How do I stretch an image to fit the whole background (100% height x 100% width) in Flutter?

Question

I have an image that doesn't match the aspect ratio of my device's screen. I want to stretch the image so that it fully fills the screen, and I don't want to crop any part of the image.

CSS has the concept of percentages, so I could just set height and width to 100%. But it doesn't seem like Flutter has that concept, and it's bad to just hard code the height and width, so I'm stuck.

Here's what I have (I'm using a Stack since I have something in the foreground of the image):

Widget background = new Container(
  height: // Not sure what to put here!
  width: // Not sure what to put here!
  child: new Image.asset(
    asset.background,
    fit: BoxFit.fill, // I thought this would fill up my Container but it doesn't
  ),
);

return new Stack(
  children: <Widget>[
    background,
    foreground,
  ],
);

Answer 1

To make an Image fill its parent, simply wrap it into a FittedBox:

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

FittedBox here will stretch the image to fill the space. (Note that this functionality used to be provided by BoxFit.fill, but the API has meanwhile changed such that BoxFit no longer provides this functionality. FittedBox should work as a drop-in replacement, no changes need to be made to the constructor arguments.)

---

Alternatively, for complex decorations you can use a Container instead of an Image – and use decoration/foregroundDecoration fields.

To make the Container will its parent, it should either:

• have no child
• have alignment property not null

Here's an example that combines two images and a Text in a single Container, while taking 100% width/height of its parent:

Container(
  foregroundDecoration: const BoxDecoration(
    image: DecorationImage(
        image: NetworkImage(
            'https://p6.storage.canalblog.com/69/50/922142/85510911_o.png'),
        fit: BoxFit.fill),
  ),
  decoration: const BoxDecoration(
    image: DecorationImage(
        alignment: Alignment(-.2, 0),
        image: NetworkImage(
            'http://www.naturerights.com/blog/wp-content/uploads/2017/12/Taranaki-NR-post-1170x550.png'),
        fit: BoxFit.cover),
  ),
  alignment: Alignment.bottomCenter,
  padding: EdgeInsets.only(bottom: 20),
  child: Text(
    "Hello World",
    style: Theme.of(context)
        .textTheme
        .display1
        .copyWith(color: Colors.white),
  ),
),