How to subtract a month from Date object?

问题:

How do I subtract a month from a date object in VB.NET?

I have tried:

Today.AddMonths(-1)

However, given that Today is 01-Jan-2010, the result I get is 01-Dec-2010. The answer I want is 01-Dec-2009.

Is there a convenient way of doing this within the .NET framework?

回答1:

You actually have to transport Today into a variable and let that assignment work there. The following code will produce the result you expect (I just verified it because your post made me think twice).

Dim dt As DateTime = Date.Today
dt = dt.AddMonths(-2)

Dim x As String = dt.ToString()

回答2:

This works fine, you need to remember that the DateTime is imutable.

Dim d As DateTime
d = New DateTime(2010, 1, 1)
d = d.AddMonths(-1)

Have a look at DateTime Structure

A calculation on an instance of DateTime, such as Add or Subtract, does not modify the value of the instance. Instead, the calculation returns a new instance of DateTime whose value is the result of the calculation.

回答3:

Dim d As DateTime = #1/1/2010#
d = d.AddMonths(-1)

回答4:

I have used the following and it works.

Dim dtToday As DateTime = Date.Today
dtToday = dtToday.AddMonths(-2)