Flutter 获取系统相册

iOS需要再项目内配置plist文件，申请访问权

NSPhotoLibraryUsageDescription
Example usage description
NSCameraUsageDescription
Example usage description

在pubspec.yaml中添加依赖：

  image_picker: ^0.6.0+4

Future getImage() async {
    var image = await ImagePicker.pickImage(source: ImageSource.gallery);

    setState(() {
      if (image != null) _image = image;
    });
  }