Datetime in C# add days

问题:

I want to add days in some date. I have a code like this:

DateTime endDate = Convert.ToDateTime(this.txtStartDate.Text); 
Int64 addedDays = Convert.ToInt64(txtDaysSupp.Text); 
endDate.AddDays(addedDays); 
DateTime end = endDate; 
this.txtEndDate.Text = end.ToShortDateString();

But this code is not working, days are not added! What the stupid mistake I'm doing?

回答1:

DateTime is immutable. That means you cannot change it's state and have to assign the result of an operation to a variable.

endDate = endDate.AddDays(addedDays);

回答2:

You need to catch the return value.

The DateTime.AddDays method returns an object who's value is the sum of the date and time of the instance and the added value.

endDate = endDate.AddDays(addedDays);

回答3:

Its because the AddDays() method returns a new DateTime, that you are not assigning or using anywhere.

Example of use:

DateTime newDate = endDate.AddDays(2);

回答4:

Assign the enddate to some date variable because AddDays method returns new Datetime as the result..

Datetime somedate=endDate.AddDays(2);

回答5:

Use This:

     DateTime dateTime = new DateTime();
     dateTime = DateTime.Now;
     DateTime newDateTime = new DateTime();
    TimeSpan NumberOfDays = new TimeSpan(2, 0, 0, 0, 0);
    newDateTime = dateTime.Add(NumberOfDays);

回答6:

Why do you use Int64? AddDays demands a double-value to be added. Then you'll need to use the return-value of AddDays. See here.

回答7:

you can add days to date like this.

    // add days to current **datetime**
    var addedDateTime = DateTime.Now.AddDays(10);

    // add days to current **date**
    var addedDate = DateTime.Now.Date.AddDays(10);

    // add days to any datetime variable
    var addedDateTime = anyDate.AddDay(10);