How do I programmatically simulate onTap on a button in Flutter?

For example:

// Update: This GestureDetector is embedded inside a third party package
// that will invoke a series of animation along with the onTap button
GestureDetector(
   onTap: () => print('Hey There!'),
   child: Widget1(),
)


// Then another place in the same screen
GestureDetector(
    onDoubleTap: () { 
           //Call the onTap of Widget1's GestureDetector
           print('I'm Here');
        }
    child: Widget2(),
)

What I wanted is when a user double tap Widget2, it will also invoke the onTap call back of Widget1.

Update: So I do not want to just invoke a function passed into the onTap of GestureDetector of Widget1, but rather to programmatically tap the onTap of Widget1's GestureDetector

How do I do that?

You can do something like this -

Create your gesture detector -

   GestureDetector gestureDetector = GestureDetector(
      onTap: () {
        setState(() {
          _lights = !_lights;
        });
      },
      child: Container(
        color: Colors.yellow.shade600,
        padding: const EdgeInsets.all(8),
        child: const Text('TURN LIGHTS ON'),
      ),
    );

Create a button (or any widgetthat you would like to use) to call onTap on GestureDetector gestureDetector.onTap() just like you call method on another widget. (I am using a FlatButton here)-

          FlatButton(
            color: Colors.blue,
            textColor: Colors.white,
            disabledColor: Colors.grey,
            disabledTextColor: Colors.black,
            padding: EdgeInsets.all(8.0),
            onPressed: () {
              //Trigger the GestureDetector onTap event.
              gestureDetector.onTap();
            },
            child: Text("Click Here"),
          ),

Now you can click on the FlatButton to call the onTap event on GestureDetector.

Here is the complete example -

import 'package:flutter/material.dart';

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

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

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  bool _lights = false;

  @override
  Widget build(BuildContext context) {
    GestureDetector gestureDetector = GestureDetector(
      onTap: () {
        setState(() {
          _lights = !_lights;
        });
      },
      child: Container(
        color: Colors.yellow.shade600,
        padding: const EdgeInsets.all(8),
        child: const Text('TURN LIGHTS ON'),
      ),
    );

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          alignment: FractionalOffset.center,
          color: Colors.white,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Icon(
                  Icons.lightbulb_outline,
                  color: _lights ? Colors.yellow.shade600 : Colors.black,
                  size: 60,
                ),
              ),
              gestureDetector,
              SizedBox(height: 50.0),
              FlatButton(
                color: Colors.blue,
                textColor: Colors.white,
                disabledColor: Colors.grey,
                disabledTextColor: Colors.black,
                padding: EdgeInsets.all(8.0),
                onPressed: () {
                  gestureDetector.onTap();
                },
                child: Text("Click Here"),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

You will get something like this -