在Flutter中drawImage或paintImage均无法正常工作 [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在画布上。

  import'package：flutter /material.dart'作为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，出现了以下错误消息。

参数类型'Image（C：\ABC\flutter\packages\flutter\lib\src\widgets\image .dart）'不能分配给参数类型'Image（C：\ABC\flutter\bin\cache\pkg\sky_engine\lib\ui\painting.dart）'。

我真的不知道会出什么问题，我已经看到其他与ui.Image有着类似方法的代码。 / p>

请告知。

解决方案

有两个称为<$ c的类$ c>图像在不同包装中的变化。

有窗口小部件，其行为类似于窗口小部件，可以通过资产，内存或网络通过其命名的构造函数实例化。

还有ui包图片，该图片在较低级别（例如 CustomPainter 。由于此版本位于 ui 软件包中，因此通常使用 ui 前缀导入，如下所示：

  import'dart：ui'作为ui; 
  

不要将材料导入为 ui ！

要制作小部件，请使用 Image.asset 构造函数，并通过

要从资产中制作 ui.Image ，请使用以下代码段：

  Future< ui.Image> load（String asset）async {
 ByteData data = await rootBundle.load（asset）; 
 ui.Codec编解码器=等待ui.instantiateImageCodec（data.buffer.asUint8List（））; 
 ui.FrameInfo fi =等待codec.getNextFrame（）; 
返回图片。 
} 
  

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);

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

The argument type 'Image (C:\ABC\flutter\packages\flutter\lib\src\widgets\image.dart)' can't be assigned to the parameter type 'Image (C:\ABC\flutter\bin\cache\pkg\sky_engine\lib\ui\painting.dart)'.

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

Please advise.

解决方案

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

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.

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;

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

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

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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