In Android match_parent and wrap_content are used to resize the widgets automatically relative to their parent to the content the widget contains.

In Flutter it seems by default all widgets are set to wrap_content, how would I change it such that I can fill its width and height to that of its parent?

13 Answers

You can do with little Trick: Suppose you have requirement of : ( Width,Height )

Wrap_content ,Wrap_content :

 //use this as child Wrap( children: <Widget>[*your_child*]) 

Match_parent,Match_parent:

 //use this as child Container( height: double.infinity, width: double.infinity,child:*your_child*) 

Match_parent,Wrap_content :

 //use this as child Row( mainAxisSize: MainAxisSize.max, children: <Widget>[*your_child*], ); 

Wrap_content ,Match_parent:

 //use this as child Column( mainAxisSize: MainAxisSize.max, children: <Widget>[your_child], ); 

In order to get behavior for match_parent and wrap_content we need to use mainAxisSize property in Row/Column widget, the mainAxisSize property takes MainAxisSize enum having two values which is MainAxisSize.min which behaves as wrap_content and MainAxisSize.max which behaves as match_parent.

Link of the original Article

The short answer is that the parent doesn't have a size until the child has a size.

The way layout works in Flutter is that each widget provides constraints to each of its children, like "you can be up to this wide, you must be this tall, you have to be at least this wide", or whatever (specifically, they get a minimum width, a maximum width, a minimum height, and a maximum height). Each child takes those constraints, does something, and picks a size (width and height) that matches those constraints. Then, once each child has done its thing, the widget can can pick its own size.

Some widgets try to be as big as the parent allows. Some widgets try to be as small as the parent allows. Some widgets try to match a certain "natural" size (e.g. text, images).

Some widgets tell their children they can be any size they want. Some give their children the same constraints that they got from their parent.

There are actually some options available:

You can use SizedBox.expand to make your widget match parents dimensions, or SizedBox(width: double.infinity) to match only the width or SizedBox(heigth: double.infinity) to match only the heigth.

If you want a wrap_content behavior it depends on the parent widget you are using, for example if you put a button on a column it will behave like wrap_content and to use it like match_parent you can wrap the button with a Expanded widget or a sizedbox.

With a ListView the button gets a match_parent behavior and to get a wrap_content behavior you can wrap it with a Flex widget like Row.

Using an Expanded widget makes a child of a Row, Column, or Flex expand to fill the available space in the main axis (e.g., horizontally for a Row or vertically for a Column).

Using a Flexible widget gives a child of a Row, Column, or Flex the flexibility to expand to fill the available space in the main axis (e.g., horizontally for a Row or vertically for a Column), but, unlike Expanded, Flexible does not require the child to fill the available space.

Use the widget Wrap.

For Column like behavior try:

 return Wrap( direction: Axis.vertical, spacing: 10, children: <Widget>[...],); 

For Row like behavior try:

 return Wrap( direction: Axis.horizontal, spacing: 10, children: <Widget>[...],); 

For more information: Wrap (Flutter Widget)

I used this solution, you have to define the height and width of your screen using MediaQuery:

 Container( height: MediaQuery.of(context).size.height, width: MediaQuery.of(context).size.width ) 

A simple workaround:

If a container has only one top level child, then you can specify alignment property for the child and give it any available value. it'll fill all the space in the container.

Container(color:Colors.white,height:200.0,width:200.0, child:Container( color: Colors.yellow, alignment:Alignment.[any_available_option] // make the yellow child match the parent size ) ) 

Another way:

Container(color:Colors.white,height:200.0,width:200.0, child:Container( color: Colors.yellow, constraints: BoxConstraints.expand(height: 100.0), // height will be 100 dip and width will be match parent ) ) 

Stack( children: [ Container(color:Colors.red, height:200.0, width:200.0), Positioned.fill( child: Container(color: Colors. yellow), ) ] ), 

To make a child fill its parent, simply wrap it into a FittedBox

 FittedBox( child: Image.asset('foo.png'), fit: BoxFit.fill, ) 

Use FractionallySizedBox widget.

FractionallySizedBox( widthFactor: 1.0, // width w.r.t to parent heightFactor: 1.0, // height w.r.t to parent child: *Your Child Here* } 

This widget is also very useful when you want to size your child at a fraction of its parent's size.

Example:

If you want the child to occupy 50% width of its parent, provide widthFactor as 0.5

Match Parent

To match or fill the parent (height & width) we can use additional constraints on Container:

Container( constraints: BoxConstraints.expand(), // ← this guy child: Text('Center > Container > Text') ) 

In Flutter, constraints are the space you can fill (or must fill, if "tight" constraints).

Constraints are given... no actually, imposed by parents.

By default, Container will wrap its content (child:) & size itself to its child, unless overriden (or not allowed by tight constraints).

Using the constraints: argument, we can give Container additional constraints to override default Container constraint behavior (such as wrapping content).

Using Container(constraints: BoxConstraints.something) doesn't overwrite incoming/parent constraints; It just allows us to override default behavior, where allowed, such as wrapping content.

Code Sample - BoxConstraints

Here's a copy/paste code example showing effects of various constraints we can apply to a Container that has "loose" incoming/parental constraints (provided by Center).

import 'package:flutter/material.dart'; class MatchParentPage extends StatefulWidget { @override _MatchParentPageState createState() => _MatchParentPageState(); } class _MatchParentPageState extends State<MatchParentPage> { BoxConstraints constraints; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text('Match Parent'), ), body: Column( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ Expanded( // shares space constraint evenly with other Expanded child: Center( // ← fills tight parent constraint & loosens ↓ child constraint ↓ child: Container( // got loose constraint from Center... constraints: constraints, // can apply many additional constraints color: Colors.lightBlueAccent.withOpacity(.3), child: Text('Center > Container > Text')), ), ), Expanded( child: Container( color: Colors.orangeAccent, child: Wrap( children: [ _button('default', null), _button('*expand()', BoxConstraints.expand()), _button('*tight(Size.infinite)', BoxConstraints.tight(Size.infinite)), _button('tight(Size.zero)', BoxConstraints.tight(Size.zero)), _button('tight(Size.fromHeight(100))', BoxConstraints.tight(Size.fromHeight(100))), _button('tight(Size.fromWidth(100))', BoxConstraints.tight(Size.fromWidth(100))), _button('tightForFinite(width: 100, height: 100)', BoxConstraints.tightForFinite(width: 100, height: 100)), _button('loose(Size.infinite)', BoxConstraints.loose(Size.infinite)), _button('tightFor(width: double.infinity)', BoxConstraints.tightFor(width: double.infinity)), _button('tightFor(height: double.infinity)', BoxConstraints.tightFor(height: double.infinity)), ]) ), ) ], ), ); } Widget _button(String label, BoxConstraints _constraints) { bool _active = _constraints == constraints; return Padding( padding: const EdgeInsets.only(top:8, left: 8), child: RaisedButton( color: _active ? Colors.cyanAccent : null, child: Text(label), onPressed: () { setState(() => constraints = _constraints); }, ), ); } } 

Use this line of codes inside the Column. For wrap_content : mainAxisSize: MainAxisSize.min For match_parent : mainAxisSize: MainAxisSize.max

MATCH_PARENT

FractionallySizedBox( widthFactor: 1.0, // width w.r.t to parent heightFactor: 1.0, // height w.r.t to parent child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ) 

OR

Container( height: double.infinity, width: double.infinity, child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ) 

OR

Container( height: MediaQuery.of(context).size.height, width: MediaQuery.of(context).size.width, child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ) 

OR

Container( constraints: BoxConstraints.expand(), child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ) 

WRAP_CONTENT

Wrap(children: [ Container( child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ), ]) 

OR

Container( constraints: BoxConstraints.tightFor(), child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ) 

Match_parent,Wrap_content :

Row( children: [ Expanded( child: Container( child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ), ), ]) 

Wrap_content,Match_parent :

Column( children: [ Expanded( child: Container( child: ElevatedButton( onPressed: () {}, child: Text("+"), ), ), ), ])