drawImage 或paintImage 在Flutter 中无法正常工作 [英] Either drawImage or paintImage doesn't work properly in Flutter

问题描述

我基本上想将资产文件夹中的图像显示到画布上.

I basically want to show an image that I have in the assets folder onto the canvas.

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

    ...

    ui.Image img = ui.Image.asset("images/some_image.png");
    ui.paintImage(canvas: canvas, image: img);

当我尝试将 img 分配给paintImage 的图像时收到以下错误消息.

And have got the following error message when I tried to assign img to paintImage's image.

参数类型 'Image (C:ABCflutterpackagesflutterlibsrcwidgetsimage.dart)' 不能分配给参数类型 'Image (C:ABCflutterincachepkgsky_enginelibuipainting.dart)'.

The argument type 'Image (C:ABCflutterpackagesflutterlibsrcwidgetsimage.dart)' can't be assigned to the parameter type 'Image (C:ABCflutterincachepkgsky_enginelibuipainting.dart)'.

我真的不知道会出什么问题，我见过其他代码与 ui.Image 有类似的方法.

I don't really know what could go wrong, I have seen other codes that had a similar approach with ui.Image.

请指教.

推荐答案

flutter 中有两个名为 Image 的类，在不同的包中.

There are two classes called Image in flutter, in different packages.

有 Widget，它的行为就像一个小部件，可以从资产、内存或网络通过其命名构造函数实例化.

There's the Widget, which behaves like a widget and can be instantiated from an asset, from memory or from the network through its named constructors.

还有 ui 包 Image 用于在较低级别绘制，例如在 CustomPainter 中.由于此版本在 ui 包中，因此通常使用 ui 前缀导入，如下所示:

There's also the ui package Image which is used when painting at a lower level, for example in a CustomPainter. Since this version is in the ui package it's normally imported with the ui prefix like this:

import 'dart:ui' as ui;

不要将material导入为ui！这会导致很多混乱.

Don't import material as ui! That will lead to a lot of confusion.

要制作小部件，请使用 Image.asset 构造函数，传递资产名称.

To make a widget, use the Image.asset constructor, passing the asset name.

要从资产制作ui.Image，请使用以下代码段:

To make a ui.Image from an asset use this snippet:

  Future<ui.Image> load(String asset) async {
    ByteData data = await rootBundle.load(asset);
    ui.Codec codec = await ui.instantiateImageCodec(data.buffer.asUint8List());
    ui.FrameInfo fi = await codec.getNextFrame();
    return fi.image;
  }

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