Flutter - 如何在 TextField 中获取光标的坐标？

Question

需要知道TextField中当前光标位置的dx和dy坐标。这是实现提及/标签功能所必需的，其中需要在 TextField 的光标下方几个像素处显示一个弹出窗口。

Answer 1

您可以使用FocusNode 来获取文本字段本身的偏移量。然后使用TextPainter 类计算布局宽度，如post 所示，并使用它来定位您的标签。然后也许使用一些覆盖逻辑来显示标签，如here所示。

1. 创建一个FocusNode 对象并将其附加到文本字段。
2. 然后在onChanged 回调或其TextEditingController 的回调中继续使用FocusNode.offset.dx 和FocusNode.offset.dy 定位您的标签的逻辑。
3. FocusNode 仅提供边界矩形偏移。所以你需要一个TextPainter 实例来计算新输入文本的宽度。为此，您需要提前定义 TextStyle。
4. 同时使用 2 和 3 中的值来计算标签的位置，并为视觉美学增加一些额外的偏移量。

以下代码是使用上述技术的示例。此解决方案的实时版本可在此dartpad 中获得。

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter  Show Text Tag Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Show Text Tag demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  FocusNode _focusNode = FocusNode();
  GlobalKey _textFieldKey = GlobalKey();
  TextStyle _textFieldStyle = TextStyle(fontSize: 20);

  @override
  void initState() {
    super.initState();
  }

  // Code reference for overlay logic from MTECHVIRAL's video
  // https://www.youtube.com/watch?v=KuXKwjv2gTY

  showOverlaidTag(BuildContext context, String newText) async {

    TextPainter painter = TextPainter(
      textDirection: TextDirection.ltr,
      text: TextSpan(
        style: _textFieldStyle,
        text: newText,
      ),
    );
    painter.layout();


    OverlayState overlayState = Overlay.of(context);
    OverlayEntry suggestionTagoverlayEntry = OverlayEntry(builder: (context) {
      return Positioned(

        // Decides where to place the tag on the screen.
        top: _focusNode.offset.dy + painter.height + 3,
        left: _focusNode.offset.dx + painter.width + 10,

        // Tag code.
        child: Material(
            elevation: 4.0,
            color: Colors.lightBlueAccent,          
            child: Text(
              'Show tag here',
              style: TextStyle(
                fontSize: 20.0,
              ),
            )),
      );
    });
    overlayState.insert(suggestionTagoverlayEntry);

    // Removes the over lay entry from the Overly after 500 milliseconds 
    await Future.delayed(Duration(milliseconds: 500));
    suggestionTagoverlayEntry.remove();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          child: TextField(
            focusNode: _focusNode,
            key: _textFieldKey,
            style: _textFieldStyle,
            onChanged: (String nextText) {
              showOverlaidTag(context, nextText);
            },
          ),
          width: 400.0,
        ),
      ),
    );
  }
}

如下所示的屏幕截图。您必须调整位置以满足您的需要，如果您要使用它，还必须调整叠加层的持续时间/可见性逻辑。

Answer 2

要获取当前光标的坐标（也称为caret）在颤振的文本字段中，我认为您可以使用返回TextPainter > getOffsetForCaret方法>offset 绘制插入符号的位置。然后，从偏移量你可以得到插入符号的 x 和 y 组件。

观察下面代码中的xCarret、yCarret，它们对应屏幕上光标的左上角坐标。 您可以通过将preferredLineHeight 添加到yCarret 来推断yCarretBottom 的位置。

方法getOffsetForCaret需要一个caretPrototype，我们用Rect.fromLTWH和TextField的属性cursorWidth给出的光标宽度。

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Get cursor (caret) position',
      debugShowCheckedModeBanner: false,
      home: MyHomePage(title: 'Get cursor (caret) position'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, this.title}) : super(key: key);

  final String? title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  GlobalKey _textFieldKey = GlobalKey();
  TextStyle _textFieldStyle = TextStyle(fontSize: 20);
  TextEditingController _textFieldController = TextEditingController();
  late TextField _textField;
  double xCaret = 0.0;
  double yCaret = 0.0;
  double painterWidth = 0.0;
  double painterHeight = 0.0;
  double preferredLineHeight = 0.0;

  @override
  void initState() {
    super.initState();

    /// Listen changes on your text field controller
    _textFieldController.addListener(() {
      _updateCaretOffset(_textFieldController.text);
    });
  }

  void _updateCaretOffset(String text) {
    TextPainter painter = TextPainter(
      textDirection: TextDirection.ltr,
      text: TextSpan(
        style: _textFieldStyle,
        text: text,
      ),
    );
    painter.layout();

    TextPosition cursorTextPosition = _textFieldController.selection.base;
    Rect caretPrototype = Rect.fromLTWH(
        0.0, 0.0, _textField.cursorWidth, _textField.cursorHeight ?? 0);
    Offset caretOffset =
        painter.getOffsetForCaret(cursorTextPosition, caretPrototype);
    setState(() {
      xCaret = caretOffset.dx;
      yCaret = caretOffset.dy;
      painterWidth = painter.width;
      painterHeight = painter.height;
      preferredLineHeight = painter.preferredLineHeight;
    });
  }

  @override
  Widget build(BuildContext context) {
    String text = '''
xCaret: $xCaret
yCaret: $yCaret
yCaretBottom: ${yCaret + preferredLineHeight}
''';

    _textField = TextField(
      controller: _textFieldController,
      keyboardType: TextInputType.multiline,
      key: _textFieldKey,
      style: _textFieldStyle,
      minLines: 1,
      maxLines: 2,
    );

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title!),
      ),
      body: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            Text(text),
            Padding(
              child: _textField,
              padding: EdgeInsets.all(40),
            ),
          ]),
    );
  }
}

Answer 3

获取输入字段光标或插入符号当前位置的简单方法

TextField(
  controller: _textController,
  onChanged: (value) {
    int cursorPos = _textController.selection.base.offset;
    print(cursorPos); // returns value current position where you just typed
  }
)