How to set margin for a Button in Flutter

I am just creating a form in Flutter. I am not able to set the top margin for the button.

class _MyHomePageState extends State<MyHomePage> {
  
String firstname; 
String lastname;
final scaffoldKey = new GlobalKey<ScaffoldState>();
final formKey = new GlobalKey<FormState>();


    @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: scaffoldKey,
      appBar: new AppBar(
        title: new Text('Validating forms'),
      ),
      body: new Padding(
        padding: const EdgeInsets.all(16.0),
        child: new Form(
          key: formKey,
          child: new Column(
            children: [
              new TextFormField(
                decoration: new InputDecoration(labelText: 'First Name'),
                validator: (val) =>
                    val.length == 0 ?"Enter FirstName" : null,
                onSaved: (val) => firstname = val,
              ),
              new TextFormField(
                decoration: new InputDecoration(labelText: 'Password'),
                validator: (val) =>
                    val.length ==0 ? 'Enter LastName' : null,
                onSaved: (val) => lastname = val,
                obscureText: true,
              ),
              new RaisedButton(
                onPressed: _submit,
                child: new Text('Login'),
              ),
            ],
          ),
        ),
      ),
    );
  }

Put your button inside a Container and then set the margin

new Container(
    margin: const EdgeInsets.only(top: 10.0),
    child : new RaisedButton(
                onPressed: _submit,
                child: new Text('Login'),
              ),

Alternatively you can wrap your button with Padding. (That is what Container does internally.)

Padding(
  padding: const EdgeInsets.all(20),
  child: ElevatedButton(
    onPressed: _submit,
    child: Text('Login'),
  ),
);

See this answer more more on adding margin to a widget.

Note: RaisedButton is deprecated as of Flutter 2.0. ElevatedButton is the replacement.

In Flutter 2.0, RaisedButton was deprecated, The ElevatedButton is replacement.
So you can use ElevatedButton and set style as bellow to remove margin:

      ElevatedButton.icon(
        onPressed: () {},
        icon: Icon(Icons.add),
        label: Text(
          'Add Place',
        ),
        style: ButtonStyle(tapTargetSize: MaterialTapTargetSize.shrinkWrap),
      ),

image marging top:

        Scaffold(
      backgroundColor: Color.fromARGB(255, 238, 237, 237),
      body: Center(
        child: Container(
          margin: const EdgeInsets.only(top: 25),
          child: Column(
            children: <Widget>[
              Column(children: <Widget>[
                Image.asset(
                  'images/logo.png',
                  fit: BoxFit.contain,
                  width: 130,
                )
              ]),
              
            ],
          ),
        ),
      ),
    )

I found the EdgeInsets.symmetric:

child : new RaisedButton(
   onPressed: _submit,
   child: new Text('Login'),
   padding: EdgeInsets.symmetric(horizontal: 50, vertical: 10),
),

Screenshot:

Use the recommended ElevatedButton.style property to provide padding.

ElevatedButton(
  onPressed: () {},
  child: Text('Button'),
  style: ElevatedButton.styleFrom(
    padding: EdgeInsets.all(20), // Set padding
  ),
)

This is how I set the size, padding, and margin of widgets in general. here is an example for Button:

   Container(
          margin: EdgeInsets.only(top: 10), // Top Margin
          child:
            ElevatedButton(
              style: TextButton.styleFrom(

                // Inside Padding 
                padding: EdgeInsets.symmetric(horizontal: 0, vertical: 20), 

                // Width,Height
                minimumSize: Size(300, 30), 
              ),
              child: Text('Upload Data'),
              onPressed: () {submitForm();},
            ),
        ),

Other Options are

Container(
          margin: EdgeInsets.only(top:20),
          child:
            ElevatedButton(

set horizontal & vertical margins

Container(
margin: EdgeInsets.symmetric(horizontal: 0, vertical: 20),
child:

Container(
          margin: EdgeInsets.all(20),
          child:
            ElevatedButton(

Container(
          margin: EdgeInsets.fromLTRB(5,10,5,10),
          child:
            ElevatedButton(

child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              Text(data.dataList[index].codeName, style: TextStyle(fontSize: 14, fontWeight: FontWeight.w500, color: UtilColors.darkGrey)),
              Row(
                //TODO to edit employee details
                crossAxisAlignment: CrossAxisAlignment.end,
                children: <Widget>[
                  Expanded(child: Text(BasicAction.formatDate(data.dataList[index].payDate), style: TextStyle(fontSize: 16, fontWeight: FontWeight.w500, color: UtilColors.darkGrey))),
                  Padding(
                    padding: EdgeInsets.all(4),
                    child: Text('Edit', style: TextStyle(fontSize: 14, fontWeight: FontWeight.w500, color: UtilColors.blueColor)),
                  ),
                ],
              ),
            ],
          ),

in this on edit text how to set clicklistenr 

You can use margin and padding on Card like this:-

 @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: ListView.builder(
          itemCount: _newsArticles.length,
          padding:  EdgeInsets.symmetric(horizontal: 2,vertical: 2),
          itemBuilder: (context, index) {
            return Card( // <-- Card widget
              shadowColor: Colors.grey,
              elevation: 3,
              margin: EdgeInsets.all(5.0),
              child: ListTile(
                title: _newsArticles[index].urlToImage == null ?
                Image.asset(Constants.NEWS_PLACEHOLDER_IMAGE_ASSET_URL) :
                Image.network(_newsArticles[index].urlToImage),
                subtitle: Text(_newsArticles[index].title, style: TextStyle(fontSize: 14)),
              ),
            );
          },
        )
    );
  }