expect(completed, true);
  });
}