Stack() Widget not centering all sub widgets flutter

Question

I have a Text() widget I am trying to stack on a CircularProgressIndicator()

I thought it would be as simple as just wrapping them both in a Stack() widget but the text is not centered.

I tried wrapping the Text() in a Center() widget but that did not solve the issue:

                    return Expanded(
                      child: PageView(
                        controller: pageViewController,
                        children: [
                          PackSummaryWeightGraph(
                              categoryWeightList: categoryWeightList,
                              totalWeight: totalWeight),
                          Column(
                            mainAxisAlignment: MainAxisAlignment.center,
                            children: [
                              Center(
                                child: Stack(
                                  children: [
                                    Text((packedItemsPercent * 100)
                                        .toString()),
                                    SizedBox(
                                      height: 150,
                                      width: 150,
                                      child: CircularProgressIndicator(
                                        value: packedItemsPercent,
                                      ),
                                    ),
                                  ],
                                ),
                              ),
                            ],
                          ),
                          const Center(
                            child: Text('Third Page'),
                          ),
                        ],
                      ),
                    );

Bonus points if there is a way to have the CircularProgressIndicator() fill the space without hard coding its width and height...

Answer 1

Stack has an alignment argument:

Stack(
  alignment: Alignment.center, 
  children: [...],
),

If you want to fill the given space use the SizedBox.expand constructor:

SizedBox.expand(
  child: CircularProgressIndicator(
    value: packedItemsPercent,
  ),
),

One issue with the above is that if the available space has a different height than width you will end up with an oval shaped indicator rather than a circle. You can avoid this by wrapping it in an AspectRatio widget:

AspectRatio(
  aspectRatio: 1,
  child: SizedBox.expand(
    child: CircularProgressIndicator(
      value: packedItemsPercent,
    ),
  ),
),

See complete demo:

import 'package:flutter/material.dart';

void main() {
  double packedItemsPercent = .67;

  runApp(
    MaterialApp(
      home: Scaffold(
        body: Stack(
          alignment: Alignment.center,
          children: [
            Text((packedItemsPercent * 100).toString()),
            AspectRatio(
              aspectRatio: 1,
              child: SizedBox.expand(
                child: CircularProgressIndicator(
                  value: packedItemsPercent,
                ),
              ),
            ),
          ],
        ),
      ),
    ),
  );
}

Make sure that any widget like Expanded or SizedBox.expand is not inside of an infinite sized container like a ListView or similar. Expanded means to take up the maximum available space, but that isn't possible if you have an infinite amount of space.

Answer 2

You'll need to set the alignment of the Stack to center:

Stack(
  alignment: Alignment.center,
  children: [
    // ...
  ],
);

To get the circular progress indicator to fill the space, you should be able to use a FittedBox with a Positioned.fill widget:

Stack(
  children: [
    Positioned.fill(
      child: FittedBox(
        fit: BoxFit.fill,
        child: CircularProgressIndicator(
          value: packedItemsPercent
        ),
      ),
    ),
  ],
);