Flutter：裁剪后图像内存无效图像数据答案

【问题标题】：Flutter: Image memory invalid image data after croppingFlutter：裁剪后图像内存无效图像数据
【发布时间】：2022-12-29 14:29:43
【问题描述】：

我正在使用 Flutter camera 包从相机拍摄照片，现在我正在尝试显示从拍摄的照片中裁剪的图像。我使用image包裁剪图片。正如您在以下代码中看到的，我调用了返回 img.Image 数据类型的 copyCrop 函数：

import 'package:image/image.dart' as img;

final XFile imageFile = await _controller.takePicture();
final bytes = await imageFile.readAsBytes();
final uncroppedImage = img.decodeImage(bytes);

final cropPosition = overlayKey.globalPaintBounds;

final img.Image croppedImage =
    img.copyCrop(
        uncroppedImage,
        cropPosition.left.toInt(),
        cropPosition.top.toInt(),
        cropPosition.width.toInt(),
        cropPosition.height.toInt());

我在将裁剪后的图像显示到 Flutter 中的图像小部件时遇到问题。如您所见，img.Image 数据类型与 Flutter 中的 Image 不同。然后我尝试将其转换为 Uint8List，然后使用 Image.memory 将其加载到小部件。

final croppedImageBytes = croppedImage.getBytes(); // return Uint8List

...
// somewhere else 

Image.memory(croppedImageBytes);

但是它给了我这样的错误：

E/FlutterJNI(20985): Failed to decode image
E/FlutterJNI(20985): android.graphics.ImageDecoder$DecodeException: Failed to create image decoder with message 'unimplemented'Input contained an error.
E/FlutterJNI(20985):    at android.graphics.ImageDecoder.nCreate(Native Method)
E/FlutterJNI(20985):    at android.graphics.ImageDecoder.access$200(ImageDecoder.java:173)
E/FlutterJNI(20985):    at android.graphics.ImageDecoder$ByteBufferSource.createImageDecoder(ImageDecoder.java:250)
E/FlutterJNI(20985):    at android.graphics.ImageDecoder.decodeBitmapImpl(ImageDecoder.java:1863)
E/FlutterJNI(20985):    at android.graphics.ImageDecoder.decodeBitmap(ImageDecoder.java:1856)
E/FlutterJNI(20985):    at io.flutter.embedding.engine.FlutterJNI.decodeImage(FlutterJNI.java:524)

======== Exception caught by image resource service ================================================
The following _Exception was thrown resolving an image codec:
Exception: Invalid image data

When the exception was thrown, this was the stack: 
#0      _futurize (dart:ui/painting.dart:5886:5)
#1      ImageDescriptor.encoded (dart:ui/painting.dart:5741:12)
#2      instantiateImageCodecFromBuffer (dart:ui/painting.dart:2092:60)
#3      PaintingBinding.instantiateImageCodecFromBuffer (package:flutter/src/painting/binding.dart:153:15)
#4      MemoryImage._loadAsync (package:flutter/src/painting/image_provider.dart:1090:20)
<asynchronous suspension>
====================================================================================================

但是，每当我直接使用 Uint8List 加载图像（不裁剪）时，它仍然可以正常工作。有什么解决方案可以解决这个问题吗？

【问题讨论】：

标签： flutter base64 byte image-flutter

【解决方案1】：

我终于找到了解决这个问题的方法。我只需要先对字节进行编码，然后再将其加载到 Image.memory（来自 Flutter）中。这是SN-P。

bytes = Uint8List.fromList(img.encodePng(croppedImage));

// somewhere in your widget

Image.memory(bytes);

【讨论】：