How to remove extra padding around AppBar leading icon in Flutter

问题

In my Flutter app, I have this AppBar

Widget setAppBar(){
  return new AppBar(
    title: addAppBarTextWidget('Explore'),
    elevation: 0.0,
    leading: addLeadingIcon(),
    actions: <Widget>[
      addAppBarActionWidget(Constant.iconNotification, 22.0, 16.0, 8.0),
      addAppBarActionWidget(Constant.iconProfile, 30.0, 30.0, 15.0)
    ],
  );
}

Widget addLeadingIcon(){
  return new Container(
    height: 25.0,
    width: 25.0,
    padding: const EdgeInsets.fromLTRB(0.0, 0.0, 0.0, 0.0),
    margin: const EdgeInsets.fromLTRB(0.0, 0.0, 0.0, 0.0),
    child: new Stack(
      alignment: AlignmentDirectional.center,
      children: <Widget>[
        new Image.asset(
          Constant.iconNotification,
          width: 25.0,
          height: 25.0,
        ),
        new FlatButton(
            onPressed: (){
              onLeadingShowCategoryClick();
            }
        )
      ],
    ),
  );
}

it looks like:

As you can see on the AppBar, there is some extra padding around the leading icon. How can I remove this extra padding.

回答1:

You can't do this because it is a predefined widget. You can, however, do this:

appBar: AppBar(
  automaticallyImplyLeading: false, // Don't show the leading button
  title: Row(
    mainAxisAlignment: MainAxisAlignment.start,
    crossAxisAlignment: CrossAxisAlignment.center,
    children: <Widget>[
      IconButton(
        onPressed: () => Navigator.pop(context),
        icon: Icon(Icons.arrow_back, color: Colors.white),
      ),
      // Your widgets here
    ],
  ),
),

Where automaticallyImplyLeading: true hides the leading IconButton so you can add your own widgets.

回答2:

Just add a property called titleSpacing,

Sample

appBar: new AppBar(
        leading: new Icon(Icons.android),
        titleSpacing: 0.0,
        title: new Text(widget.title),
      ),

回答3:

If you use Widgets from Material package, they are defined respecting Material Design specification document. So if your modification violates this spec, you have to build your own Widget instead of using the Material Widgets.

回答4:

Complete working workaround with some input from Adrian.

return Scaffold(
  key: _scaffoldKey,
  appBar: AppBar(
    titleSpacing: 0.0,
    title: Row(
      mainAxisAlignment: MainAxisAlignment.start,
      crossAxisAlignment: CrossAxisAlignment.center,
      children: <Widget>[
        IconButton(
          icon: Icon(Icons.menu),
          onPressed: () => _scaffoldKey.currentState.openDrawer(),
        ),
        Stack(
          alignment: Alignment.center,
          children: <Widget>[
            IconButton(
              icon: Icon(Icons.mail_outline),
              onPressed: _onClickNotification,
            ),
            Positioned(
              top: 12.0,
              right: 10.0,
              width: 10.0,
              height: 10.0,
              child: Container(
                decoration: BoxDecoration(
                  shape: BoxShape.circle,
                  color: AppColors.notification,
                ),
              ),
            )
          ],
        ),
        Expanded(
          child: Center(child: Text('test')),
        )
      ],
    ),
    automaticallyImplyLeading: false,
    centerTitle: true,
    actions: <Widget>[
      Row(
        children: <Widget>[
          Text('Online'),
          Switch(
            value: true,
            onChanged: (bool value) {},
          )
        ],
      )
    ],
  ),
  drawer: Drawer(
    child: _buildDrawer(),
  ),
  body: Container(
    color: Colors.orange,
  ),
);

回答5:

If you just need to move the icon a bit to the left like I did, you can still use the leading property and just set the alignment on the IconButton:

    leading: Builder(
      builder: (BuildContext context) {
        return IconButton(
          onPressed: () => Navigator.pop(context),
          icon: MyIcon(),
          alignment: Alignment(-0.5, 0.0), // move icon a bit to the left
        );
      },
    ),

来源：https://stackoverflow.com/questions/50460629/how-to-remove-extra-padding-around-appbar-leading-icon-in-flutter