An arraylist is a combination of an array and a collection.
legacy only used for backwards compatibility
Upgrade to Generic.List<T>
This allows you to work with a set of values as if they were an array and a collection at the same time.
An arraylist has the following functionality:
You can address a value by its index
You can quickly sort and reverse the list
You can search sequentially
You can append elements to the end and insert them in a particular position
You can remove any element
Expands automatically as more elements are added (just like a collection)
Imagine that you need to keep track of various objects but you have no idea how many.
It is difficult to use an array for this purpose because you must declare the size of the array at compile time
The ArrayList is a class designed specifically for this situation
This is an aray whose size is dynamically increased as required.
The default capacity for a new arraylist is 16 elements.
Dim aliArrayListIntegers As New System.Collections.ArrayList
You should always try and define an initial capacity for your arraylist if possible.
This defines an arraylist with an initial capacity of 200 elements.
Dim aliArrayListIntegers As New System.Collections.ArrayList(200)
You can modify the capacity at any time by assigning a value to the Capacity property
aliArrayListIntegers.Capacity = aliArrayListInteger.Count
Another way to achieve the same result is to use the TrimToSize property
When the current capacity is exceeded the ArrayList will automatically double its capacity.
It is possible to initialise an arraylist and to poulate it with an initial value
Dim aliArrayListIntegers As New System.Collections.ArrayList.Repeat(-1,200)
Dim alsArrayListStrings As New System.Collections.ArrayList.Repeat("",200)
The ArrayList class fully implements the IList interface with all the familiar methods.
|Add||Appends an element after the last element in the collection and returns the index where it was inserted.|
|Capacity||Property contains the number of elements the srray can currently hold.|
|Clear||Removes all elements from the collection.|
|Contains||Returns TRUE if an element exists in the collection.|
|CopyTo||Copies the elements from the collection to a new one-dimensional array, starting at the specified index in the array.|
|Count||Returns the number of elements in the collection.|
|GetEnumerator||Method that returns an enumerator to iterate an ArrayList|
|IndexOf||Returns the index of the element in the collection, or -1 if it cannot be found.|
|Insert||Inserts an element at the specified index.|
|IsFixedSize||Returns TRUE if no more elements can be added to the collection.|
|IsReadOnly||Returns TRUE is the elements cannot be altered.|
|Item||Gets or sets the elements at the specified 0-based index.|
|Remove||Removes an element from the collection|
|RemoveAt||Removes an element at the specified index from the collection|
|Reverse||Method that reverses the order of the elements|
|Sort||Method that alphabetically sorts the elements|
|ToArray||Method that copies all the elements to a new one-dimensional array|
Do not return Nothing
Return New System.Collections.ArrayList
Does an Element Exist
If (alArrayList.Contains(sElement) = True) Then
Removing an Element
The Remove method will only remove the first occurrence of an element.
Also this method does not generate an exception if the element you want to remove cannot be found.
There are two ways you can remove all the instances of an element.
This method is very concise but not very efficient.
You can also use the contain method.
Do While alsArrayListStrings.IndexOf("remove this") >= 0
This is far more efficient, this loops until the count property becomes constant.
Dim isavecount As Integer
isavecount = alsArrayListStrings.Count
Loop While (alsArrayListStrings.Count < isavecount)
Converting to a String Array
Dim arValues() As String
Dim arArrayList As System.Collections.ArrayList
arValues = DirectCast(arArrayList.ToArray(GetType(String)),String())
© 2021 Better Solutions Limited. All Rights Reserved. © 2021 Better Solutions Limited TopPrevNext