无法无条件访问属性“窗口”，因为接收者可以为“空”

Question

将其连接到 Firebase 后，此错误出现在我的颤振应用程序上。 不确定这是否与错误的原因有关。 这是代码

Size size = WidgetsBinding.instance.window.physicalSize /
    WidgetsBinding.instance.window.devicePixelRatio;

///This method is used to set padding/margin (for the left and Right side) & width of the screen or widget according to the Viewport width.
double getHorizontalSize(double px) {
  return px * (size.width / 360);
}

///This method is used to set padding/margin (for the top and bottom side) & height of the screen or widget according to the Viewport height.
double getVerticalSize(double px) {
  num statusBar = MediaQueryData.fromWindow(WidgetsBinding.instance.window)
      .viewPadding
      .top;
  num screenHeight = size.height - statusBar;
  return px * (screenHeight / 800);
}

///This method is used to set text font size according to Viewport
double getFontSize(double px) {
  var height = getVerticalSize(px);
  var width = getHorizontalSize(px);
  if (height < width) {
    return height.toInt().toDouble();
  } else {
    return width.toInt().toDouble();
  }
}

///This method is used to set smallest px in image height and width
double getSize(double px) {
  var height = getVerticalSize(px);
  var width = getHorizontalSize(px);
  if (height < width) {
    return height.toInt().toDouble();
  } else {
    return width.toInt().toDouble();
  }
}``` 

Answer 1

如果您还没有使用 Flutter 3，则 WidgetsBinding.instance 为nullable 。

这意味着您必须使用WidgetsBinding.instance!.window或WidgetsBinding.instance?.window 。

您还可以在main()方法中调用WidgetsBinding.ensureInitialized()以确保 WidgetsBinding 的实例存在。