calculatePositionOffset function

Offset calculatePositionOffset({ required BuildContext context, required Alignment alignment, })

Calculates the positional offset that the dialog should take relative to the BuildContext associated with the widget that opened it. For example, if the specified alignment is Alignment.bottomRight, then since the position of the dialog starts at the top-left relative to the widget that opened it, the dialog can be positioned at the bottom right of that box using a positional offset of: x-axis: renderBoxOffset.dx + renderBoxWidth y-axis: renderBoxOffset.dy + renderBoxHeight The translational offset function below is then used to translate the dialog relative to its own width, since its coordinates also start top-left and to achieve a Alignment.bottomRight alignment, it needs to be translated in the x-axis by its own width to align its right bound with the right bound of the widget that opened it and in the y-axis by its own height to also align its bottom bound with the bottom of the widget that opened it.

Implementation

Offset calculatePositionOffset({
  required BuildContext context,
  required Alignment alignment,
}) {
  // The insets for parts of the display that are completely obscured by system UI,
  /// typically by the device's keyboard.
  final viewInsets = MediaQuery.of(context).viewInsets;
  // The padding for parts of the display that are partially obscured by system UI like device notches.
  final devicePadding = MediaQuery.of(context).padding;
  final bottomPadding = max(viewInsets.bottom, devicePadding.bottom);
  final topPadding = devicePadding.top;
  final verticalPadding = (topPadding - bottomPadding).abs();

  // This is the render box of the widget that the dialog should be positioned relative to.
  final RenderBox renderBox = context.findRenderObject() as RenderBox;
  final renderBoxSize = renderBox.size;
  final renderBoxHeight = renderBoxSize.height;
  final renderBoxWidth = renderBoxSize.width;

  final renderBoxOffset = renderBox.localToGlobal(
    Offset.zero,
  );

  if (alignment == Alignment.bottomLeft) {
    return Offset(
      renderBoxOffset.dx,
      renderBoxOffset.dy + renderBoxHeight - bottomPadding,
    );
  } else if (alignment == Alignment.bottomCenter) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth / 2,
      renderBoxOffset.dy + renderBoxHeight - bottomPadding,
    );
  } else if (alignment == Alignment.bottomRight) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth,
      renderBoxOffset.dy + renderBoxHeight - bottomPadding,
    );
  } else if (alignment == Alignment.centerLeft) {
    return Offset(
      renderBoxOffset.dx,
      renderBoxOffset.dy + (renderBoxHeight - verticalPadding) / 2,
    );
  } else if (alignment == Alignment.center) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth / 2,
      renderBoxOffset.dy + (renderBoxHeight - verticalPadding) / 2,
    );
  } else if (alignment == Alignment.centerRight) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth,
      renderBoxOffset.dy + (renderBoxHeight - verticalPadding) / 2,
    );
  } else if (alignment == Alignment.topLeft) {
    return Offset(
      renderBoxOffset.dx,
      renderBoxOffset.dy + topPadding,
    );
  } else if (alignment == Alignment.topCenter) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth / 2,
      renderBoxOffset.dy + topPadding,
    );
  } else if (alignment == Alignment.topRight) {
    return Offset(
      renderBoxOffset.dx + renderBoxWidth,
      renderBoxOffset.dy + topPadding,
    );
  }

  throw ('Unsupported alignment');
}