When CircularProgressIndicator's value is null, it paints nothing instead of displaying a loading spinner

[paolosoares]

Running this app:

runApp(
  new MaterialApp(
    home: new Scaffold(
      body: new Center(
        child: new CircularProgressIndicator(),
      ),
    ),
  ),
);

I expected to see a circular spinner on the center of the screen, since CircularProgressIndicator's documentation says:

Indeterminate. Indeterminate progress indicators do not have a specific value at each point in time and instead indicate that progress is being made without indicating how much progress remains. To create an indeterminate progress indicator, use a null value.

However, all I see is a blank screen.

Looking at _CircularProgressIndicatorPainter, I see that it doesn't do any special handling for "value == null" besides changing the stroke cap, possibly to not paint a dot:

@override
void paint(Canvas canvas, Size size) {
  final Paint paint = new Paint()
    ..color = valueColor
    ..strokeWidth = strokeWidth
    ..style = PaintingStyle.stroke;

  if (value == null) // Indeterminate
    paint.strokeCap = StrokeCap.square;

  canvas.drawArc(Offset.zero & size, arcStart, arcSweep, false, paint);
}

[paolosoares]

Actually, I've just found out that it behaves just fine on other clients. I'm trying to track down what's different on my setup.

[tvolkert]

We use a null value in the gallery, and it correctly spins:

flutter/examples/flutter_gallery/lib/demo/material/progress_indicator_demo.dart

Line 76 in d996ab9

const CircularProgressIndicator(),

Could it be that no animations are running in your case? Maybe you need a vsync?

@HansMuller

[paolosoares]

Found it: I didn't enable OpenGL when starting the emulator.

[github-actions]

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