105 lines
3.8 KiB
Dart
105 lines
3.8 KiB
Dart
import 'dart:async';
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import 'dart:ui' as ui;
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import 'package:flutter/foundation.dart';
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import 'package:flutter/painting.dart';
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import 'package:flutter_map/flutter_map.dart';
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import 'package:http/http.dart' as http;
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/// ESRI World Imagery 底图地址（国内网络可能不可达）
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const String kEsriWorldImageryUrl =
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'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/{z}/{y}/{x}';
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/// 网络超时时长（瓦片加载）
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const Duration _kTileTimeout = Duration(seconds: 8);
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/// ─────────────────────────────────────────────────────────
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/// 容错网络瓦片图
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/// ─────────────────────────────────────────────────────────
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///
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/// 加载失败（超时 / 断网 / 404 等）时返回 1×1 透明 PNG，
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/// 避免 SocketException 刷屏并保证地图其余部分正常渲染。
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class ResilientNetworkImage extends ImageProvider<ResilientNetworkImage> {
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const ResilientNetworkImage(this.url);
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final String url;
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@override
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Future<ResilientNetworkImage> obtainKey(ImageConfiguration configuration) =>
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SynchronousFuture<ResilientNetworkImage>(this);
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@override
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ImageStreamCompleter loadImage(
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ResilientNetworkImage key,
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ImageDecoderCallback decode,
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) {
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return MultiFrameImageStreamCompleter(
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codec: _loadAsync(decode),
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scale: 1.0,
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debugLabel: 'ResilientNetworkImage(${url.split('/').last})',
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);
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}
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Future<ui.Codec> _loadAsync(ImageDecoderCallback decode) async {
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try {
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final client = http.Client();
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final response = await client
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.get(Uri.parse(url))
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.timeout(_kTileTimeout);
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if (response.statusCode == 200 && response.bodyBytes.isNotEmpty) {
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final buffer = await ui.ImmutableBuffer.fromUint8List(
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response.bodyBytes,
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);
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return decode(buffer);
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}
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} catch (_) {
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// 超时 / 网络异常 / 解码失败 → 走下面的透明兜底
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}
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// 1×1 透明 PNG，避免 Flutter 框架抛出 MissingImageException
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return decode(
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await ui.ImmutableBuffer.fromUint8List(_transparentPng),
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);
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}
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@override
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bool operator ==(Object other) =>
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other is ResilientNetworkImage && other.url == url;
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@override
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int get hashCode => url.hashCode;
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}
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/// ─────────────────────────────────────────────────────────
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/// 容错 TileProvider —— 直接在 TileLayer.tileProvider 中使用
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/// ─────────────────────────────────────────────────────────
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///
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/// ```dart
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/// TileLayer(
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/// urlTemplate: kEsriWorldImageryUrl,
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/// tileProvider: ResilientTileProvider(),
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/// minZoom: 0,
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/// maxZoom: 19,
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/// )
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/// ```
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class ResilientTileProvider extends TileProvider {
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@override
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ImageProvider<Object> getImage(TileCoordinates coordinates, TileLayer options) {
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final url = getTileUrl(coordinates, options);
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return ResilientNetworkImage(url);
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}
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}
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/// 1×1 透明 PNG 字节（兜底用）
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final Uint8List _transparentPng = Uint8List.fromList(<int>[
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0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A, // PNG signature
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0x00, 0x00, 0x00, 0x0D, 0x49, 0x48, 0x44, 0x52, // IHDR chunk
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0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, // 1×1
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0x08, 0x06, 0x00, 0x00, 0x00, 0x1F, 0x15, 0xC4, // RGBA 8bit
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0x89, 0x00, 0x00, 0x00, 0x0A, 0x49, 0x44, 0x41, // IDAT chunk
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0x54, 0x78, 0x9C, 0x62, 0x00, 0x00, 0x00, 0x02,
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0x00, 0x01, 0xE5, 0x27, 0xDE, 0xFC, 0x00, 0x00, // compressed data
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0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, // IEND chunk
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0x60, 0x82,
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]);
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