68 lines
2.3 KiB
Dart
68 lines
2.3 KiB
Dart
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'dart:convert';
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import 'dart:ui' as ui show Codec;
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import 'package:flutter/foundation.dart';
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import 'package:flutter/material.dart';
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/// An animated GIF image with 3 1x1 pixel frames (a red, green, and blue
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/// frames). The GIF animates forever, and each frame has a 100ms delay.
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const String kAnimatedGif = 'R0lGODlhAQABAKEDAAAA//8AAAD/AP///yH/C05FVFNDQVBFMi'
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'4wAwEAAAAh+QQACgD/ACwAAAAAAQABAAACAkwBACH5BAAKAP8A'
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'LAAAAAABAAEAAAICVAEAIfkEAAoA/wAsAAAAAAEAAQAAAgJEAQ'
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'A7';
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/// A 50x50 blue square png
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const String kBlueSquare = 'iVBORw0KGgoAAAANSUhEUgAAADIAAAAyCAYAAAAeP4ixAAAASEl'
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'EQVR42u3PMQ0AMAgAsGFjL/4tYQU08JLWQSN/9TsgRERERERERE'
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'REREREREREREREREREREREREREREREREREREREREQ2BgNuaUcSj'
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'uqqAAAAAElFTkSuQmCC';
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/// A 10x10 grid of animated looping placeholder gifts that fade into a
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/// blue square.
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class AnimatedPlaceholderPage extends StatelessWidget {
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@override
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Widget build(BuildContext context) {
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return GridView.builder(
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itemCount: 100,
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gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 10),
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itemBuilder: (BuildContext context, int index) {
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return FadeInImage(
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placeholder: const DelayedBase64Image(Duration.zero, kAnimatedGif),
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image: DelayedBase64Image(Duration(milliseconds: 100 * index), kBlueSquare),
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);
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},
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);
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}
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}
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int _key = 0;
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/// An image provider that is always unique from other DelayedBase64Images and
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/// simulates a delay in loading.
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class DelayedBase64Image extends ImageProvider<int> {
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const DelayedBase64Image(this.delay, this.data);
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final String data;
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final Duration delay;
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@override
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Future<int> obtainKey(ImageConfiguration configuration) {
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return SynchronousFuture<int>(_key++);
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}
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@override
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ImageStreamCompleter load(int key, DecoderCallback decode) {
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return MultiFrameImageStreamCompleter(
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codec: Future<ui.Codec>.delayed(
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delay,
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() => decode(base64.decode(data)),
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),
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scale: 1.0,
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);
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}
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}
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