从 Flutter 开始：如何让 4 个按钮填充一个 SafeArea

Question

I've very much a beginner in Dart and Flutter, and my project is to learn while building an app. I've learned the basics with an online class and I have basis in Java.

Now, in my homepage, I'm trying to have 4 buttons take the whole screen. My current layout is to have them all take an equal amount of space and be stacked vertically. Problem is, I can't find a way to make the RaisedButton fill automatically. I've tried retrieving the height of the screen and dividing that between the buttons but it's not working. Here's how I do it : First, the homescreen layout:

class Homescreen extends StatelessWidget {
  Widget build(context) {
    double height = MediaQuery.of(context).size.height - 60;
    return Scaffold(
      body: SafeArea(
        child: ListView(
          children: [
            PlanningButton(height),
            Container(margin: EdgeInsets.only(top: 20.0)),
            BookingButton(height),
            Container(margin: EdgeInsets.only(top: 20.0)),
            ModifyButton(height),
            Container(margin: EdgeInsets.only(top: 20.0)),
            CancelButton(height),
          ],
        ),
      ),
    );
  }

As you can see, I pass the height argument to my buttons all built around this model:

  Widget PlanningButton(double pixel_y) {
    return RaisedButton(
      padding: EdgeInsets.all(pixel_y / 8.0),
      onPressed: () {}, //goes to the planning screen
      color: Colors.blue[200],
      child: Text("Planning"),
    );
  }

Yet, it's never quite right. I don't think it's taking into account the notification bar or the navigation bar. I suspect there is a workaround that involves wrapping the buttons into a container or using a different kind of widget that have button-like properties but I can't find what suits my needs.

Thanks for any help !

edit: I'm basically trying to do this

Answer 1

Try removing the variable height logic, and simply wrap your buttons in Expanded widgets. This is pretty much what it was built for.

Check it out here: https://api.flutter.dev/flutter/widgets/Expanded-class.html

Answer 2

If 4 buttons are the only widgets, you dont need to use ListView just use a Column with mainAxisAlignment: MainAxisAlignment.spaceEvenly

class Sample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            Expanded(
              child: Container(
                color: Colors.red,
                child: Center(
                  child: RaisedButton(
                    onPressed: () {},
                    child: Text("button"),
                  ),
                ),
              ),
            ),
            Expanded(
              child: Container(
                color: Colors.blue,
                child: Center(
                  child: RaisedButton(
                    onPressed: () {},
                    child: Text("button"),
                  ),
                ),
              ),
            ),
            Expanded(
              child: Container(
                color: Colors.green,
                child: Center(
                  child: RaisedButton(
                    onPressed: () {},
                    child: Text("button"),
                  ),
                ),
              ),
            ),
            Expanded(
              child: Container(
                color: Colors.yellow,
                child: Center(
                  child: RaisedButton(
                    onPressed: () {},
                    child: Text("button"),
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

Answer 3

You could use a Column and Expanded to do the job. If you want to make your Column scrollable, you can wrap it with SingleChildScrollView . I used SizedBox instead of Container to make the spacing because it is way more efficient and is designed for it.

class Homescreen extends StatelessWidget {
  Widget build(context) {
    double height = MediaQuery.of(context).size.height - 60;
    return Scaffold(
      body: SafeArea(
        child: Column(
          children: <Widget>[
            Expanded(
              child: PlanningButton(height)
            ),
            SizedBox(height:20),
            Expanded(
              child: BookingButton(height),
            ),
            SizedBox(height:20),
            Expanded(
              child: ModifyButton(height),
            ),
            SizedBox(height:20),
            Expanded(
              child: CancelButton(height),
            ),
          ],
        ),
      ),
    );
  }

Answer 4

Before you read this, it's not the best way to do things but it's one I'm using at least for prototyping. You may find using a container with a list and the argument MainAxisAlignment to work better for you.

A lot of comments here might give a solution that works for you but here's mine. I got it to work like I wanted by using SizedBox .

First, I recovered the width of the screen, then I created the buttons and put them into SizedBox fitting the screen's width, I put them in a Column and I added a few Container for the style points.

Result:

Code :

class Homescreen extends StatelessWidget {
  Widget build(context) {
    double width = MediaQuery.of(context).size.width; //getting screen width
    return Scaffold(
      body: SafeArea(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Container(margin: EdgeInsets.only(bottom: 20.0)),
            PlanningButton(width),
            Container(margin: EdgeInsets.only(bottom: 20.0)),
            BookingButton(width),
            Container(margin: EdgeInsets.only(bottom: 20.0)),
            ModifyButton(width),
            Container(margin: EdgeInsets.only(bottom: 20.0)),
            CancelButton(width),
            Container(margin: EdgeInsets.only(bottom: 20.0)),
          ],
        ),
      ),
    );
  }

  Widget PlanningButton(double width) {
    return Expanded(
      child: SizedBox(
        width: width - 20,
        child: RaisedButton(
          onPressed: () {},
          color: Colors.blue,
          child: Text(
            "planning",
            textScaleFactor: 4.0,
          ),
        ),
        //fit: BoxFit.cover,
      ),
    );
  }

The user can tap anywhere on the colored buttons and it will register. Now I'll add images and transparency to make it look good!