如何使用 flutter 在单击按钮时创建覆盖

Question

我想在单击按钮时打开覆盖面板，启用的覆盖 position 应该靠近单击操作发生的位置，如图所示

Answer 1

您可以使用 package https://pub.dev/packages/popup_menu
并修改此包的文件https://github.com/chinabrant/popup_menu/blob/master/lib/triangle_painter.dart将三角形左移 Z4757FE07FD492A360EA6A760DEZ6 代码如下

else {
      path.moveTo(size.width / 2.0 - 20, 0.0);
      path.lineTo(-20.0, size.height + 1);
      path.lineTo(size.width - 20 , size.height + 1);

代码片段

Container(
          color: Colors.blue,
          child: MaterialButton(
            height: 45.0,
            key: btnKey,
            onPressed: maxColumn,
            child: Text('Show Menu'),
          ),
        ),
...

void maxColumn() {
PopupMenu menu = PopupMenu(
    // backgroundColor: Colors.teal,
    // lineColor: Colors.tealAccent,
    maxColumn: 1,
    items: [
      MenuItem(title: 'Copy', image: Image.asset('assets/copy.png')),
    ],
    onClickMenu: onClickMenu,
    stateChanged: stateChanged,
    onDismiss: onDismiss);
menu.show(widgetKey: btnKey);
}

演示

完整的示例代码

import 'package:flutter/material.dart';
import 'package:popup_menu/popup_menu.dart';
import 'package:popup_menu_example/gesture_demo.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Popup Menu Example'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  PopupMenu menu;
  GlobalKey btnKey = GlobalKey();
  GlobalKey btnKey2 = GlobalKey();
  GlobalKey btnKey3 = GlobalKey();
  GlobalKey btnKey4 = GlobalKey();

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

    menu = PopupMenu(items: [
      // MenuItem(title: 'Copy', image: Image.asset('assets/copy.png')),
      // MenuItem(title: 'Home', image: Icon(Icons.home, color: Colors.white,)),
      MenuItem(
          title: 'Mail',
          image: Icon(
            Icons.mail,
            color: Colors.white,
          )),
      MenuItem(
          title: 'Power',
          image: Icon(
            Icons.power,
            color: Colors.white,
          )),
      MenuItem(
          title: 'Setting',
          image: Icon(
            Icons.settings,
            color: Colors.white,
          )),
      MenuItem(
          title: 'PopupMenu',
          image: Icon(
            Icons.menu,
            color: Colors.white,
          ))
    ], onClickMenu: onClickMenu, onDismiss: onDismiss, maxColumn: 4);
  }

  void stateChanged(bool isShow) {
    print('menu is ${isShow ? 'showing' : 'closed'}');
  }

  void onClickMenu(MenuItemProvider item) {
    print('Click menu -> ${item.menuTitle}');
  }

  void onDismiss() {
    print('Menu is dismiss');
  }

  @override
  Widget build(BuildContext context) {
    PopupMenu.context = context;

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        alignment: Alignment.centerRight,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.start,
          children: <Widget>[
            Container(
              color: Colors.blue,
              child: MaterialButton(
                height: 45.0,
                key: btnKey,
                onPressed: maxColumn,
                child: Text('Show Menu'),
              ),
            ),
            Container(
              child: MaterialButton(
                key: btnKey2,
                height: 45.0,
                onPressed: customBackground,
                child: Text('Show Menu'),
              ),
            ),
            Container(
              child: MaterialButton(
                key: btnKey3,
                height: 45.0,
                onPressed: onDismissOnlyBeCalledOnce,
                child: Text('Show Menu'),
              ),
            ),
            Container(
              child: MaterialButton(
                height: 30.0,
                child: Text('Gestures Demo'),
                onPressed: onGesturesDemo,
              ),
            ),
          ],
        ),
      ),
    );
  }

  void onDismissOnlyBeCalledOnce() {
    menu.show(widgetKey: btnKey3);
  }

  void onGesturesDemo() {
    menu.dismiss();
    return;
    Navigator.push(
      context,
      MaterialPageRoute(builder: (context) => GestureDemo()),
    );
  }

  void checkState(BuildContext context) {
    final snackBar = new SnackBar(content: new Text('这是一个SnackBar!'));

    Scaffold.of(context).showSnackBar(snackBar);
  }


  void maxColumn() {
    PopupMenu menu = PopupMenu(
        // backgroundColor: Colors.teal,
        // lineColor: Colors.tealAccent,
        maxColumn: 1,
        items: [
          MenuItem(title: 'Copy', image: Image.asset('assets/copy.png')),
        ],
        onClickMenu: onClickMenu,
        stateChanged: stateChanged,
        onDismiss: onDismiss);
    menu.show(widgetKey: btnKey);
  }

  //
  void customBackground() {
    PopupMenu menu = PopupMenu(
        // backgroundColor: Colors.teal,
        // lineColor: Colors.tealAccent,
        // maxColumn: 2,
        items: [
          MenuItem(title: 'Copy', image: Image.asset('assets/copy.png')),
          MenuItem(
              title: 'Home',
              // textStyle: TextStyle(fontSize: 10.0, color: Colors.tealAccent),
              image: Icon(
                Icons.home,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Mail',
              image: Icon(
                Icons.mail,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Power',
              image: Icon(
                Icons.power,
                color: Colors.white,
              )),
          MenuItem(
              title: 'Setting',
              image: Icon(
                Icons.settings,
                color: Colors.white,
              )),
          MenuItem(
              title: 'PopupMenu',
              image: Icon(
                Icons.menu,
                color: Colors.white,
              ))
        ],
        onClickMenu: onClickMenu,
        stateChanged: stateChanged,
        onDismiss: onDismiss);
    menu.show(widgetKey: btnKey2);
  }
}