类型或名称空间可以找到-即使我声明了变量

Question

i am getting this error:

The type or namespace name 'myObject' could not be found

on this line:

if (typeof(myObject) != typeof(String))

here is the surrounding code:

 for (int rCnt = 1; rCnt <= EmailList.Rows.Count; rCnt++)
            {
                object myObject = (EmailList.Cells[rCnt, 1] as Excel.Range).Value2;
                if (typeof(myObject) != typeof(String))
                    continue;
                cell = (string)(EmailList.Cells[ rCnt,1] as Excel.Range).Value2;
                if (cell!=null)
                    emails.Add(cell.ToString());
            }

what am i doing wrong? i'm obviously declaring myObject. thanks so much for your guidance.

Answer 1

The typeof operator takes a type identifier, not an instance identifier, as the argument.

You want myObject.GetType() to get the type of an object:

if (myObject.GetType() != typeof(String))

Or even use the is operator instead:

if (!(myObject is String))

Answer 2

typeof only works on a type name.

You want:

if (myObject.GetType() != typeof(String))

You can also use the is operator:

if (!(myObject is String))

The difference only shows up when you are dealing with inheritance.

DerivedInstance.GetType() == typeof(BaseType) // false
DerivedInstance is BaseType // true

As mentioned in comments, null is an issue. If DerivedInstance is actually null:

DerivedInstance.GetType() == typeof(BaseType) // NullReferenceException
DerivedInstance is BaseType // false

Answer 3

您需要myObject.GetType（）或可以使用

if ((myObject as string)==null)

Answer 4

as BoltClock's a Unicorn mentioned, in this case you need GetType() . In addition, the whole code you wrote is unnecessary.

            object myObject = (EmailList.Cells[rCnt, 1] as Excel.Range).Value2;
            if (typeof(myObject) != typeof(String)) // !(myObject is String) is enough. Plus, this won't work, if myObject is null.
                continue;
            cell = (string)(EmailList.Cells[ rCnt,1] as Excel.Range).Value2; // you can operate with myObject here as well
            if (cell!=null) // in case of object having type, this is unnecessary.
                emails.Add(cell.ToString()); // why calling ToString() on string?

the only thing you need is

string str = (EmailList.Cells[rCnt, 1] as Excel.Range).Value2 as string;
if (str != null)
    emails.add(str);

Answer 5

typeof is for types and not for instances , change it to

myObject.GetType()

Here are different solutions:

if (myObject.GetType() != typeof(String))

if (!(myObject is String))

if ((myObject as String)==null)

Answer 6

typeof takes a type as an argument. You've passed it an object instead. What you are probably trying to do is:

if (myObject.GetType() != typeof(string))