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flutter_docs

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appBar: AppBar(
title: text(title),
),
body: FutureBuilder<List<Photo>>(
future: fetchPhotos(http.Client()),
builder: (context, snapshot) {
if (snapshot.haserror) {
return const center(
child: Text('An error has occurred!'),
);
} else if (snapshot.hasdata) {
return PhotosList(photos: snapshot.data!);
} else {
return const center(
child: CircularProgressIndicator(),
);
}
},
),
);
}
}
class PhotosList extends StatelessWidget {
const PhotosList({super.key, required this.photos});
final List<Photo> photos;
@override
widget build(BuildContext context) {
return GridView.builder(
gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
crossAxisCount: 2,
),
itemCount: photos.length,
itemBuilder: (context, index) {
return Image.network(photos[index].thumbnailUrl);
},
);
}
}
<code_end>
<topic_end>
<topic_start>
persistence
<topic_end>
<topic_start>
topics
<topic_end>
<topic_start>
store key-value data on disk
if you have a relatively small collection of key-values
to save, you can use the shared_preferences plugin.
normally, you would have to
write native platform integrations for storing data on each platform.
fortunately, the shared_preferences plugin can be used to
persist key-value data to disk on each platform flutter supports.
this recipe uses the following steps:
info note
to learn more, watch this short package of the week video
on the shared_preferences package:
<topic_end>
<topic_start>
1. add the dependency
before starting, add the shared_preferences package as a dependency.
to add the shared_preferences package as a dependency,
run flutter pub add:
<topic_end>
<topic_start>
2. save data
to persist data, use the setter methods provided by the
SharedPreferences class. setter methods are available for
various primitive types, such as setInt, setBool, and setString.
setter methods do two things: first, synchronously update the
key-value pair in memory. then, persist the data to disk.
<code_start>
// load and obtain the shared preferences for this app.
final prefs = await SharedPreferences.getInstance();
// save the counter value to persistent storage under the 'counter' key.
await prefs.setInt('counter', counter);
<code_end>
<topic_end>
<topic_start>
3. read data
to read data, use the appropriate getter method provided by the
SharedPreferences class. for each setter there is a corresponding getter.
for example, you can use the getInt, getBool, and getString methods.
<code_start>
final prefs = await SharedPreferences.getInstance();
// try reading the counter value from persistent storage.
// if not present, null is returned, so default to 0.
final counter = prefs.getInt('counter') ?? 0;
<code_end>
note that the getter methods throw an exception if the persisted value
has a different type than the getter method expects.
<topic_end>
<topic_start>
4. remove data
to delete data, use the remove() method.
<code_start>
final prefs = await SharedPreferences.getInstance();
// remove the counter key-value pair from persistent storage.
await prefs.remove('counter');