Image为null，Uint8List-Flutter

Question

我正在尝试将图像编码为Uint8List，但它为我提供了空值

  List<int> bytes;
  I.Image _img;

  @override
  void initState() {
    super.initState();
    WidgetsFlutterBinding.ensureInitialized();
    String file = 'lib/graphics/logo.png';
    readFileAsync(file);
  }

  Future<dynamic> readFileAsync(String filePath) async {
    var imageData = await rootBundle.load('lib/graphics/logo.png');
    bytes = Uint8List.view(imageData.buffer);
    _img = I.decodeImage(bytes);
  }

并从小部件树中调用它

Container(
  child: Image.memory(_img.getBytes()),
),

错误

I/flutter (26125): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (26125): The following NoSuchMethodError was thrown building LayoutBuilder:
I/flutter (26125): The method 'getBytes' was called on null.
I/flutter (26125): Receiver: null
I/flutter (26125): Tried calling: getBytes()

Answer 1

您会得到一个空值，因为load方法是一个Future，而您不必在构建方法上等待它。

您必须检查_img是否为空，如果是，则显示另一个小部件，例如Text或CircularProgressIndicator：

Container(
  child: _img ? Image.memory(_img.getBytes()) : Text('loading...'),
), 

之后，您需要调用setState()方法以在readFileAsync方法中重建窗口小部件：

setState() {
  _img = I.decodeImage(bytes);
}