List class - dart:core library (original) (raw)

An indexable collection of objects with a length.

Subclasses of this class implement different kinds of lists. The most common kinds of lists are:

• Fixed-length list
  An error occurs when attempting to use operations that can change the length of the list.
• Growable list
  Full implementation of the API defined in this class.

The default growable list, as created by [], keeps an internal buffer, and grows that buffer when necessary. This guarantees that a sequence of add operations will each execute in amortized constant time. Setting the length directly may take time proportional to the new length, and may change the internal capacity so that a following add operation will need to immediately increase the buffer capacity. Other list implementations may have different performance behavior.

Example of fixed-length list:

final fixedLengthList = List<int>.filled(5, 0); // Creates fixed-length list.
print(fixedLengthList); // [0, 0, 0, 0, 0]
fixedLengthList[0] = 87;
fixedLengthList.setAll(1, [1, 2, 3]);
print(fixedLengthList); // [87, 1, 2, 3, 0]
// Fixed length list length can't be changed or increased
fixedLengthList.length = 0;  // Throws
fixedLengthList.add(499);    // Throws

Example of growable list:

final growableList = <String>['A', 'B']; // Creates growable list.

To add data to the growable list, use operator[]=, add or addAll.

growableList[0] = 'G';
print(growableList); // [G, B]
growableList.add('X');
growableList.addAll({'C', 'B'});
print(growableList); // [G, B, X, C, B]

To check whether, and where, the element is in the list, use indexOf orlastIndexOf.

final indexA = growableList.indexOf('A'); // -1 (not in the list)
final firstIndexB = growableList.indexOf('B'); // 1
final lastIndexB = growableList.lastIndexOf('B'); // 4

To remove an element from the growable list, use remove, removeAt,removeLast, removeRange or removeWhere.

growableList.remove('C');
growableList.removeLast();
print(growableList); // [G, B, X]

To insert an element at position in the list, use insert or insertAll.

growableList.insert(1, 'New');
print(growableList); // [G, New, B, X]

To replace a range of elements in the list, use fillRange, replaceRangeor setRange.

growableList.replaceRange(0, 2, ['AB', 'A']);
print(growableList); // [AB, A, B, X]
growableList.fillRange(2, 4, 'F');
print(growableList); // [AB, A, F, F]

To sort the elements of the list, use sort.

growableList.sort((a, b) => a.compareTo(b));
print(growableList); // [A, AB, F, F]

To shuffle the elements of this list randomly, use shuffle.

growableList.shuffle();
print(growableList); // e.g. [AB, F, A, F]

To find the first element satisfying some predicate, or give a default value if none do, use firstWhere.

bool isVowel(String char) => char.length == 1 && "AEIOU".contains(char);
final firstVowel = growableList.firstWhere(isVowel, orElse: () => ''); // ''

There are similar lastWhere and singleWhere methods.

A list is an Iterable and supports all its methods, includingwhere, map, whereType and toList.

Lists are Iterable. Iteration occurs over values in index order. Changing the values does not affect iteration, but changing the valid indices—that is, changing the list's length—between iteration steps causes a ConcurrentModificationError. This means that only growable lists can throw ConcurrentModificationError. If the length changes temporarily and is restored before continuing the iteration, the iterator might not detect it.

It is generally not allowed to modify the list's length (adding or removing elements) while an operation on the list is being performed, for example during a call to forEach or sort. Changing the list's length while it is being iterated, either by iterating it directly or through iterating an Iterable that is backed by the list, will break the iteration.

Implemented types

• Iterable<E>

Implementers

• DomRectList
• DomStringList
• FileList
• HtmlCollection
• ImmutableListMixin
• LengthList
• ListBase
• MimeTypeArray
• NodeList
• NumberList
• PluginArray
• SourceBufferList
• SpeechGrammarList
• StringList
• TextTrackCueList
• TextTrackList
• TouchList
• TransformList
• TypedDataList
• UnmodifiableListView

Available extensions

• EnumByName
• FutureIterable
• IterableExtensions
• ListToJSArray
• NullableIterableExtensions

Constructors

List.empty({bool growable = false})

Creates a new empty list.

factory

List.filled(int length, E fill, {bool growable = false})

Creates a list of the given length with fill at each position.

factory

List.from(Iterable elements, {bool growable = true})

Creates a list containing all elements.

factory

List.generate(int length, E generator(int index), {bool growable = true})

Generates a list of values.

factory

List.of(Iterable<E> elements, {bool growable = true})

Creates a list from elements.

factory

List.unmodifiable(Iterable elements)

Creates an unmodifiable list containing all elements.

factory

Properties

first ↔ E

The first element.

getter/setter pairinherited-getter

firstOrNull → T?

Available on Iterable<T>, provided by the IterableExtensions extension

The first element of this iterator, or null if the iterable is empty.

no setter

hashCode → int

The hash code for this object.

no setterinherited

indexed → Iterable<(int, T)>

Available on Iterable<T>, provided by the IterableExtensions extension

Pairs of elements of the indices and elements of this iterable.

no setter

isEmpty → bool

Whether this collection has no elements.

no setterinherited

isNotEmpty → bool

Whether this collection has at least one element.

no setterinherited

iterator → Iterator<E>

A new Iterator that allows iterating the elements of this Iterable.

no setterinherited

last ↔ E

The last element.

getter/setter pairinherited-getter

lastOrNull → T?

Available on Iterable<T>, provided by the IterableExtensions extension

The last element of this iterable, or null if the iterable is empty.

no setter

length ↔ int

The number of objects in this list.

getter/setter pairoverride-getter

nonNulls → Iterable<T>

Available on Iterable<T?>, provided by the NullableIterableExtensions extension

The non-null elements of this iterable.

no setter

reversed → Iterable<E>

An Iterable of the objects in this list in reverse order.

no setter

runtimeType → Type

A representation of the runtime type of the object.

no setterinherited

single → E

Checks that this iterable has only one element, and returns that element.

no setterinherited

singleOrNull → T?

Available on Iterable<T>, provided by the IterableExtensions extension

The single element of this iterator, or null.

no setter

toJS → JSArray<T>

Available on List<T>, provided by the ListToJSArray extension

Converts this List to a JSArray by either casting, unwrapping, or cloning the List.

no setter

toJSProxyOrRef → JSArray<T>

Available on List<T>, provided by the ListToJSArray extension

Converts this List to a JSArray by either casting, unwrapping, or proxying the List.

no setter

wait → Future<List<T>>

Available on Iterable<Future<T>>, provided by the FutureIterable extension

Waits for futures in parallel.

no setter

Methods

add(E value)→ void

Adds value to the end of this list, extending the length by one.

addAll(Iterable<E> iterable)→ void

Appends all objects of iterable to the end of this list.

any(bool test(E element))→ bool

Checks whether any element of this iterable satisfies test.

inherited

asMap()→ Map<int, E>

An unmodifiable Map view of this list.

asNameMap()→ Map<String, T>

Available on Iterable<T>, provided by the EnumByName extension

Creates a map from the names of enum values to the values.

byName(String name)→ T

Available on Iterable<T>, provided by the EnumByName extension

Finds the enum value in this list with name name.

cast<R>()→ List<R>

Returns a view of this list as a list of R instances.

override

clear()→ void

Removes all objects from this list; the length of the list becomes zero.

contains(Object? element)→ bool

Whether the collection contains an element equal to element.

inherited

elementAt(int index)→ E

Returns the indexth element.

inherited

elementAtOrNull(int index)→ T?

Available on Iterable<T>, provided by the IterableExtensions extension

The element at position index of this iterable, or null.

every(bool test(E element))→ bool

Checks whether every element of this iterable satisfies test.

inherited

expand<T>(Iterable<T> toElements(E element))→ Iterable<T>

Expands each element of this Iterable into zero or more elements.

inherited

fillRange(int start, int end, [E? fillValue])→ void

Overwrites a range of elements with fillValue.

firstWhere(bool test(E element), {E orElse()?})→ E

The first element that satisfies the given predicate test.

inherited

fold<T>(T initialValue, T combine(T previousValue, E element))→ T

Reduces a collection to a single value by iteratively combining each element of the collection with an existing value

inherited

followedBy(Iterable<E> other)→ Iterable<E>

Creates the lazy concatenation of this iterable and other.

inherited

forEach(void action(E element))→ void

Invokes action on each element of this iterable in iteration order.

inherited

getRange(int start, int end)→ Iterable<E>

Creates an Iterable that iterates over a range of elements.

indexOf(E element, [int start = 0])→ int

The first index of element in this list.

indexWhere(bool test(E element), [int start = 0])→ int

The first index in the list that satisfies the provided test.

insert(int index, E element)→ void

Inserts element at position index in this list.

insertAll(int index, Iterable<E> iterable)→ void

Inserts all objects of iterable at position index in this list.

join([String separator = ""])→ String

Converts each element to a String and concatenates the strings.

inherited

lastIndexOf(E element, [int? start])→ int

The last index of element in this list.

lastIndexWhere(bool test(E element), [int? start])→ int

The last index in the list that satisfies the provided test.

lastWhere(bool test(E element), {E orElse()?})→ E

The last element that satisfies the given predicate test.

inherited

map<T>(T toElement(E e))→ Iterable<T>

The current elements of this iterable modified by toElement.

inherited

noSuchMethod(Invocation invocation)→ dynamic

Invoked when a nonexistent method or property is accessed.

inherited

reduce(E combine(E value, E element))→ E

Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.

inherited

remove(Object? value)→ bool

Removes the first occurrence of value from this list.

removeAt(int index)→ E

Removes the object at position index from this list.

removeLast()→ E

Removes and returns the last object in this list.

removeRange(int start, int end)→ void

Removes a range of elements from the list.

removeWhere(bool test(E element))→ void

Removes all objects from this list that satisfy test.

replaceRange(int start, int end, Iterable<E> replacements)→ void

Replaces a range of elements with the elements of replacements.

retainWhere(bool test(E element))→ void

Removes all objects from this list that fail to satisfy test.

setAll(int index, Iterable<E> iterable)→ void

Overwrites elements with the objects of iterable.

setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0])→ void

Writes some elements of iterable into a range of this list.

shuffle([Random? random])→ void

Shuffles the elements of this list randomly.

singleWhere(bool test(E element), {E orElse()?})→ E

The single element that satisfies test.

inherited

skip(int count)→ Iterable<E>

Creates an Iterable that provides all but the first count elements.

inherited

skipWhile(bool test(E value))→ Iterable<E>

Creates an Iterable that skips leading elements while test is satisfied.

inherited

sort([int compare(E a, E b)?])→ void

Sorts this list according to the order specified by the compare function.

sublist(int start, [int? end])→ List<E>

Returns a new list containing the elements between start and end.

take(int count)→ Iterable<E>

Creates a lazy iterable of the count first elements of this iterable.

inherited

takeWhile(bool test(E value))→ Iterable<E>

Creates a lazy iterable of the leading elements satisfying test.

inherited

toList({bool growable = true})→ List<E>

Creates a List containing the elements of this Iterable.

inherited

toSet()→ Set<E>

Creates a Set containing the same elements as this iterable.

inherited

toString()→ String

A string representation of this object.

inherited

where(bool test(E element))→ Iterable<E>

Creates a new lazy Iterable with all elements that satisfy the predicate test.

inherited

whereType<T>()→ Iterable<T>

Creates a new lazy Iterable with all elements that have type T.

inherited

Operators

operator +(List<E> other)→ List<E>

Returns the concatenation of this list and other.

operator ==(Object other)→ bool

Whether this list is equal to other.

override

operator [](int index)→ E

The object at the given index in the list.

operator []=(int index, E value)→ void

Sets the value at the given index in the list to value.

Static Methods

castFrom<S, T>(List<S> source)→ List<T>

Adapts source to be a List<T>.

override

copyRange<T>(List<T> target, int at, List<T> source, [int? start, int? end])→ void

Copy a range of one list into another list.

writeIterable<T>(List<T> target, int at, Iterable<T> source)→ void

Write the elements of an iterable into a list.