Future.wait
- Dart course
- Intermediate
- Lesson 61/116
- 5 min
Learn parallel Futures with Future.wait.
Future.wait
Future.wait runs multiple Futures in parallel and waits for all of them. The result is a list containing the results of each Future.
Example: var results = await Future.wait([Future.value('A'), Future.value('B'), Future.value('C')]);. Three Futures start in parallel; await waits for all. results is a List: ['A', 'B', 'C'].
This method speeds up independent operations. If three network requests each take 1 second, running them in parallel takes 1 second total.
Parallel execution
Future.wait starts all Futures in the list at the same time. Each completes independently; Future.wait waits until all are done. The result list is ordered by the Future order.
Example: three Futures take 3, 1 and 2 seconds. With Future.wait they all start in parallel; total time is the longest, 3 seconds. Sequentially it would take 6 seconds.
In the result list each Future's result sits at its own index. results[0] gives the first Future's result.
Practice Wait for three Futures in parallel
void main() async is already written. Pass three Future.value ('A', 'B', 'C') to Future.wait. Wait with await and print the result with print.
Starter code
void main() async {
// run three Futures in parallel with Future.wait
// wait and print the result
}Sample solution
void main() async {
var results = await Future.wait([
Future.value('A'),
Future.value('B'),
Future.value('C'),
]);
print(results);
}Expected output
[A, B, C]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does Future.wait return?
var r = await Future.wait([
Future.value('A'),
Future.value('B'),
]);- A list of results Correct answer
- void
- It throws
- A single value
Explanation: Future.wait returns a list containing the result of each Future.
2 The Future.wait call
var results = await ____([Future.value('A'), Future.value('B'), Future.value('C')]);var results = await Future.wait([Future.value('A'), Future.value('B'), Future.value('C')]);Explanation: Future.wait waits for parallel Futures.
3 Match the Future.wait parts
| Term | Meaning |
|---|---|
Future.wait([...]) |
Parallel wait |
await |
Wait for completion |
results |
Result list |
results[0] |
First result |