When one should use Set [e.g for SpecialCells return value]?

问题

I am afraid I misunderstand the documentation of VBA for excel, I have this line which seems to be an error:

Range a = Selection.SpecialCells(xlCellTypeConstants, 23)

But this one is just fine:

Set a = Selection.SpecialCells(xlCellTypeConstants, 23)

The documentation claims:

Returns a Range object that represents all the cells that match the specified type and value.

But it actually returns a byRef object and that is why I have to use Set.

What do I miss here?

Here is Range.SpecialCells method help in Excel:

回答1:

Range a = Selection.SpecialCells(xlCellTypeConstants, 23)

This is not valid VBA, regardless of data type. You don't declare variable type in front of variable name, as you would do in C#, and you don't initialize variable at the point of declaration, as you would do in VB.NET.

You can do:

Dim a As Range
Set a = Selection.SpecialCells(xlCellTypeConstants, 23)

This will save a reference to the range into a.

You can also do:

Dim a As Variant
a = Selection.SpecialCells(xlCellTypeConstants, 23)

This will save in a a 2D array of values of cells in the range.

Returns a Range object that represents all the cells that match the specified type and value.

But it actually returns a byRef object and that is why I have to use Set.

There are no byval objects in VBA. All objects are byref, and when you want to copy a reference to an object, you always use Set. The reason why you need Set is default properties. Each object can have a default property that is requested when only object name is provided. This creates ambiguity, so you need to say Set when you need to manipulate the object reference itselt, and omit Set when you want the default property of an object. The default property of Range is Value.

回答2:

Object variables are assigned using the Set keyword. Non-object variables (let's ignore variants for now) do not use the Set keyword

dim a as int
dim b as string
dim c as boolean

a = 1
b = "hello"
c = false

dim a as Range
dim b as Worksheet
dim c as PivotTable

set a = ActiveSheet.Range("a1")
set b = ActiveSheet
set c = ActiveSheet.PivotTables(1)

回答3:

Range.SpecialCells Method returns a Range object that represents all the cells that match the specified type and value. set keyworkd is used to assign a reference to an object.

There are two flavors of assignments in VBA: one for ordinary variables, which use Let, and one for object variables, which use Set.

An ordinary (string, logical, numeric) variable is one that points to the location in memory where the variable is stored.

An object variable (all the things you find in the language reference under Objects) is one that points to a structure in memory (a VTable) that in turn contains pointers to the object's properties and methods.

Reference http://www.excelforum.com/excel-programming-vba-macros/693357-when-to-use-the-keyword-set.html

回答4:

Do not know it this matters, but Value is not default property of Range. Default property of Range is _Default.

It is defined like this _Default([in, optional] VARIANT RowIndex, [in, optional] VARIANT ColumnIndex) and it represents the array of values of particular range.

Sub test()

    Dim rng As Range
    Set rng = ActiveSheet.Range("A1:C3")

    ' all cells in range rng become value of 1
    rng.Value = 1

    ' all cells in range rng become now value of 2
    rng.[_Default] = 2

    ' first cell in range rng become value of 3
    rng.[_Default](1, 1) = 3

    ' nothing changes
    rng.Value()(1, 1) = 4

    Dim a1, a2
    ' however both Value and _Default return same array of variants
    a1 = rng.Value
    a2 = rng.[_Default]

End Sub

来源：https://stackoverflow.com/questions/17877536/when-one-should-use-set-e-g-for-specialcells-return-value

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