Get the length of a string inside a text at the point where it overflows-CodePudding

I have a long String inside a Text Widget. I have placed the widget inside a SizedBox widget with some fixed width, and I have given the Text Widget a maxLines of 4. Is there a way to get the length of the displayed string? I.e., I want to get the number of characters that were displayed on the screen, before TextOverflow was used.

CodePudding user response：

Looping is expensive, and hopefully you can find another way.

  test() {
    var str = '''
    Flutter transforms the app development process. Build, test, 
    and deploy beautiful mobile, web, desktop, and embedded apps
    from a single codebase.''';

    print(hasTextOverflow(str, TextStyle(fontSize: 14), 100, 300, 4)); // true
  }

  bool hasTextOverflow(String text, TextStyle style, double minWidth,
      double maxWidth, int maxLines) {
    final TextPainter textPainter = TextPainter(
      text: TextSpan(text: text, style: style),
      maxLines: maxLines,
      textDirection: TextDirection.ltr,
    )..layout(minWidth: minWidth, maxWidth: maxWidth);
    return textPainter.didExceedMaxLines;
  }

CodePudding user response：

You can use the TextPainter for this, it allows you to get paint separately a text, and it is responsible for painting the Text widget :

      // This is the text we are testing with
      String text = 'Text Example';
      
      // This is the width of the SizedBox/Container
      double width = 30;
      
      // maxLines of widget
      int maxLines = 2;

      // and here is the TextPainter declaration
      TextPainter textPainterExample = TextPainter(
        text: TextSpan(
          text: text,
        ),
        textDirection: TextDirection.ltr,
        maxLines: maxLines,
      );
      
      // we simulate the painting of that text and get registered information about it such as offsets...
      textPainterExample.layout(maxWidth: width);
    
      // and this is the index of the letter which starts overflowing on
      final indexOfOverflowing = textPainterExample.getPositionForOffset(Offset(width, 0)).offset;

and now that you got that indexOfOverflowing where the text starts overflowing, you can simply substring it like this:

String limitedText = text.substring(0, indexOfOverflowing);

and you can use now the limitedText.