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

问题

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,
  ],
);

回答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),
  ),
),

回答2:

The following will fit the image to 100% of container width while the height is constant. For local assets, use AssetImage

Container(
  width: MediaQuery.of(context).size.width,
  height: 100,
  decoration: BoxDecoration(
    image: DecorationImage(
      fit: BoxFit.fill,
      image: NetworkImage("https://picsum.photos/250?image=9"),
    ),
  ),
)

Image fill modes:

Fill - Image is stretched
```
fit: BoxFit.fill
```
Fit Height - image kept proportional while making sure the full height of the image is shown (may overflow)
```
fit: BoxFit.fitHeight
```
Fit Width - image kept proportional while making sure the full width of the image is shown (may overflow)
```
fit: BoxFit.fitWidth
```
Cover - image kept proportional, ensures maximum coverage of the container (may overflow)
```
fit: BoxFit.cover
```
Contain - image kept proportional, minimal as possible, will reduce it's size if needed to display the entire image
```
fit: BoxFit.contain
```

回答3:

Inside your Stack, you should wrap your background widget in a Positioned.fill.

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

回答4:

I think that for your purpose Flex could work better than Container():

new Flex(
    direction: Axis.vertical,
    children: <Widget>[
      Image.asset(asset.background)
    ],
   )

回答5:

For filling, I sometimes use SizedBox.expand

回答6:

Try setting contentPadding

ListTile(
  contentPadding: EdgeInsets.all(0.0),
  ...
)

回答7:

Your Question contains the first step, but you need width and height. you can get the width and height of the screen. Here is a small edit

//gets the screen width and height
double Width = MediaQuery.of(context).size.width;
double Height = MediaQuery.of(context).size.height;

Widget background = new Image.asset(
  asset.background,
  fit: BoxFit.fill,
  width: Width,
  height: Height,
);

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

You can also use Width and Height to size other objects based on screen size.

ex: width: Height/2, height: Height/2 //using height for both keeps aspect ratio

来源：https://stackoverflow.com/questions/45745448/how-do-i-stretch-an-image-to-fit-the-whole-background-100-height-x-100-width

标签

image

containers

Flutter

stretch