Implement swipe to dismiss

The “swipe to dismiss” pattern is common in many mobile apps. For example, when writing an email app, you might want to allow a user to swipe away email messages to delete them from a list.

Flutter makes this task easy by providing the Dismissible widget. Learn how to implement swipe to dismiss with the following steps:

  1. Create a list of items.
  2. Wrap each item in a Dismissible widget.
  3. Provide “leave behind” indicators.

1. Create a list of items

First, create a list of items. For detailed instructions on how to create a list, follow the Working with long lists recipe.

Create a data source

In this example, you want 20 sample items to work with. To keep it simple, generate a list of strings.

final items = List<String>.generate(20, (i) => "Item ${i + 1}");

Convert the data source into a list

Display each item in the list on screen. Users won’t be able to swipe these items away just yet.

ListView.builder(
  itemCount: items.length,
  itemBuilder: (context, index) {
    return ListTile(title: Text('${items[index]}'));
  },
);

2. Wrap each item in a Dismissible widget

In this step, give users the ability to swipe an item off the list by using the Dismissible widget.

After the user has swiped away the item, remove the item from the list and display a snackbar. In a real app, you might need to perform more complex logic, such as removing the item from a web service or database.

Update the itemBuilder() function to return a Dismissible widget:

Dismissible(
  // Each Dismissible must contain a Key. Keys allow Flutter to
  // uniquely identify widgets.
  key: Key(item),
  // Provide a function that tells the app
  // what to do after an item has been swiped away.
  onDismissed: (direction) {
    // Remove the item from the data source.
    setState(() {
      items.removeAt(index);
    });

    // Show a snackbar. This snackbar could also contain "Undo" actions.
    Scaffold
        .of(context)
        .showSnackBar(SnackBar(content: Text("$item dismissed")));
  },
  child: ListTile(title: Text('$item')),
);

3. Provide “leave behind” indicators

As it stands, the app allows users to swipe items off the list, but it doesn’t give a visual indication of what happens when they do. To provide a cue that items are removed, display a “leave behind” indicator as they swipe the item off the screen. In this case, the indicator is a red background.

To add the indicator, provide a background parameter to the Dismissible.

Dismissible(
  // Show a red background as the item is swiped away.
  background: Container(color: Colors.red),
  key: Key(item),
  onDismissed: (direction) {
    setState(() {
      items.removeAt(index);
    });

    Scaffold
        .of(context)
        .showSnackBar(SnackBar(content: Text("$item dismissed")));
  },
  child: ListTile(title: Text('$item')),
);

Complete example

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

// MyApp is a StatefulWidget. This allows updating the state of the
// widget when an item is removed.
class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);

  @override
  MyAppState createState() {
    return MyAppState();
  }
}

class MyAppState extends State<MyApp> {
  final items = List<String>.generate(3, (i) => "Item ${i + 1}");

  @override
  Widget build(BuildContext context) {
    final title = 'Dismissing Items';

    return MaterialApp(
      title: title,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: ListView.builder(
          itemCount: items.length,
          itemBuilder: (context, index) {
            final item = items[index];

            return Dismissible(
              // Each Dismissible must contain a Key. Keys allow Flutter to
              // uniquely identify widgets.
              key: Key(item),
              // Provide a function that tells the app
              // what to do after an item has been swiped away.
              onDismissed: (direction) {
                // Remove the item from the data source.
                setState(() {
                  items.removeAt(index);
                });

                // Then show a snackbar.
                Scaffold.of(context)
                    .showSnackBar(SnackBar(content: Text("$item dismissed")));
              },
              // Show a red background as the item is swiped away.
              background: Container(color: Colors.red),
              child: ListTile(title: Text('$item')),
            );
          },
        ),
      ),
    );
  }
}

Dismissible Demo