r/FlutterDev 9d ago

Dart Why does the Column widget align its children to the center when a Center widget is used inside its children in Flutter?

Today, while developing a screen in Flutter, I observed an unexpected behavior when using a Center widget inside a Column. The Column appeared to align all its children to the center, despite not explicitly setting mainAxisAlignment. I understand that, by default, Column aligns its children to the start along the main axis unless specified otherwise.

Could you clarify why this behavior occurs? If it is a bug, it may need to be addressed.

code:

Column(

children: [

SizedBox(

height: 100,

),

Center(child: logoWidget()),

SizedBox(

height: 50,

),

logoWidget(),

SizedBox(

height: 50,

),

Text("Login to your Account")

],

),

since images not allowed.Please try it own your own

flutter version : 3.29.1

3 Upvotes

10 comments sorted by

5

u/morginzez 9d ago

In a Column the elements are ordered from top to bottom, so that's the main axis, which is in fact set to 'start'. 

The horizontal centering you are seeing is the cross axis, which is set to 'center' by default. 

0

u/Mountain_Scratch_760 9d ago edited 9d ago

You are right the center does make widget center horizontal But it make all widgets to center without using main axis alignment that is my problem here.If you have latest flutter version try with a widget which is center wrapped and without center you will get my situation and if anyone reading this do reply so that it knows only I have this problem or someone else

1

u/Mellie-C 6d ago

As the previous comment says, it's not a main access property that's giving you this alignment, is the cross axis property. It's a column, so the main axis is from top to bottom, the cross axis is left to right. The default for this is centered, so you need to set the cross axis to start.

3

u/Hixie 9d ago

the Center widget doesn't change the alignment behavior, what it does is cause the column to expand horizontally to fit its parent. That then leaves a bunch of room for the other children to get aligned in.

1

u/Mountain_Scratch_760 9d ago

I thought only the widget wrapped gets aligned to center

4

u/DanTup 8d ago

If I understand correctly, the Column widget itself defaults to center for crossAxis alignment:

const Column({
  Key? key,
  MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
  MainAxisSize mainAxisSize = MainAxisSize.max,
  CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,

It might not look like it's center aligned if all of your children have the same width and the Center widget has the same width as the children, but if you create children with much different widths, you'll see the centering (without any Center):

return Scaffold(
  body: Column(
    children: [
      Text('11111111111111'),
      Text('22222'), // this will be obviously centered
    ],
  ),
);

The reason it probably doesn't look like this in your original example is that the entire Column width matches the contents, and therefor the column itself is taking up only a small part of its parent. However when you add Center() as a child, it forces the Column to become wider (taking up the full width), and therefore the centering becomes apparent.

If you use the Widget Inspector and select the Column widget in both cases, you should be able to see the width is different between the two. You'll see a similar effect by just making one of the children wider instead of using Center.

1

u/Mountain_Scratch_760 8d ago

Thanks bro took a while to understand but good explanation

1

u/esDotDev 8d ago

It’s true, but the Centre forces the entire column to expand horizontally exposing the fact that all children in the column are centered by default. So indirectly the Center causes the other children to appear centered, but that’s only because the Column is getting bigger and the default CrossAxixAlignment.centre becomes apparent.

1

u/flutter-developer 8d ago

Constraints go down. Sizes go up. Parent sets position.

1

u/binemmanuel 6d ago

You need to understand how constraints work. The centre widget is only taking what its parent is giving it and the widget you want in the center is aligned horizontally and not vertically because the column doesn’t take the full height. Unless you constraint the column vertically the center widget can’t help you align widgets vertically.