From Xojo Documentation
|You are currently browsing the old Xojo documentation site. Please visit the new Xojo documentation site!|
Arrays are an indexed collection of data for a specific data type. Arrays themselves are not a data type, but any data type can be defined as an array using the Var statement or as a property.
Var arrayName() As dataType
Var arrayName(size [,size2,...sizeN]) As dataType
Var arrayName(), arrayNameN() As dataType [= Array(value1, value2, ..., valueN)]
|arrayName||Variable name||The name of the array.|
|size||Integer||(Optional) The size of the array. Size must be integer literals or integer constants.
If you do not specify a size, then array starts as empty. You can add elements using the Add method.
|sizeN||Integer||(Optional) The size of the next dimension of the array if you are creating a multi-dimensional array.
You pass as many size parameters as dimensions in the array. The size parameters must be integer literals or integer constants.
|dataType||Data type or class||The data type or class of the array.|
|value1...valueN||values||Values that match the dataType to add to the array.|
Arrays can have a maximum index value of 2,147,483,646 for both 32-bit and 64-bit apps. In addition, although the methods Count, FirstIndex, IndexOf and LastIndex all indicates they return an Integer, they technically return an Int32 (even with 64-bit app). If you are creating Extension methods on Integer you should keep this in mind as you may also want to create Int32 extension methods as well.
Arrays are treated as objects so be aware that assigning an array to another variable or passing an array as a parameter does not make a copy of the array. Instead you get a new variable that points to the original array so any changes you make to the "2nd" array also affects the first array. If you need an actual copy of the array you will have to manually copy its values using a loop.
Arrays are often created by specifying the size of the array when you create it. Because arrays all start at position 0, an array has one more element than the number you use as the size. For example, this creates an array with 5 elements, which you can then access using the index:
aNames(0) = "Bob"
aNames(1) = "Bill"
aNames(2) = "Ben"
aNames(3) = "Brad"
aNames(4) = "Bart"
Constants can be used when declaring the size of an array:
You can also create empty arrays that do not specify a size. An empty array has a size of -1. At run-time, your code can add elements to it or you can choose to make it a specific size by using Arrays.ResizeTo. These are the two ways to create an empty array:
If you try to access an element of an array that does not exist, you will get an OutOfBoundsException. Here are some examples that would raise the exception:
aFirstName(1) = "Bill" // aFirstName is still empty
Use the methods Add and AddAt to add additional elements to arrays. These methods are the only ways to add elements to empty arrays, but they can also be used to extend the size of any single-dimension array.
Iterating Through an Array
If you need to access each element of an array but don't need to know the index of that element, you can use an iterator:
For Each name As String In People
You can also cycle through an array by index:
For index As Integer = 0 To people.LastIndex
Var name As String = people(index)
There is no real advantage to caching the array's last index in a variable to use in a loop. Over millions of iterations, it will only save a few milliseconds.
If the array is stored in a variant, you must cast the variant as an array in order to access it.
A multi-dimensional array has elements in 2 or more dimensions. A table would be an example of a 2-dimensional array because it has columns and rows.
Most of the array methods are not supported for multi-dimensional arrays.
You declare multi-dimensional arrays by specifying the size for each dimension:
Remove All Elements
The fast way to remove all elements from an array is to use Arrays.RemoveAll:
For i As Integer = 1 To 1000
// myArray is now empty
Objects in Arrays
Arrays of objects work like other arrays except you'll have to deal with possible Nil values just as you would with objects that are not in an array.
If the array index is valid and its value is Nil and you try to use the value, then you get a NilObjectException, just as you would if you try to use any non-array value that is Nil.
If an array index is not valid then that’s an OutOfBoundsException and is not related to anything being Nil.