flutter开发实战-自定义长按TextField输入框剪切、复制、选择全部菜单AdaptiveTextSelectionToolba样式UI效果

在Flutter中，可以通过TextField的toolbarOptions属性来实现长按时弹出的系统菜单。但是，Flutter 目前不支持自定义这些系统菜单。因此，如果你想实现自定义的剪切、拷贝、选择全部等菜单项，你需要使用TextField的onTap回调来自己处理长按事件，并显示自定义的菜单。

以下是一个简单的示例，展示如何实现自定义的长按菜单：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
 
void main() {
  runApp(MyApp());
}
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: AdaptiveTextField(),
        ),
      ),
    );
  }
}
 
class AdaptiveTextField extends StatefulWidget {
  @override
  _AdaptiveTextFieldState createState() => _AdaptiveTextFieldState();
}
 
class _AdaptiveTextFieldState extends State<AdaptiveTextField> {
  TextEditingController _controller = TextEditingController();
 
  @override
  Widget build(BuildContext context) {
    return TextField(
      controller: _controller,
      onTap: () {
        showMenu(context: context, position: RelativeRect.fromLTRB(20, 20, 20, 20));
      },
    );
  }
 
  void showMenu({required BuildContext context, required RelativeRect position}) {
    final RenderBox renderBox = context.findRenderObject()! as RenderBox;
    final TextSelectionControls controls = MaterialTextSelectionControls();
    final Matrix4 transform = renderBox.getTransformTo(null);
    final Offset textFieldPos = transform.getTranslation();
    final Rect textFieldRect = RelativeRect.fromLTRB(
      textFieldPos.dx,
      textFieldPos.dy,
      textFieldPos.dx + renderBox.size.width,
      textFieldPos.dy + renderBox.size.height,
    ).toRect(context.screen.size);
 
    controls.getToolbar(
      context,
      _controller,
      textFieldRect,
      position,
    ).then((ToolbarOptions? options) {
      if (options != null) {
        showMenu<void>(
          context: context,
          items: <PopupMenuEntry<String>>[
            const PopupMenuItem<String>(
              value: '复制',
              child: Text('复制'),
            ),
            const PopupMenuItem<String>(
              value: '剪切',
              child: Text('剪切'),
            ),
            const PopupMenuItem<String>(
              value: '选择全部',
              child: Text('选择全部'),
            ),
          ],
        ).then((String? value) {
          if (v