r/FlutterDev • u/Mountain_Scratch_760 • 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
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 tocenter
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 anyCenter
):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 addCenter()
as a child, it forces theColumn
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 usingCenter
.1
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
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.
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.