How can I make a DateTimePicker display an empty string?

问题

I would like to be able to display a DateTimePicker that has a default value of nothing, i.e. no date.

For example, I have a start date dtTaskStart and an end date dtTaskEnd for a task, but the end date is not known, and not populated initially.

I have specified a custom format of yyyy-MM-dd for both controls.

Setting the value to null, or an empty string at runtime causes an error, so how can I accomplish this?

I have considered using a checkbox to control the enabling of this field, but there is still the issue of displaying an initial value..

Edit:
Arguably a duplicate of the question DateTimePicker Null Value (.NET), but the solution I found for my problem is not a solution for that question, so I think it should remain here for others to find..

回答1:

Just set the property as follows:

When the user press "clear button" or "delete key" do

dtpData.CustomFormat = " "  'An empty SPACE
dtpData.Format = DateTimePickerFormat.Custom

On DateTimePicker1_ValueChanged event do

dtpData.CustomFormat = "dd/MM/yyyy hh:mm:ss"

回答2:

Obfuscating the value by using the CustomFormat property, using checkbox cbEnableEndDate as the flag to indicate whether other code should ignore the value:

If dateTaskEnd > Date.FromOADate(0) Then
    dtTaskEnd.Format = DateTimePickerFormat.Custom
    dtTaskEnd.CustomFormat = "yyyy-MM-dd"
    dtTaskEnd.Value = dateTaskEnd 
    dtTaskEnd.Enabled = True
    cbEnableEndDate.Checked = True
Else
    dtTaskEnd.Format = DateTimePickerFormat.Custom
    dtTaskEnd.CustomFormat = " "
    dtTaskEnd.Value = Date.FromOADate(0)
    dtTaskEnd.Enabled = False
    cbEnableEndDate.Checked = False
End If

回答3:

this worked for me for c#

if (enableEndDateCheckBox.Checked == true)
{
    endDateDateTimePicker.Enabled = true;
    endDateDateTimePicker.Format = DateTimePickerFormat.Short;                
}
else
{
    endDateDateTimePicker.Enabled = false;
    endDateDateTimePicker.Format = DateTimePickerFormat.Custom;
    endDateDateTimePicker.CustomFormat = " ";
}

nice one guys!

回答4:

In case anybody has an issue with setting datetimepicker control to blank during the form load event, and then show the current date as needed, here is an example:

MAKE SURE THAT CustomFormat = " " has same number of spaces (at least one space) in both methods

Private Sub setDateTimePickerBlank(ByVal dateTimePicker As DateTimePicker)    

    dateTimePicker.Visible = True
    dateTimePicker.Format = DateTimePickerFormat.Custom
    dateTimePicker.CustomFormat = "    " 
End Sub


Private Sub dateTimePicker_MouseHover(ByVal sender As Object, ByVal e As 
                    System.EventArgs) Handles dateTimePicker.MouseHover

    Dim dateTimePicker As DateTimePicker = CType(sender, DateTimePicker)
    If dateTimePicker.Text = "    " Then
        dateTimePicker.Text = Format(DateTime.Now, "MM/dd/yyyy")
    End If
End Sub

回答5:

When I want to display an empty date value I do this

            if (sStrDate != "")
            {
                dateCreated.Value = DateTime.Parse(sStrDate);
            }
            else
            {
                dateCreated.CustomFormat = " ";
                dateCreated.Format = DateTimePickerFormat.Custom;
            }

Then when the user clicks on the control I have this:

            private void dateControl_MouseDown(object sender, MouseEventArgs e)
            {
                ((DateTimePicker)sender).Format = DateTimePickerFormat.Long;    
            }

This allows you to display and use an empty date value, but still allow the user to be able to change the date to something when they wish.

Keep in mind that sStrDate has already been validated as a valid date string.

回答6:

The basic concept is the same told by others. But its easier to implement this way when you have multiple dateTimePicker.

dateTimePicker1.Value = DateTime.Now;
dateTimePicker1.ValueChanged += new System.EventHandler(this.Dtp_ValueChanged);
dateTimePicker1.ShowCheckBox=true;
dateTimePicker1.Checked=false;


dateTimePicker2.Value = DateTime.Now;
dateTimePicker2.ValueChanged += new System.EventHandler(this.Dtp_ValueChanged);
dateTimePicker2.ShowCheckBox=true;
dateTimePicker2.Checked=false;

the value changed event function

        void Dtp_ValueChanged(object sender, EventArgs e)
        {
            if(((DateTimePicker)sender).ShowCheckBox==true)
            {
                if(((DateTimePicker)sender).Checked==false)
                {
                    ((DateTimePicker)sender).CustomFormat = " ";
                    ((DateTimePicker)sender).Format = DateTimePickerFormat.Custom;
                }
                else
                {
                    ((DateTimePicker)sender).Format = DateTimePickerFormat.Short;
                }
            }
            else
            {
                ((DateTimePicker)sender).Format = DateTimePickerFormat.Short;
            }
        }

When unchecked

When checked

来源：https://stackoverflow.com/questions/846395/how-can-i-make-a-datetimepicker-display-an-empty-string

标签

.net

winforms

datetimepicker