How can I get the size of the Text Widget in flutter

Question

I've painted a shape for the background of my content of Text.

I want the background autoscale the Text, even the softWrap being true.

So, I need to get the width and height of my Text Widget before Widget build(BuildContext context).

Actually, I am simulating the chat bubble effect like iOS message using flutter. Here is the iOS version tutorial. Creating a Chat Bubble .

The core code below:

let label =  UILabel()
label.numberOfLines = 0
label.font = UIFont.systemFont(ofSize: 18)
label.textColor = .white
label.text = text

let constraintRect = CGSize(width: 0.66 * view.frame.width,
                            height: .greatestFiniteMagnitude)
let boundingBox = text.boundingRect(with: constraintRect,
                                    options: .usesLineFragmentOrigin,
                                    attributes: [.font: label.font],
                                    context: nil)
label.frame.size = CGSize(width: ceil(boundingBox.width),
                          height: ceil(boundingBox.height))

let bubbleSize = CGSize(width: label.frame.width + 28,
                             height: label.frame.height + 20)

let width = bubbleSize.width
let height = bubbleSize.height

=========================================
SOLUTION
Here is my solution.

bubble.dart:

// Define a CustomPainter to paint the bubble background.
class BubblePainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final Paint paint = Paint()
      ..color = Color(0xff188aff)
      ..style = PaintingStyle.fill;
    final Path bubble = Path()
      ..moveTo(size.width - 22.0, size.height)
      ..lineTo(17.0, size.height)
      ..cubicTo(
          7.61, size.height, 0.0, size.height - 7.61, 0.0, size.height - 17.0)
      ..lineTo(0.0, 17.0)
      ..cubicTo(0.0, 7.61, 7.61, 0.0, 17.0, 0.0)
      ..lineTo(size.width - 21, 0.0)
      ..cubicTo(size.width - 11.61, 0.0, size.width - 4.0, 7.61,
          size.width - 4.0, 17.0)
      ..lineTo(size.width - 4.0, size.height - 11.0)
      ..cubicTo(size.width - 4.0, size.height - 1.0, size.width, size.height,
          size.width, size.height)
      ..lineTo(size.width + 0.05, size.height - 0.01)
      ..cubicTo(size.width - 4.07, size.height + 0.43, size.width - 8.16,
          size.height - 1.06, size.width - 11.04, size.height - 4.04)
      ..cubicTo(size.width - 16.0, size.height, size.width - 19.0, size.height,
          size.width - 22.0, size.height)
      ..close();
    canvas.drawPath(bubble, paint);
  }

  @override
  bool shouldRepaint(BubblePainter oldPainter) => true;
}

// This is my custom RenderObject.
class BubbleMessage extends SingleChildRenderObjectWidget {
  BubbleMessage({
    Key key,
    this.painter,
    Widget child,
  }) : super(key: key, child: child);

  final CustomPainter painter;

  @override
  RenderCustomPaint createRenderObject(BuildContext context) {
    return RenderCustomPaint(
      painter: painter,
    );
  }

  @override
  void updateRenderObject(
      BuildContext context, RenderCustomPaint renderObject) {
    renderObject..painter = painter;
  }
}

Use the BubbleMessage Widget like this:

import 'bubble.dart' 

...code ... 

BubbleMessage(
  painter: BubblePainter(),
  child: Container(
    constraints: BoxConstraints(
      maxWidth: 250.0,
      minWidth: 50.0,
    ),
    padding: EdgeInsets.symmetric(horizontal: 15.0, vertical: 6.0),
    child: Text(
      'your text variable',
      softWrap: true,
      style: TextStyle(
        fontSize: 16.0,
      ),
    ),
  ),
),

...code ...

The bubble effect:

Answer 1

My apologies. This is not a direct answer on the topic's question! But If someone needs to get the size of a Text widget — this method can help. It helped me in creation of custom menu widget.

class TextSized extends StatelessWidget {
  const TextSized({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final String text = "Text in one line";
    final TextStyle textStyle = TextStyle(
      fontSize: 30,
      color: Colors.white,
    );
    final Size txtSize = _textSize(text, textStyle);

    // This kind of use - meaningless. It's just an example.
    return Container(
      color: Colors.blueGrey,
      width: txtSize.width,
      height: txtSize.height,
      child: Text(
        text,
        style: textStyle,
        softWrap: false,
        overflow: TextOverflow.clip,
        maxLines: 1,
      ),
    );
  }

  // Here it is!
  Size _textSize(String text, TextStyle style) {
    final TextPainter textPainter = TextPainter(
        text: TextSpan(text: text, style: style), maxLines: 1, textDirection: TextDirection.ltr)
      ..layout(minWidth: 0, maxWidth: double.infinity);
    return textPainter.size;
  }
}

Answer 2

Problem with other answers is that if you use Text widget to display your text and constraint it with measurements result without considering default font family and scale factor, then you will get wrong results because Text widget is using device's textScaleFactor by default and passing it to RichText widget inside of it. This is the correct code to measure text size:

final Size size = (TextPainter(
        text: TextSpan(text: text, style: textStyle),
        maxLines: 1,
        textScaleFactor: MediaQuery.of(context).textScaleFactor,
        textDirection: TextDirection.ltr)
      ..layout())
    .size;

Answer 3

I found another method without using the context:

final constraints = BoxConstraints(
  maxWidth: 800.0, // maxwidth calculated
  minHeight: 0.0,
  minWidth: 0.0,
);

RenderParagraph renderParagraph = RenderParagraph(
  TextSpan(
    text: text,
    style: TextStyle(
      fontSize: fontSize,
    ),
  ),
  textDirection: ui.TextDirection.ltr,
  maxLines: 1,
);
renderParagraph.layout(constraints);
double textlen = renderParagraph.getMinIntrinsicWidth(fontSize).ceilToDouble();