Develop Reference

Container is wrap the text widget but why the button widget get affected by the textAlign?

Sir, In code I am wrapping the only Text widget. After that I used some custom style like text align. But after use I expected to center only the text part because only this widget get wrapped not to the other. But I saw my button also get centered. How it possible? I was wrapped one widget but my other widget get affected. What's logic into there, sir?

You need to set a crossAxisAlignment: CrossAxisAlignment.start, and wrap the headline text with center widget. hope the below code can show you a good example.
class Demo extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("title"),
),
body: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Center(
child: Text("Whats your favourite food?"),
),
RaisedButton(
onPressed: () {},
child: Container(
padding: EdgeInsets.zero,
decoration: BoxDecoration(),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text("Answer 1"),
),
),
),
RaisedButton(
onPressed: () {},
child: Container(
padding: EdgeInsets.zero,
decoration: BoxDecoration(),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text("Answer 1"),
),
),
),
RaisedButton(
onPressed: () {},
child: Container(
padding: EdgeInsets.zero,
decoration: BoxDecoration(),
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text("Answer 1"),
),
),
),
],
),
);
}
}

Set column widget's mainaxisalignement to start, or wrap all widget that you don't want to center in a column

Text is placed on the screen but it scroll

android studio 3.6
I need to scroll text only if text does not fit the screen. So if text is placed on the screen it MUST NOT scroll.
snippet:
class MainScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor: Colors.orange,
body: SafeArea(
child: SingleChildScrollView(
child: new Container(
color: Colors.white,
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: new Column(
children: [
new Text("column_1", style: TextStyle(backgroundColor: Colors.yellow)),
new Text("column_2", style: TextStyle(backgroundColor: Colors.blue)),
new Text("column_3", style: TextStyle(backgroundColor: Colors.black12))])))));
}
}
result
but I can scroll. Why?

It is scrolling as your column sits inside a singleChildScrollView() which enables scrolling by default.
As our container was using a MediaQuery to set its height, the singleChildScrollView() has no vertical space to expand into and thus resulted in the scrolling behaviour.
Instead we should wrap our singleChildScrollView() inside a container and then perform the MediaQuery on that container instead.
Please see the below code:
return new Scaffold(
backgroundColor: Colors.orange,
body: SafeArea(
child: Container(
color: Colors.white,
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: SingleChildScrollView(
child: new Container(
child: new Column(
children: [
new Text(
"column_1",
style: TextStyle(backgroundColor: Colors.yellow),
),
new Text(
"column_2",
style: TextStyle(backgroundColor: Colors.blue),
),
new Text(
"column_3",
style: TextStyle(backgroundColor: Colors.black12),
),
],
),
),
),
),
),
);

Here my solution
class MainScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor: Colors.white,
body: SafeArea(
child: SingleChildScrollView(
child: new Column(children: [
new Container(height: 64.0, color: Colors.blue),
new Container(
height: Constants.CARD_VIEW_HEIGHT, color: Colors.yellow),
new Container(height: 356.0, color: Colors.red)
]))));
}
}

ListView is the simplest answer I think;
class MainScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor: Colors.orange,
body: SafeArea(
child: new Container(
color: Colors.red,
height: MediaQuery.of(context).size.height,
width: MediaQuery.of(context).size.width,
child: new ListView(
shrinkWrap: true,
children: [
Center(child: new Text("column_1", style: TextStyle(backgroundColor: Colors.yellow))),
Center(child: new Text("column_2", style: TextStyle(backgroundColor: Colors.blue))),
Center(child: new Text("column_3", style: TextStyle(backgroundColor: Colors.black12)))]))));
}
}

Maybe use height and width on the ScrollView itself, rather than Column. The Column is taking more space on screen, causing it to scroll.

SingleChildScrollView inside Row

I have a layout made of a Column, one of its elements being a row (so that it takes the full width of the screen). Inside that row, I have a wrap, which content is pretty big and that I want to put inside a SingleChildScrollView.
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Container(
padding: const EdgeInsets.all(kPaddingMainContainer),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Title', style: Theme.of(context).textTheme.title)
],
),
Padding(
padding: const EdgeInsets.only(top: 10),
),
Row(
children: <Widget>[
Expanded(
child: SingleChildScrollView(
child: Wrap(
alignment: WrapAlignment.center,
runSpacing: 20.0, // distance between rows
spacing: 30.0, // distance between chips
children: _getWidgets(),
),
),
),
],
),
],
),
),
),
);
}
With this code, I can't get the SingleChildScrollView to make the wrap scrollable. Instead, I got a RenderFlex overflowed error.
However, if I extract the wrap from the Row, as follow:
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Container(
padding: const EdgeInsets.all(kPaddingMainContainer),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Title', style: Theme.of(context).textTheme.title)
],
),
Padding(
padding: const EdgeInsets.only(top: 10),
),
Expanded(
child: SingleChildScrollView(
child: Wrap(
alignment: WrapAlignment.center,
runSpacing: 20.0, // distance between rows
spacing: 30.0, // distance between chips
children: _getWidgets(),
),
),
),
]),
),
),
);
}
Then, the scroll is working.
However, now the wrap doesn't expand to full width anymore, what I want.
How to use the SingleChildScrollView inside a Row ?
PS: I don't want to wrap the Column in a SingleChildScrollView as I want my title to stay fixed and only the wrap below to scroll.

I found a solution by wrapping the Wrap in a ConstrainedBox (instead of a row) for which the minWidth is the width of the screen.
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Container(
padding: const EdgeInsets.all(kPaddingMainContainer),
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('Title', style: Theme.of(context).textTheme.title)
],
),
Padding(
padding: const EdgeInsets.only(top: 10),
),
Expanded(
child: SingleChildScrollView(
child: ConstrainedBox(
constraints: BoxConstraints(
minWidth: MediaQuery.of(context).size.width,
),
child: Wrap(
alignment: WrapAlignment.center,
runSpacing: 20.0, // distance between rows
spacing: 30.0, // distance between chips
children: _getWidgets(),
),
),
),
),
]),
),
),
);
}
This fixed my issue and I can now scroll the Wrap widget only by tapping anywhere on the screen, while the first row with the title stays fixed.

How to set a BackdropFilter using dynamic-sized widgets in Flutter

I have a column: header with text, body with image, footer with text, all widgets have transparent backgrounds.
I want to set the background using a blur of the main image but I keep reaching dead ends.
In some situations this would be straight forward but in my scenario the image could be of any size and aspect ratio, and I need the effect to be wrapped with the column.
Here are my two failed attempts:
Method 1
I have a Stack with the image as the first item, then a BackdropFilter with ImageFilter blur, then my Column.
This works but the Image bleeds out from under the Column because of the image size (which can be any size).
I want to constrain it to the height of my Column.
return Container(
child: Stack(
alignment: AlignmentDirectional.topCenter,
children: <Widget>[
Positioned.fill(child: Image.network(_imgUrl)),
BackdropFilter(
filter: ImageFilter.blur(sigmaX: 10.0, sigmaY: 10.0),
child: Container(
decoration: BoxDecoration(color: Colors.white.withOpacity(0.0)),
)),
Container(
child: Column(
mainAxisSize: MainAxisSize.min,
// https://stackoverflow.com/a/41846093/3429021
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Header(),
BodyPhoto(),
Footer()
],
),
),
],
),
Method 2
Putting the column in a Container with a DecorationImage, which sizes the image perfectly, but I have no way of applying the blur effect.
(_streamItem is my Column wrapped in a container)
body: Container(child: _streamItem,
decoration: new BoxDecoration(image: DecorationImage(
image: NetworkImage(_streamItem.imgUrl),
fit: BoxFit.cover)
)
)
Any ideas?

I think you can consider using Positioned widget - it has width and height property. We can combine these widgets: Positioned > ClipRect > BackdropFilter. Please refer to the Gist: https://gist.github.com/anticafe/dc84cf6488d9defea437b702b13e2749#file-blur_multiple_widgets_with_dynamic_region-dart
Let take a look at this article to see more about BackdropFilter.

You can explicitly give a fix height to the container that contains the image, which will even look better.
In this example I have set three images of very different dimensions and has no problem rendering.
Refer the below code:
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('So Help'),
),
body: new ListView(
children: <Widget>[
MyContainer(
imageUrl:
'https://i.dailymail.co.uk/i/pix/2017/01/16/20/332EE38400000578-4125738-image-a-132_1484600112489.jpg',
),
MyContainer(
imageUrl:
'http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2014/4/11/1397210130748/Spring-Lamb.-Image-shot-2-011.jpg',
),
MyContainer(
imageUrl:
'http://wackymania.com/image/2011/6/vertical-panoramic-photography/vertical-panoramic-photography-15.jpg',
),
],
),
);
}
}
class MyContainer extends StatelessWidget {
final String imageUrl;
MyContainer({#required this.imageUrl});
#override
Widget build(BuildContext context) {
return new Container(
height: 300.0,
child: new Stack(
children: <Widget>[
new Container(
child: Image.network(
this.imageUrl,
width: MediaQuery.of(context).size.width,
fit: BoxFit.cover,
),
),
BackdropFilter(
filter: Dui.ImageFilter.blur(sigmaX: 10.0, sigmaY: 10.0),
child: new Container(
color: Colors.transparent,
),
),
new Container(
height: 300.0,
child: new Column(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: MediaQuery.of(context).size.width,
),
Padding(
padding: const EdgeInsets.all(20.0),
child: new Text(
'Header',
style: new TextStyle(color: Colors.white),
),
),
new Expanded(
child: Image.network(imageUrl),
),
Padding(
padding: const EdgeInsets.all(20.0),
child: new Text(
'Footer',
style: new TextStyle(color: Colors.white),
),
),
],
),
)
],
),
);
}
}

Android TextView's Lines equivalent in flutter

So, I need to make a Text widget to have an exact number of lines. In android studio, I only need to add property android:Lines = 2 and then the TextView will be 2 lines, regardless of how long the text is (if less than 2 lines, then fill the second line with an empty space) and regardless of what's the user's device font size.
The problem is, I have difficulty in replicating such behavior in flutter dynamically. The screenshot below works only on a particular user device's fontSize, since it uses an exact height (32.0).
new Container(
height: 32.0,
child: new Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new Expanded(
child: new Text('Curry Rice'), maxLines: 2, overflow: TextOverflow.ellipsis))
])
)
The problem arise when user is increasing / decreasing their device's font size, it will make the fixed-height container's doesn't work anymore.
So, any idea how to replicate android:Lines behavior in flutter Text widget regardless of the user's device text size?
UPDATE: Added comprehensive code for better context
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
// final wordPair = new WordPair.random();
return new MaterialApp(
title: 'App Title',
theme:
new ThemeData(primaryColor: Colors.white, accentColor: Colors.blue),
home: new Scaffold(
appBar: new AppBar(
title: new Text('App Title'),
actions: <Widget>[
new IconButton(icon: new Icon(Icons.list), onPressed: null),
],
),
body: new Center(
child: new Padding(
padding: new EdgeInsets.all(16.0),
child: new TestWidget()))));
}
}
class TestWidget extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new SizedBox(
width: 150.0,
child: new Card(
child: new Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
new Image.asset(
'assets/thumb2.jpg',
color: Colors.red,
),
new InkWell(
onTap: () {
// _showMenuDescription(context);
},
child: new Padding(
padding: new EdgeInsets.all(8.0),
child: new Column(
children: <Widget>[
new Container(
height: 32.0,
child: new Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
new Expanded(
child: new Text(
'Curry Rice With Tandoori Chicken and Sunny Side Fried Egg',
maxLines: 2,
overflow: TextOverflow.ellipsis),
)
]),
),
new Container(height: 8.0),
new Row(
children: <Widget>[
new Expanded(
child: new Text(
'BBQ Sauce',
maxLines: 1,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.black45),
),
),
new Padding(
padding: new EdgeInsets.only(left: 8.0),
child: new Text(
'20,000',
maxLines: 1,
overflow: TextOverflow.ellipsis,
textAlign: TextAlign.end,
style: new TextStyle(
color: const Color(0xffffa000)),
))
],
),
],
))),
],
),
));
}
}

The problem is that you are setting a finite height for your column. And that height is not enough to display 2 lines with this text style.
Increase the column height or remove that constraint entirely should solve the problem.