[英]How to create subclass from abstract class ui,Image in Dart / Flutter?
我正在嘗試將本地資產圖像加載到ui.Image對象中。 但是ui.Image是一個抽象類。 我基本上有這個:
import 'dart:ui' as ui;
class MyImage implements ui.Image{
int height;
int width;
MyImage(String file){
}
@override
void dispose() {
// TODO: implement dispose
super.dispose();
}
@override
String toString() {
// TODO: implement toString
return super.toString();
}
}
將代碼與下面的函數定義一起使用。 錯誤在'ui.Image image = await loadImage(img); 'await用紅色下划線標出,工具提示為'函數體中未定義名稱'await',未標記異步。'
class TrialApp extends StatefulWidget {
@override
_TrialAppState createState() => new _TrialAppState();
}
class _TrialAppState extends State<TrialApp> {
NodeWithSize rootNode;
@override
void initState() {
// TODO: implement initState
super.initState();
rootNode = new NodeWithSize(new Size(400.0, 400.0));
}
@override
Widget build(BuildContext context) {
// define a function that converts the I.Image object into ui.Image
//object
Future<ui.Image> loadImage(I.Image img) async {
final Completer<ui.Image> imageCompleter = new Completer();
ui.decodeImageFromList(img.getBytes(), (ui.Image img) {
imageCompleter.complete(img);
});
return imageCompleter.future;
}
// Obtain a `I.Image` object from the image file
I.Image img = I.decodeImage(new io.File('images/tile.png').readAsBytesSync());
// Obtain the `ui.Image` from the `I.Image` object
ui.Image image = await loadImage(img);
Sprite myButton = new Sprite.fromImage(image);
rootNode.addChild(myButton);
return new SpriteWidget(rootNode);
}
}
首先使用rootBundle
從assetbundle獲取圖像。 將獲得的ByteData
轉換為List<int>
。 現在,你可以得到一個ui.Image
使用decodeImageFromList
方法。
例:
// import statements
import 'dart:async';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:spritewidget/spritewidget.dart';
class TrialApp extends StatefulWidget {
@override
_TrialAppState createState() => new _TrialAppState();
}
class _TrialAppState extends State<TrialApp> {
NodeWithSize rootNode = new NodeWithSize(new Size(400.0, 400.0));
@override
void initState() {
super.initState();
init();
}
Future<Null> init() async {
rootNode = new NodeWithSize(new Size(400.0, 400.0));
// Read file from assetbundle
final ByteData data = await rootBundle.load('images/tile.png');
// Convert the obtained ByteData into ui.Image
final ui.Image image = await loadImage(new Uint8List.view(data.buffer)); // Uint8List converts the ByteData into List<int>
Sprite myButton = new Sprite.fromImage(image);
rootNode.addChild(myButton);
// notify to redraw with child
setState(() {
rootNode = rootNode;
});
}
// define a function that converts the List<int> into ui.Image object
Future<ui.Image> loadImage(List<int> img) async {
final Completer<ui.Image> imageCompleter = new Completer();
ui.decodeImageFromList(img, (ui.Image img) {
imageCompleter.complete(img);
});
return imageCompleter.future;
}
@override
Widget build(BuildContext context) {
return new Container(
color: Colors.white,
child: new SpriteWidget(rootNode),
);
}
}
希望有幫助!
如果使用SpriteWidget,則可以使用ImageMap
類加載圖像以保存一些代碼。 從SpriteWidget文檔中:
ImageMap images = new ImageMap(rootBundle);
// Load a single image
ui.Image image = await images.loadImage('assets/my_image.png');
// Load multiple images
await images.load(<String>[
'assets/image_0.png',
'assets/image_1.png',
'assets/image_2.png',
]);
// Access a loaded image from the ImageMap
image = images['assets/image_0.png'];
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