Flutter : How to set height for my TextField without make my screen bug?

I want to add a textfield inside my row.....

Widget build(BuildContext context) {
    return 
      SingleChildScrollView(
        child: Column(
          children: [
            Row(
              children: [
                  Image.asset("assets/cross.png"),
                  Text("Nouveau contact"),
              ]
            ),
            Row(
              children: [
                Radio(value: "Homme", groupValue: gender, onChanged: (value) { setState(() { gender = value; }); }),
                Text("Homme"),
                Divider(indent: 10.0,),
                Radio(value: "Femme", groupValue: gender, onChanged: (value) { setState(() { gender = value; }); }),
                Text("Femme"),
              ],
            ),
            Row(
              children: [
                //NOTHING HERE
              ],
            ),
            Row(),
          ],
        ),
      );
  }

Here, the display is good

But here

Widget build(BuildContext context) {
    return 
      SingleChildScrollView(
        child: Column(
          children: [
            Row(
              children: [
                  Image.asset("assets/cross.png"),
                  Text("Nouveau contact"),
              ]
            ),
            Row(
              children: [
                Radio(value: "Homme", groupValue: gender, onChanged: (value) { setState(() { gender = value; }); }),
                Text("Homme"),
                Divider(indent: 10.0,),
                Radio(value: "Femme", groupValue: gender, onChanged: (value) { setState(() { gender = value; }); }),
                Text("Femme"),
              ],
            ),
            Row(
              children: [
                TextField(
                  maxLines: 1,
                  controller: TextEditingController(
                    text: firstname
                  ),
                  decoration: InputDecoration(
                    hintText: "Prénom"
                  ),
                ),
              ],
            ),
            Row(),
          ],
        ),
      );
  }

The display is bugged just because I added a TextField, but.. why ?

I want the textfield can be added without bug my display instead of having a white screen when I add my textfield.....

I really don't understand why

If you look in your console you should be able to see why it's wrong. It should say something like

> "An InputDecorator, which is typically created by a TextField, cannot
> have an unbounded width.\nThis happens when the parent widget does not
> provide a finite width constraint. For example, if the InputDecorator
> is contained by a Row, then its width must be constrained. An Expanded
> widget or a SizedBox can be used to constrain the width of the
> InputDecorator or the TextField that contains it."

So to solve it you can do what is suggested by writing

Row(
  children: [
    Expanded(
      child: TextField(
        maxLines: 1,
        controller: TextEditingController(
            text: firstname
        ),
        decoration: InputDecoration(
            hintText: "Prénom"
        ),
      ),
    ),
  ],
),

To try to explain it a bit simplified. A Row tells their children: "Take all the space you want, there is no limit". And a TextField by default wants all available space. This doesn't work together. An Expanded is a widget that makes sure that its child knows how much space there really is.