Flutter获取图片大小（网络图片和本地图片）

#使用 ##本地资源使用：

  AsperctRaioImage.asset(
            'images/img_home_bg.jpg',
            builder: (context, snapshot, url) {
              print('width=${snapshot.data.width}');
              print('heiht=${snapshot.data.height}');
              return Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text('本地资源加载',style: TextStyle(fontSize: 25.0,color: Colors.black),),
                  Text('大小--${snapshot.data.width.toDouble()}x${snapshot.data.height.toDouble()}',style: TextStyle(fontSize: 17.0),),
                  Container(
                    width: snapshot.data.width.toDouble() / 5,
                    height: snapshot.data.height.toDouble() / 5,
                    decoration: BoxDecoration(
                      image: DecorationImage(
                          image: AssetImage(url), fit: BoxFit.cover),
                    ),
                  )
                ],
              );
            },),

##网络资源使用：

AsperctRaioImage.network(
              'http://g.hiphotos.baidu.com/image/pic/item/c2cec3fdfc03924590b2a9b58d94a4c27d1e2500.jpg',
              builder: (context, snapshot, url) {
                return Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text('网络图片加载',style: TextStyle(fontSize: 25.0,color: Colors.black),),
                    Text('大小--${snapshot.data.width.toDouble()}x${snapshot.data.height.toDouble()}',style: TextStyle(fontSize: 17.0),),
                    Container(
                      width: snapshot.data.width.toDouble() / 5,
                      height: snapshot.data.height.toDouble() / 5,
                      decoration: BoxDecoration(
                        image: DecorationImage(
                            image: NetworkImage(url), fit: BoxFit.cover),
                      ),
                    )
                  ],
                );
              })

##AsperctRaioImage工具类

import 'dart:async';
import 'dart:io';
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'dart:ui' as ui;

typedef AsyncImageWidgetBuilder = Widget Function(
    BuildContext context, AsyncSnapshot snapshot, String url);

typedef AsyncImageFileWidgetBuilder = Widget Function(
    BuildContext context, AsyncSnapshot snapshot, File file);

typedef AsyncImageMemoryWidgetBuilder = Widget Function(
    BuildContext context, AsyncSnapshot snapshot, Uint8List bytes);

enum AsperctRaioImageType { NETWORK, FILE, ASSET, MEMORY }

///有宽高的Image
class AsperctRaioImage extends StatelessWidget {
  String url;
  File file;
  Uint8List bytes;
  final ImageProvider provider;
  AsperctRaioImageType type;
  AsyncImageWidgetBuilder builder;
  AsyncImageFileWidgetBuilder filebBuilder;
  AsyncImageMemoryWidgetBuilder memoryBuilder;

  AsperctRaioImage.network(url, {Key key, @required this.builder})
      : provider = NetworkImage(url),
        type = AsperctRaioImageType.NETWORK,
        this.url = url;

  AsperctRaioImage.file(
    file, {
    Key key,
    @required this.filebBuilder,
  })  : provider = FileImage(file),
        type = AsperctRaioImageType.FILE,
        this.file = file;

  AsperctRaioImage.asset(name, {Key key, @required this.builder})
      : provider = AssetImage(name),
        type = AsperctRaioImageType.ASSET,
        this.url = name;

  AsperctRaioImage.memory(bytes, {Key key, @required this.memoryBuilder})
      : provider = MemoryImage(bytes),
        type = AsperctRaioImageType.MEMORY,
        this.bytes = bytes;

  @override
  Widget build(BuildContext context) {
    final ImageConfiguration config = createLocalImageConfiguration(context);
    final Completer completer = Completer();
    final ImageStream stream = provider.resolve(config);
    ImageStreamListener listener;
    listener = ImageStreamListener(
          (ImageInfo image, bool sync) {
        completer.complete(image.image);
        stream.removeListener(listener);
      },
      onError: (dynamic exception, StackTrace stackTrace) {
        completer.complete();
        stream.removeListener(listener);
          FlutterError.reportError(FlutterErrorDetails(
            context: ErrorDescription('image failed to precache'),
            library: 'image resource service',
            exception: exception,
            stack: stackTrace,
            silent: true,
          ));
      },
    );
    stream.addListener(listener);

    return FutureBuilder(
        future: completer.future,
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.hasData) {
            if (type == AsperctRaioImageType.FILE) {
              return filebBuilder(context, snapshot, file);
            } else if (type == AsperctRaioImageType.MEMORY) {
              return memoryBuilder(context, snapshot, bytes);
            } else {
              return builder(context, snapshot, url);
            }
          } else {
            return Container();
          }
        });
  }
}