Flutter 的 TextPainter 抛出一个 '!_needsLayout': is not true.'例外

Question

我尝试使用 TextPainter 来获取 Text Widget 中字符串的最大长度，但是如果我调用 painter，它会抛出 !_needsLayout': is not true. 异常。

异常

The following assertion was thrown building FeedPage(dirty, dependencies: [MediaQuery], state: _FeedPageState#9c489):
'package:flutter/src/painting/text_painter.dart': Failed assertion: line 546 pos 12: '!_needsLayout': is not true.

使用 TextPainter 的方法

int maxCharCountToFit(String content) {
    List<String> splitted = content.split(" ");

    for (int i = splitted.length; i >= 0; i--) {
      bool retry = TextPainter(
            text: TextSpan(text: splitted.sublist(0, splitted.length - i).join(" "), style: pageTextStyle),
            maxLines: 25,
            textScaleFactor: MediaQuery.of(context).textScaleFactor,
            textDirection: TextDirection.ltr,
          ).didExceedMaxLines ==
          false;

      if (retry == false) {
        return splitted.sublist(0, i).length;
      }
    }

    return 0;
  }

完整文件

请see this file on GitHub.

Answer 1

在调用 layout 之前，不会计算绘制文本的大小。这必须在访问任何与大小相关的属性之前完成，例如 didExceedMaxLines.

有关详细信息，请参阅 API documentation。

Flutter 的 TextPainter 抛出一个 '!_needsLayout': is not true.'例外

Flutter's TextPainter throws an '!_needsLayout': is not true.' exception

android

dart

flutter

flutter-android