How do I add both onPressed and onLongPress to a Flutter Center Widget inside a Row?

Question

I am trying in vain to add onLongPress to an image button along with onPressed. I get error: The named parameter 'onDoubleTap' isn't defined.

I have multiple rows of 2 horizontal image buttons using rows and expanded. Everything works except onLongPress (or onDoubleTap). What am I doing wrong, do I have to rebuild the entire code in a different format, or am I overcomplicating this?

I also tried to add a new child (error: already defined), GestureDetector, InkWell, with no success.

body: SingleChildScrollView(
      child: Container(
        child: Column(
          children: <Widget>[
            Center(
                child: Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    crossAxisAlignment: CrossAxisAlignment.center,
                    children: <Widget>[
                  Expanded(
                      child: FlatButton(               
                          onPressed: () {
                            setState(() {
                              launchURL();
                            });
                          },  

                          //Trying to add onLongPress , error: "onLongPress not defined
                          //If I try add a new child it says child already defined

                          onLongPress: () => _showAlertMessage(context, "message"),


                          padding: EdgeInsets.all(6.0),
                          child: Image.asset(
                            'images/image1.png',
                          ))),

                  Expanded(
                      child: FlatButton(                     
                          onPressed: () {
                            setState(() {
                              launchURL();
                            });
                          },
                          padding: EdgeInsets.all(6.0),
                          child: Image.asset(
                            'images/image2.png',
                          )
                      )//flat button
                  ),//expanded
                ])), //row-center

                //Repeat above for rows of 2 more image buttons

The code runs with a single onPressed for each button and does not display any errors, but adding any second click event displays errors.

Answer 1

Flatbutton only supports the onPressed callback, not onLongpressed, etc. Suggest you re-look at using gesture detector or other widgets that support long press. I would try using two containers, each wrapped in a gesture detector widget, as children in the row. Each container having a text and/or image content. You can then pick up onTap, double tap, long press, etc on each container. Not tested this as I am on my phone but should work. They are probably more elegant widgets to use than container.