Introduction
This article shall describe a very simple approach to finding out the first and
last day of the month based upon either a selected date or selected month. There
are other ways to accomplish the task aside from what is presented in this
article; however, this approach is reliable and quite easy to use and does not
involve the typical approach of using time spans to resolve the question.
The use of such an approach may be of some value if, for example, one were
writing an application that queries a database and the queries were to be bound
to return result sets limited to a single month starting always with the first
day of the month and ending with the last day of the month.
Naturally, resolving the first day of the month is not much of an issue; it is
pretty safe to assume the first day of the month is going to be the first.
However, I show calculating the first day of the month in a similar manner so as
to permit the involved function to return a DateTime value in response to a
request for the first day of the month. One could also obtain a DateTime value
by taking the month and year from the current date and the either subtracting
the appropriate number of days from the date to set it to the first or by
creating a new DateTime variable and instancing it with the selected dates month
and year along with manually setting the new date day to 1 as shown below.
Dim dt As New DateTime(dtpDate.Value.Year,
dtpDate.Value.Month, 1)
The value of returning the date as a DateTime value would be apparent if one
were required to perform some DateTime related functions on the returned value.
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Figure 1: Finding the First and Last Days of a Month
Getting Started
The solution contains a single Windows Forms project called FirstLastDayVB which
was written in VB.NET; the application contains a single Windows form
(Form1.vb); this form contains all of the code necessary to calculate and
display the first and last days of the month. That portion of the code used to
determine the first and last days of the month could have just as easily been
placed into a separate static class accessible by the main application form.
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Figure 2: Solution
Explorer with the Project Visible
Code: Main
Form (Form1.vb)
This form class is used to demonstrate the use of the methods used to calculate
and display the first and last days of the month. The form class is pretty
simple and the annotation provided describes the purpose of each part of the
class. The form itself, visible in Figure 1, contains a collection of controls
used to set the input values used by the class methods, and to display the
results to the user.
<summary>
Example of one approach to obtaining the first
and last days of any given month
</summary>
<remarks>none</remarks>
Public Class Form1
The
constructor is shown following the class declaration; it has been modified to
load an array containing a list of all of the months into a ComboBox and to set
the control to display the first item in its collection upon initialization.
#Region "Constructor"
<summary>
Constructor
</summary>
<remarks></remarks>
public Sub New()
This call is required by the Windows Form Designer.
InitializeComponent()
Add any initialization after the InitializeComponent() call.
Dim months() As String =
{"January", "February", "March", "April", "May", "June", "July", "August","September", "October", "November", "December"}
populate a combobox with all of the months
cboMonths.Items.AddRange(months)
select an item
cboMonths.SelectedIndex = 0
End Sub
#End Region
The
click event handlers region follows; this section actually calls the class
methods used to retrieve the first and last of the month date values and in turn
displays that information to the user. The annotation describes the code.
#Region "Click
Event Handlers"
<summary>
Find and display the first and last day of the month for the supplied date
</summary>
<param name="sender"></param>
<param name="e"></param>
<remarks></remarks>
Private Sub btnFind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) HandlesbtnFind.Click
set the calendar date and click the find button to report the first and last day
of the month for any month selected in the date time picker control set first
day
txtFirstDay.Text = GetFirstDayOfMonth(dtpDate.Value).ToShortDateString()
get day of week for first day
Dim dateParts() As String =
txtFirstDay.Text.Split("/")
Dim dtFirstTemp As New DateTime(Convert.ToInt32(dateParts(2)),
Convert.ToInt32(dateParts(0)), Convert.ToInt32(dateParts(1)))
display day of week in label
lblDowFirst1.Text = dtFirstTemp.DayOfWeek.ToString()
set last day
txtLastDay.Text = GetLastDayOfMonth(dtpDate.Value).ToShortDateString()
get day of week for last day
Dim dateParts2() As String =
txtLastDay.Text.Split("/")
Dim dtLastTemp As New DateTime(Convert.ToInt32(dateParts2(2)),
Convert.ToInt32(dateParts2(0)), Convert.ToInt32(dateParts2(1)))
display day of week in label
lblDowLast1.Text = dtLastTemp.DayOfWeek.ToString()
End Sub
<summary>
Execute the code to set the first and last day of the month by passing in only
an integer representation of the month
</summary>
<param name="sender"></param>
<param name="e"></param>
<remarks></remarks>
Private Sub btnFind2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) HandlesbtnFind2.Click
set the calendar date and click the find button to report the first and last day
of the month for any month selected in the date time picker control set first
day
txtFirstDay2.Text = GetFirstDayOfMonth(cboMonths.SelectedIndex
+1).ToShortDateString()
get day of week for first day
Dim dateParts() As String =
txtFirstDay2.Text.Split("/")
Dim dtFirstTemp As New DateTime(Convert.ToInt32(dateParts(2)),
Convert.ToInt32(dateParts(0)), Convert.ToInt32(dateParts(1)))
display day of week in label
lblDowFirst2.Text = dtFirstTemp.DayOfWeek.ToString()
set last day
txtLastDay2.Text = GetLastDayOfMonth(cboMonths.SelectedIndex +
1).ToShortDateString()
get day of week for last day
Dim dateParts2() As String =
txtLastDay2.Text.Split("/")
Dim dtLastTemp As New DateTime(Convert.ToInt32(dateParts2(2)),
Convert.ToInt32(dateParts2(0)), Convert.ToInt32(dateParts2(1)))
display day of week in label
lblDowLast2.Text = dtLastTemp.DayOfWeek.ToString()
End Sub
<summary>
Exit the application
</summary>
<param name="sender"></param>
<param name="e"></param>
<remarks></remarks>
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) HandlesbtnExit.Click
Application.Exit()
End Sub
#End Region
The last
region in the class contains the methods used to get the first and last days of
the month. The region provides four methods, one gets the first day of the month
based upon receipt of a date, one gets the first day of the month based upon
receipt of an integer value representing a month, one gets the last day of the
month based upon receipt of a date, one gets the last day of the month based
upon receipt of an integer value representing a month. The
annotation describes the process used in each method.
#Region "Private
Methods"
<summary>
Get the first day of the month for any full date submitted
</summary>
<param name="dtDate"></param>
<returns></returns>
Private Function GetFirstDayOfMonth(ByVal dtDate As DateTime) As DateTime
set return value to the first day of the month for any date passed in to the
method
create a datetime variable set to the passed in date
Dim dtFrom As DateTime
= dtDate
remove all of the days in the month except the first day and set the variable to
hold that date
dtFrom =
dtFrom.AddDays(-(dtFrom.Day - 1))
return the first day of the month
Return dtFrom
End Function
<summary>
Get the first day of the month for a month passed by it's integer value
</summary>
<param name="iMonth"></param>
<returns></returns>
Private Function GetFirstDayOfMonth(ByVal iMonth As Int32) As DateTime
set return value to the last day of the month for any date passed in to the
method
create a datetime variable set to the passed in date
Dim dtFrom As New DateTime(DateTime.Now.Year,
iMonth, 1)
remove all of the days in the month except the first day and set the variable to
hold that date
dtFrom =
dtFrom.AddDays(-(dtFrom.Day - 1))
return the first day of the month
Return dtFrom
End Function
<summary>
Get the last day of the month for any full date
</summary>
<param name="dtDate"></param>
<returns></returns>
Private Function GetLastDayOfMonth(ByVal dtDate As DateTime) As DateTime
set return value to the last day of the month for any date passed in to the
method create a datetime variable set to the passed in date
Dim dtTo As DateTime
= dtDate
overshoot the date by a month
dtTo =
dtTo.AddMonths(1)
remove all of the days in the next month to get bumped down to the last day of
the previous month
dtTo =
dtTo.AddDays(-(dtTo.Day))
return the last day of the month
Return dtTo
End Function
<summary>
Get the last day of a month expressed by it's integer value
</summary>
<param name="iMonth"></param>
<returns></returns>
Private Function GetLastDayOfMonth(ByVal iMonth As Int32) As DateTime
set return value to the last day of the month for any date passed in to the
method
create a datetime variable set to the passed in date
Dim dtTo As New DateTime(DateTime.Now.Year,
iMonth, 1)
overshoot the date by a month
dtTo =
dtTo.AddMonths(1)
remove all of the days in the next month to get bumped down to the last day of
the
previous month
dtTo =
dtTo.AddDays(-(dtTo.Day))
return the last day of the month
Return dtTo
End Function
#End Region
End Class
Summary
This article was intended to demonstrate a simple approach to obtaining the
first and last days of a month using a four methods each of return a DateTime
value containing either the first or last day of the month. The code could be
useful if one were defining something, such as SQL query terms, which required
single month ranges of dates based upon user selections of single dates or
months. There are of course other ways to do this but this one is pretty simple.