How to convert a string to a datetime

Question

I have a query built that uses a start date and end date which are both of type datetime. I then have another variable called withinPastTime that is supposed to take in a string and query based on that many hours back. Example if the user enters 24 it will search within a 24 hour period.

C#

withinthepast.Text = History.QueryInfo.WithinPastTime;
                startdatetext.Text = DateTime.Parse(History.QueryInfo.StartDate).ToString("M/d/yyyy");
                enddatetext.Text = DateTime.Parse(History.QueryInfo.EndDate).ToString("M/d/yyyy");

ASP view

<div class="row-fluid">
                        <div class="span8">

                            <div class="row">
                                <div class="span1">
                                    <asp:RadioButton ID="RadioButton1" runat="server" Checked="True" GroupName="DateQuery"/>
                                </div>
                                <div class="span11">
                                    <span class="label">Start Date</span><br />
                                    <asp:TextBox ID="startdatetext" runat="server" MaxLength="10"></asp:TextBox>
                                    <asp:Image ID="startimage" runat="server" ImageUrl="Images/calender16.png" />
                                    <!-- note: do not add and ID attribute to the AJAX:CalenderExtender -->
<%--                                    <ajax:CalenderExtender runat="server" TargetControlID="startdatetext" PopupButtonID="startimage" />--%>
                                </div>
                            </div>
                            <div class="row">
                                <div class="span1">
                                </div>
                                <div class="span11">
                                    <span class="label">&nbsp;End Date&nbsp;</span><br />
                                    <asp:TextBox ID="enddatetext" Enabled="true" runat="server" MaxLength="10"></asp:TextBox>
                                    <asp:Image ID="endimage" runat="server" ImageUrl="Images/calender16.png" />
                                    <!-- note: do not add and ID attribute to the AJAX:CalenderExtender -->
<%--                                    <AJAX:CalenderExtender runat="server" TargetControlID="enddatetext" PopupButtonID="endimage" />--%>
                                </div>
                            </div>
                            <br />
                            OR
                            <br />
                            <br />                    
                            <div class="row">
                                <div class="span1">
                                    <asp:RadioButton ID="RadioButton2" runat="server" GroupName="DateQuery"/>
                                </div>
                                <div class="span11">
                                    <span class="label">Within the past (hours)</span><br />
                                    <asp:TextBox ID="withinthepast" Enabled="true" runat="server" Text="1"></asp:TextBox>
                                    <asp:Image ID="upimage" runat="server" ImageUrl="Images/arrowup16.png" />
                                    <asp:Image ID="downimage" runat="server" ImageUrl="Images/arrowdown16.png" />
                                    <!-- note: do not add and ID attribute to the NumericUpDownExtender -->
                                    <ajax:NumericUpDownExtender runat="server" Minimum="1" Width="75"
                                        TargetControlID="withinthepast" TargetButtonUpID="upimage" TargetButtonDownID="downimage" />
                                </div>
                            </div>

                        </div>
                        <div class="span4">
                            <div class="btn-group btn-group-vertical" data-toggle="buttons-checkbox">
                                <span class="label" style="margin-top: 5px;">Dates in Range</span>
                                <asp:CheckBoxList ID="timerange" runat="server" style="border-style:solid;float:left;border-width:1px;margin:10px;" Width="120px">
                                    <asp:ListItem Text="Scheduled At" Selected="True"></asp:ListItem>
                                    <asp:ListItem Text="Scheduled For" Selected="True"></asp:ListItem>
                                    <asp:ListItem Text="Submitted" Selected="True"></asp:ListItem>
                                    <asp:ListItem Text="Started" Selected="True"></asp:ListItem>
                                    <asp:ListItem Text="Completed" Selected="True"></asp:ListItem>
                                </asp:CheckBoxList>
                            </div>
                        </div>
                    </div>

    DateTime withinthepast = Date.Evaluate(m_Owner.QueryInfo.WithinPastTime, DateTime.Now(- **this is where my withinthepastvariable would go telling DateTime.Now how many hours to subtract));

Any thoughts?

Answer 1

You can switch withinPastTime to be an int then you can use the AddHours () method as so:

DateTime.Now.AddHours(withinPastTime);

You can pass negative values to make it go back in time.

This will also restrict any input to be a valid number, other stings would throw an exception.

Answer 2

我认为您需要的是AddHours ：

DateTime.Now.AddHours(-pastHours)