dart-sdk/samples-dev/swarm/BiIterator.dart
Leaf Petersen 745f112ef6 Opt out some files from null safety.
Opt an initial batch of files under samples, samples-dev,
utils, and runtime/tools/dartfuzz out of null safety in preparation
for switching the flag on by default.

Change-Id: Icdfd52a5a969e678a7205903332f73fe3841c223
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/166960
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Leaf Petersen <leafp@google.com>
2020-10-12 22:15:42 +00:00

71 lines
1.6 KiB
Dart

// @dart = 2.9
part of swarmlib;
/**
* An iterator that allows the user to move forward and backward though
* a set of items. (Bi-directional)
*/
class BiIterator<E> {
/**
* Provides forward and backward iterator functionality to keep track
* which item is currently selected.
*/
ObservableValue<int> currentIndex;
/**
* The collection of items we will be iterating through.
*/
List<E> list;
BiIterator(this.list, [List<ChangeListener> oldListeners = null])
: currentIndex = new ObservableValue<int>(0) {
if (oldListeners != null) {
currentIndex.listeners = oldListeners;
}
}
/**
* Returns the next section from the sections, given the current
* position. Returns the last source if there is no next section.
*/
E next() {
if (currentIndex.value < list.length - 1) {
currentIndex.value += 1;
}
return list[currentIndex.value];
}
/**
* Returns the current Section (page in the UI) that the user is
* looking at.
*/
E get current {
return list[currentIndex.value];
}
/**
* Returns the previous section from the sections, given the current
* position. Returns the front section if we are already at the front of
* the list.
*/
E previous() {
if (currentIndex.value > 0) {
currentIndex.value -= 1;
}
return list[currentIndex.value];
}
/**
* Move the iterator pointer over so that it points to a given list item.
*/
void jumpToValue(E val) {
for (int i = 0; i < list.length; i++) {
if (identical(list[i], val)) {
currentIndex.value = i;
break;
}
}
}
}