flutter_flutter/packages/flutter/test/painting/image_cache_binding_test.dart

// Copyright 2014 The Flutter 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:ui' as ui;

import 'package:flutter/foundation.dart';
import 'package:flutter/painting.dart';
import 'package:flutter/scheduler.dart';
import 'package:flutter/services.dart';

import 'package:flutter_test/flutter_test.dart';

void main() {
  test('PaintingBinding with memory pressure before initInstances', () async {
    // Observed in devicelab: the device sends a memory pressure event
    // to us before the binding is initialized, so as soon as the
    // ServicesBinding's initInstances sets up the callbacks, we get a
    // call. Previously this would happen synchronously during
    // initInstances (and before the imageCache was initialized, which
    // was a problem), but now it happens asynchronously just after.

    ui.channelBuffers.push(SystemChannels.system.name, SystemChannels.system.codec.encodeMessage(<String, dynamic>{
      'type': 'memoryPressure',
    }), (ByteData? responseData) {
      // The result is: SystemChannels.system.codec.decodeMessage(responseData)
      // ...but we ignore it for the purposes of this test.
    });

    final TestPaintingBinding binding = TestPaintingBinding();
    expect(binding._handled, isFalse);
    expect(binding.imageCache, isNotNull);
    expect(binding.imageCache.currentSize, 0);

    await null; // allow microtasks to run
    expect(binding._handled, isTrue);
  });
}

class TestPaintingBinding extends BindingBase with SchedulerBinding, ServicesBinding, PaintingBinding {
  @override
  void handleMemoryPressure() {
    super.handleMemoryPressure();
    _handled = true;
  }

  bool _handled = false;
}