Following examples show how to create and manipulate with .NET strongly typed list List<T>.
List<T>
List is a generic type, so you can create list of any type (it can be reference type such as Customer or value type such as int)
var list1 = new List<object>();
var list2 = new List<Customer>();
var list3 = new List<int>();
All the following examples use list of integer values List<int>.
Creates an empty list (of integer values).
var list = new List<int>();
Creates a list and initializes it with some items (integer values).
var list = new List<int>() { 8, 3, 2 };
Creates a list and initializes it with items of another list (or array or anything which implements IEnumerable interface).
var listA = new List<int>() { 8, 3, 2 };
var listB = new List<int>(listA);
Creates a list with specified capacity.
var list = new List<int>(16);
| list.Count: | 0 |
|---|
| list.Capacity: | 16 |
|---|
Gets an item at the specified zero-based index.
Sets the item at the specified zero-based index.
Adds an item to the end of the list.
Adds items of another list (or an IEnumerable collection) to the end of the list.
Returns the zero-based index of the item in the sorted list. If the items is not found, returns a negative number. See MSDN for more info.
This List<T> method works only if the type T implements IComparable<T> or IComparable interface.
int index = list.BinarySearch(6);
This BinarySearch method overload uses specified comparer.
int index = list.BinarySearch( item: 6, comparer: new MyComparer() );
This BinarySearch method overload uses specified comparer and search in specified range.
int index = list.BinarySearch( index: 1, count: 3, item: 6, comparer: new MyComparer() );
This example shows the case when the item was not found in the list. The result is negative number.
int index = list.BinarySearch( index: 1, count: 2, item: 6, comparer: new MyComparer() );
public class MyComparer : IComparer<int>
{
public int Compare(int x, int y) { return x.CompareTo(y); }
}
Removes all items from the list. Count is zero, Capacity is unchanged.
Returns true if the list contains the specified item.
bool result = list.Contains(3);
Returns false if the list doesn't contain the specified item.
bool result = list.Contains(6);
Converts items using specified delegate. Items can be converted to another type.
var conv = new Converter<int, decimal>(x => (decimal)(x+1));
var listB = listA.ConvertAll<decimal>(conv);
Copies all list items into the beginning of the specified array.
| list: | 8 3 2 |
|---|
| array: | 0 0 0 0 0 |
|---|
list.CopyTo(array);
Copies all list items into the array, starting from the specified array index.
| list: | 8 3 2 |
|---|
| array: | 0 0 0 0 0 |
|---|
list.CopyTo(array, arrayIndex: 2);
Copies a range of list items into the array, starting from the specified array index.
| list: | 8 3 2 |
|---|
| array: | 0 0 0 0 0 |
|---|
list.CopyTo(index: 1, array: array, arrayIndex: 3, count: 1);
Returns true if the list contains items matching the specified predicate.
bool result = list.Exists(x => x == 3);
Returns false if the list doesn't contain items matching the specified predicate.
bool result = list.Exists(x => x > 10);
Returns true if the two specified lists are reference equal (are the same instance).
var listA = new List<int>() { 8, 3, 2 };
var listB = listA;
bool result = listA.Equals(listB);
Returns false if the specified two lists are not the same instance. To determine whether all items of the two lists are equal use LINQ method SequenceEqual.
var listA = new List<int>() { 8, 3, 2 };
var listB = new List<int>() { 8, 3, 2 };
bool result = listA.Equals(listB);
Returns the first occurrence of item matching the specified predicate.
int item = list.Find(x => x > 2);
For List<T> returns the default value of type T if no item matches the predicate. In this case the default value of int is 0.
int item = list.Find(x => x > 10);
Returns list with items matching the specified predicate.
var listB = listA.FindAll(x => x > 2);
Returns empty list, if no item matches the specified predicate.
var listB = listA.FindAll(x => x > 10);
Returns zero-based index of the first item which matches the specified predicate.
int index = list.FindIndex(x => x < 5);
Returns index of the first item which matches the specified predicate. It searches the list from startIndex to the end of the list.
int index = list.FindIndex( startIndex: 2, match: x => x < 5);
Returns index of the first item which matches the specified predicate. It searches the list in the range specified by startIndex and count.
int index = list.FindIndex( startIndex: 2, count: 2, match: x => x < 5);
Returns -1 if no item matches the specified predicate.
int index = list.FindIndex( startIndex: 2, count: 2, match: x => x < 3);
Returns the last occurrence of item matching the specified predicate.
int item = list.FindLast(x => x < 5);
For List<T> returns the default value of type T if no item matches the predicate. In this case the default value of int is 0.
int item = list.FindLast(x => x > 10);
Returns zero-based index of the last item which matches the specified predicate.
int index = list.FindLastIndex(x => x < 5);
Returns index of the last item which matches the specified predicate. It searches the list from the beginning to the specified startIndex.
int index = list.FindLastIndex( startIndex: 2, match: x => x < 5);
Returns index of the last item which matches the specified predicate in the range specified by count and the end index surprisingly called startIndex.
int index = list.FindLastIndex( startIndex: 2, count: 2, match: x => x < 5);
Returns -1 if no item matches the specified predicate.
int index = list.FindLastIndex( startIndex: 2, count: 2, match: x => x < 3);
Executes the specified action for each item in the list. It does the same as standard C# foreach statement.
list.ForEach(x => { Console.Write(x); });
Returns a list with a range of items of the source list.
var listB = listA.GetRange( index: 1, count: 3);
Returns the zero-based index of the first occurrence of the item in the list.
int index = list.IndexOf(8);
Returns the index of the first occurrence of the item in the list. It searches the list from the specified index to the end of the list.
int index = list.IndexOf(item: 8, index: 1);
Returns the index of the first occurrence of the item in the list. It searches the list in the range specified by index and count.
int index = list.IndexOf(item: 3, index: 1, count: 2);
Returns -1 if the item is not found in the specified range.
int index = list.IndexOf(item: 8, index: 1, count: 2);
Inserts an item into the list at the specified index.
list.Insert(index: 1, item: 5);
Inserts items of another list (or object implementing IEnumerable) into the list at the specified index.
listA.InsertRange(index: 1, collection: listB);
Returns the zero-based index of the last occurrence of the item in the list.
int index = list.LastIndexOf(8);
Returns the index of the last occurrence of the item in the list. It searches the list from the beginning of the list to the specified index.
int index = list.LastIndexOf( item: 8, index: 3);
Returns the index of the last occurrence of the item in the list. It searches in the range specified by count and the end index.
int index = list.LastIndexOf( item: 6, index: 3, count: 2);
Returns -1 if the item is not found in the specified range.
int index = list.LastIndexOf( item: 8, index: 3, count: 2);
Removes the first occurence of the specified item from the list.
Removes all items matching the specified predicate.
list.RemoveAll(x => x < 4);
Removes the item at the specified index.
Removes items from the specified range.
list.RemoveRange(index: 2, count: 3);
Reverses the order of all items in the list.
Reverses the order of the items in the specified range.
list.Reverse(index: 1, count: 2);
Sorts all items in the list.
This List<T> method works only if the type T implements IComparable<T> or IComparable interface.
Sorts list using comparison delegate.
list.Sort((x, y) => x.CompareTo(y));
Sorts list using comparison delegate (in descending order).
list.Sort((x, y) => y.CompareTo(x));
Sorts the list using custom comparer.
list.Sort(new MyComparer());
Sorts the specified range of the list using custom comparer.
list.Sort(index: 2, count: 3, comparer: new MyComparer());
public class MyComparer : IComparer<int>
{
public int Compare(int x, int y) { return x.CompareTo(y); }
}
Creates new array and copies all items into it.
int[] array = list.ToArray();
Returns empty array for empty list.
int[] array = list.ToArray();
Trims the list capacity to reduce memory usage if it's reasonable. It sets Capacity to the same value as Count but only if the Count is less than about 90 % of Capacity.
| list.Count: | 5 |
|---|
| list.Capacity: | 8 |
|---|
list.TrimExcess();
| list.Count: | 5 |
|---|
| list.Capacity: | 5 |
|---|
If the Count is almost the same as the list Capacity it does nothing.
| list.Count: | 7 |
|---|
| list.Capacity: | 8 |
|---|
list.TrimExcess();
| list.Count: | 7 |
|---|
| list.Capacity: | 8 |
|---|
Returns true if all items in the list match the specified predicate.
bool result = list.TrueForAll(x => x < 10);
Returns false if not all items in the list match the specified predicate.
bool result = list.TrueForAll(x => x < 5);
See also
- C# Foreach - how foreach and IEnumerable works debuggable online
- C# Switch - switch statement examples debuggable online
- C# Using - using statement examples debuggable online
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