I&#39;m using Flutter and I&#39;d like to add a border to a widget (in this case, a `Text` widget).

I tried `TextStyle` and `Text`, but I didn&#39;t see how to add a border.


How can I add a border to a widget in Flutter?

I&#39;m trying to construct a simple login page for my Flutter app.  I&#39;ve successfully built the TextFields and log in/Sign in buttons.  I want to add a horizontal ListView.  When I run the code my elements disappear, if I do it without the ListView, it&#39;s fine again. How can I do this correctly?

&lt;!-- language: dart --&gt;

    return new MaterialApp(
            home: new Scaffold(
              appBar: new AppBar(
                title: new Text(&quot;Login / Signup&quot;),
              ),
              body: new Container(
                child: new Center(
                  child: new Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                    children: &lt;Widget&gt;[
                      new TextField(
                        decoration: new InputDecoration(
                          hintText: &quot;E M A I L    A D D R E S S&quot;
                        ),
                      ),
                      new Padding(padding: new EdgeInsets.all(15.00)),
                      new TextField(obscureText: true,
                        decoration: new InputDecoration(
                          hintText: &quot;P A S S W O R D&quot;
                        ),
                        ),
                      new Padding(padding: new EdgeInsets.all(15.00)),
                      new TextField(decoration: new InputDecoration(
                        hintText: &quot;U S E R N A M E&quot;
                      ),),
                      new RaisedButton(onPressed: null,
                      child:  new Text(&quot;SIGNUP&quot;),),
                      new Padding(padding: new EdgeInsets.all(15.00)),
                      new RaisedButton(onPressed: null,
                      child: new Text(&quot;LOGIN&quot;),),
                      new Padding(padding: new EdgeInsets.all(15.00)),
                      new ListView(scrollDirection: Axis.horizontal,
                      children: &lt;Widget&gt;[
                        new RaisedButton(onPressed: null,
                        child: new Text(&quot;Facebook&quot;),),
                        new Padding(padding: new EdgeInsets.all(5.00)),
                        new RaisedButton(onPressed: null,
                        child: new Text(&quot;Google&quot;),)
                      ],)
    
                    ],
                  ),
                ),
                margin: new EdgeInsets.all(15.00),
              ),
            ),
          );

How to add a ListView to a Column in Flutter?

For various reasons, sometimes the `build` method of my widgets is called again. 

I know that it happens because a parent updated. But this causes undesired effects. 
A typical situation where it causes problems is when using `FutureBuilder` this way:


    @override
    Widget build(BuildContext context) {
      return FutureBuilder(
        future: httpCall(),
        builder: (context, snapshot) {
          // create some layout here
        },
      );
    }

In this example, if the _build_ method were to be called again, it would trigger another HTTP request. Which is undesired.


Considering this, how to deal with the unwanted build? Is there any way to prevent a build call?

How to deal with unwanted widget build?

I have realized that it is possible to create widgets using plain functions instead of subclassing [StatelessWidget](https://docs.flutter.io/flutter/widgets/StatelessWidget-class.html). An example would be this: 

    Widget function({ String title, VoidCallback callback }) {
      return GestureDetector(
        onTap: callback,
        child: // some widget
      );
    }


This is interesting because it requires _far_ less code than a full-blown class. Example:


    class SomeWidget extends StatelessWidget {
      final VoidCallback callback;
      final String title;

      const SomeWidget({Key key, this.callback, this.title}) : super(key: key);

      @override
      Widget build(BuildContext context) {
          return GestureDetector(
            onTap: callback,
            child: // some widget
          );
      }
    }


So I&#39;ve been wondering: Is there any difference besides syntax between functions and classes to create widgets? And is it a good practice to use functions?

What is the difference between functions and classes to create reusable widgets?

Working on my first flutter app. The main app screen doesn&#39;t have this issue, all the texts show up as they should.

However in this new screen I&#39;m developing, all the text widget have some weird yellow line / double-line underneath.

Any ideas on why this is happening?

[![Yellow Lines][1]][1]


  [1]: https://i.stack.imgur.com/pAmad.jpg

Yellow lines under Text Widgets in Flutter?

How would you approach adding a splash screen to Flutter apps? It should load and display before any other content. Currently, there is a brief flash of color before the Scaffold(home:X) widget loads.

Adding a splash screen to Flutter apps

In Android, every single `View` subclass has a `setVisibility()` method that allows you modify the visibility of a `View` object

There are 3 options of setting the visibility:

- Visible: Renders the `View` visible inside the layout
- Invisible: Hides the `View`, but leaves a gap that is equivalent to what the `View` would occupy if it were visible
- Gone: Hides the `View`, and removes it entirely from the layout. It&#39;s as if its `height` and `width` were `0dp`

Is there something equivalent to the above for Widgets in Flutter?

For a quick reference:
https://developer.android.com/reference/android/view/View.html#attr_android:visibility

How to show/hide widgets programmatically in Flutter

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?



The equivalent of wrap_content and match_parent in flutter?

I&#39;ve used both `Expanded` and `Flexible` widgets and they both seem to work the same.

What is the difference between Expanded and Flexible?



Flutter: Expanded vs Flexible

I don&#39;t understand how `LayoutBuilder` is used to get the height of a Widget. 

I need to display the list of Widgets and get their height so I can compute some special scroll effects. I am developing a package and other developers provide widget (I don&#39;t control them). I read that LayoutBuilder can be used to get height. 

In very simple case, I tried to wrap Widget in LayoutBuilder.builder and put it in the Stack, but I always get `minHeight` `0.0`, and `maxHeight` `INFINITY`. Am I misusing the LayoutBuilder?

**EDIT**: It seems that LayoutBuilder is a no go. I found the [CustomSingleChildLayout][1] which is almost a solution. 

I extended that delegate, and I was able to get the height of widget in `getPositionForChild(Size size, Size childSize)` method. BUT, the first method that is called is `Size getSize(BoxConstraints constraints)` and as constraints, I get 0 to INFINITY because I&#39;m laying these CustomSingleChildLayouts in a ListView.

My problem is that SingleChildLayoutDelegate `getSize` operates like it needs to return the height of a view. I don&#39;t know the height of a child at that moment. I can only return constraints.smallest (which is 0, the height is 0), or constraints.biggest which is infinity and crashes the app.

In the docs it even says: 

&gt; ...but the size of the parent cannot depend on the size of the child.

And that&#39;s a weird limitation.

  [1]: https://docs.flutter.io/flutter/widgets/CustomSingleChildLayout-class.html

How to get height of a Widget?

What is the correct way to use an InheritedWidget? So far I understood that it gives you the chance to propagate data down the Widget tree. In extreme if you put is as RootWidget it will be accessible from all Widgets in the tree on all Routes, which is fine because somehow I have to make my ViewModel/Model accessible for my Widgets without having to resort to globals or Singletons.

BUT InheritedWidget is immutable, so how can I update it? And more important how are my Stateful Widgets triggered to rebuild their subtrees?

Unfortunately the documentation is here very unclear and after discussion with a lot nobody seems really to know what the correct way of using it.

I add a quote from Brian Egan:

&gt; Yes, I see it as a way to propagate data down the tree. What I find
&gt; confusing, from the API docs:
&gt; 
&gt; &quot;Inherited widgets, when referenced in this way, will cause the
&gt; consumer to rebuild when the inherited widget itself changes state.&quot;
&gt; 
&gt; When I first read this, I thought:
&gt; 
&gt; I could stuff some data in the InheritedWidget and mutate it later.
&gt; When that mutation happens, it will rebuild all the Widgets that
&gt; reference my InheritedWidget What I found:
&gt; 
&gt; In order to mutate the State of an InheritedWidget, you need to wrap
&gt; it in a StatefulWidget You then actually mutate the state of the
&gt; StatefulWidget and pass this data down to the InheritedWidget, which
&gt; hands the data down to all of it&#39;s children. However, in that case, it
&gt; seems to rebuild the entire tree underneath the StatefulWidget, not
&gt; just the Widgets that reference the InheritedWidget. Is that correct?
&gt; Or will it somehow know how to skip the Widgets that reference the
&gt; InheritedWidget if updateShouldNotify returns false?

Flutter: How to correctly use an Inherited Widget?

Is there a way to remove the drop shadow under the app bar (AppBar class) when using a Scaffold widget in Flutter?

Removing the drop shadow from a Scaffold AppBar in Flutter?

Let&#39;s say you have a parent widget that might have a variable size.

For example:

    var container = new Container(
       height: 200.0, // Imagine this might change
       width: 200.0, // Imagine this might change
       // Imagine content in this container will 
       // depend on the parent container
       child: new Container(), 
    );

And maybe you want to have the child of the parent container render something different based on the size that it&#39;s given. 

*Think of responsive design breakpoints, if the width is over X use this layout, if the width is under X use that layout.*

What&#39;s the best way to do this in Flutter?

How can I layout widgets based on the size of the parent?

I&#39;m trying to bottom-center a widget at the bottom of a Column, but it keeps aligning to the left.

    return new Column(
      new Stack(
        new Positioned(
          bottom: 0.0, 
          new Center(
            new Container(),
          ),
        ),
      ),
    ); 

The existence of the Positioned forces the Container to the left, instead of centering. Removing the Positioned, however, puts the Container in the middle-center.

Flutter: Trying to bottom-center an item in a Column, but it keeps left-aligning

I want to have a row of IconButtons, all next to each other, but there seems to be pretty big padding between the actual icon, and the IconButton limits. I&#39;ve already set the padding on the button to 0.

This is my component, pretty straightforward:


    class ActionButtons extends StatelessWidget {
      @override
        Widget build(BuildContext context) {
          return Container(
            color: Colors.lightBlue,
            margin: const EdgeInsets.all(0.0),
            padding: const EdgeInsets.all(0.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.start,
              children: &lt;Widget&gt;[
                IconButton(
                  icon: new Icon(ScanrIcons.reg),
                  alignment: Alignment.center,
                  padding: new EdgeInsets.all(0.0),
                  onPressed: () {},
                ),
                IconButton(
                  icon: new Icon(Icons.volume_up),
                  alignment: Alignment.center,
                  padding: new EdgeInsets.all(0.0),
                  onPressed: () {},
                )
              ],
            ),
          );
        }
    }


[![enter image description here][1]][1]

I want to get rid of most of the light blue space, have my icons start earlier on the left, and closer to each other, but I can&#39;t find the way to resize the IconButton itself.

I&#39;m almost sure this space is taken by the button itself, &#39;cause if I change their alignments to `centerRight` and `centerLeft` they look like this:

[![enter image description here][2]][2]

Making the actual icons smaller doesn&#39;t help either, the button is still big:

[![enter image description here][3]][3]

thanks for the help


  [1]: https://i.stack.imgur.com/aQwXv.png
  [2]: https://i.stack.imgur.com/cT4s7.png
  [3]: https://i.stack.imgur.com/nhKjv.png

How do I remove Flutter IconButton big padding?

I am new in Flutter and I am trying receive data with a Dialog.
When a click in textField the error of image2 appear...

![Layout&#39;s Image][2]
![Error&#39;s Image][1]

    show(BuildContext context){
    
        var dialog = Dialog(
          child: Container(
            margin: EdgeInsets.all(8.0),
            child: Form(
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: &lt;Widget&gt;[
                  TextFormField(
                    decoration: InputDecoration(
                        labelText: &quot;Insira o n&#250;mero de telefone&quot;,
                        border: OutlineInputBorder(
                            borderRadius: BorderRadius.all(Radius.circular(2.0)))),
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.end,
                    children: &lt;Widget&gt;[
                      FlatButton(
                          onPressed: () {
                            Navigator.of(context).pop();
                          },
                          child: Text(&quot;Cancelar&quot;)),
                      FlatButton(
                          onPressed: () {
                            Navigator.of(context).pop();
                          },
                          child: Text(&quot;Aceitar&quot;))
                    ],
                  )
                ],
              ),
            ),
          ),
        );
    
        showDialog(context: context,builder: (context){
          return dialog;
        });
      }


This is my code.

    I/flutter (31032): Looking up a deactivated widget&#39;s ancestor is unsafe.
    I/flutter (31032): At this point the state of the widget&#39;s element tree is no longer stable. To safely refer to a
    I/flutter (31032): widget&#39;s ancestor in its dispose() method, save a reference to the ancestor by calling
    I/flutter (31032): inheritFromWidgetOfExactType() in the widget&#39;s didChangeDependencies() method.
    I/flutter (31032): 


  [1]: https://i.stack.imgur.com/Wlmmy.png
  [2]: https://i.stack.imgur.com/kWit6.png

Looking up a deactivated widget&#39;s ancestor is unsafe

Is there any way to show the scroll indicator on the `ListView`? 

Here is my basic code:

    ListView.builder(
      itemCount: 50,
      itemBuilder: (context, index) =&gt; ListTile(title: Text(&quot;Item= ${index + 1}&quot;),),
    )

How to add scroll indicator in ListView

I am facing a problem with the default padding of the widgets (IconButton, CheckBox, FlatButton). I have searched a lot for this concern but with no success. 

[![enter image description here][1]][1]

In the above image, the outer blue rect is the actual size of these widgets and I have to remove that space. 

    Checkbox(
              onChanged: (value) {
                setState(() {
                  _rememberMeFlag = !_rememberMeFlag;
                });
              },
              value: _rememberMeFlag,
              activeColor: const Color(0xff00bbff),
              materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
            )

and below is the widget code for hide/show widget icon:

    new Container(
              child: TextFormField(
                decoration: InputDecoration(
                  labelText: &quot;Password&quot;,
                  suffixIcon: Padding(
                    padding: EdgeInsetsDirectional.zero,
                    child: GestureDetector(
                      child: Icon(
                        hidePassword ? Icons.visibility : Icons.visibility_off,
                        size: 20.0,
                        color: Colors.black,
                      ),
                    ),
                  ),
                  contentPadding: const EdgeInsets.only(
                      left: 0.0, top: 6.0, bottom: 6.0, right: 0.0),
                ),
                obscureText: !hidePassword,
                maxLength: 20,
              ),
            )

I have tried to set the container size too but no luck. Also tried the padding properties of the widgets but with no success.

Is there any way to remove this extra spacing from these widgets?


  [1]: https://i.stack.imgur.com/AhOTU.png

All Flutter Widget Solutions on Gang of Coders

Total of 18 Flutter Widget Solutions