Is 運算子 (Visual Basic)

發行項
08/12/2011

比較兩個物件參考變數。

result = object1 Is object2

組件

result
必要項。任何 Boolean 值。
object1
必要項。任何 Object 名稱。
object2
必要項。任何 Object 名稱。

備註

Is 運算子會判斷兩個物件參考是否代表同一物件。但是，它不會執行值比較。如果 object1 和 object2 都會參考完全相同的物件執行個體，則 result 為 True，如果不是，則 result 為 False。

Is 也可與 TypeOf 關鍵字搭配使用，以組成 TypeOf...Is 運算式，用以測試物件變數是否會與資料型別相容。

注意事項
Is 關鍵字可以用於 Select...Case 陳述式 (Visual Basic)。

範例

下列範例會使用 Is 運算子，來比較物件參考的配對。結果是指派給代表兩個物件是否完全一樣的 Boolean 值。

Dim myObject As New Object
Dim otherObject As New Object
Dim yourObject, thisObject, thatObject As Object
Dim myCheck As Boolean
yourObject = myObject
thisObject = myObject
thatObject = otherObject
' The following statement sets myCheck to True.
myCheck = yourObject Is thisObject
' The following statement sets myCheck to False.
myCheck = thatObject Is thisObject
' The following statement sets myCheck to False.
myCheck = myObject Is thatObject
thatObject = myObject
' The following statement sets myCheck to True.
myCheck = thisObject Is thatObject

如以上範例所示範，可使用 Is 運算子來測試早期繫結 (Early Bound) 和晚期繫結 (Late Bound) 物件。