在C＃中处理元素

Question

I am automating some tasks with the help of a database and WPF C# applications. One such task is monthly reporting, looking at activity from the previous month. I am using DateTime pickers to pick a start and end date for the reporting, but usually it will be the first and last day of whatever month. In my view model I have binding properties to the begin date time and the end date time, and they default to the first and last day of the previous month. When I pick a new start day, I have code that will make it the first day of the picked month, and then set the end day to the last day of the month like so:

private DateTime _d1 = new DateTime(DateTime.Today.Year, DateTime.Today.Month - 1, 1); //First Day of previous month
private DateTime _d2 = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1).AddDays(-1); //Last Day of previous month
public DateTime d1
    {
        get { return _d1; }
        set
        {
            if (value != _d1)
            {
                _d1 = new DateTime(value.Year, value.Month, 1);
                _d2 = new DateTime(value.Year, value.Month + 1, 1).AddDays(-1);
                RaisePropertyChangedEvent("d1");
                RaisePropertyChangedEvent("d2");
            }
        }
    }

So my question is this: the old DateTime that _d1 was referencing (same for _d2 ) is still allocated out there somewhere. Is there a way for me to dereference that block of memory before assigning a new one? I figure that garbage collection probably does this, but it seems strange to me to leave things dangling like that. Coming from a C/C++ background, I feel that this is definitely not ok.

Answer 1

In the case of DateTime you are fine. Its all managed memory and the GC will get it.

You do need to be careful about this with objects that use unmanaged resources, specifically, if they implement IDisposable .

For such objects, you should call Dispose when you are done with them or use them in a using block so they will be disposed when they leave scope:

using (var someDisposable = new DisposableObject())
{
   //do stuff with someDisposable
}

Bitmap is a good example of a class that will bite you if you forget this :) It holds a large un-managed GDI bitmap that will take forever to clear if you don't manually dispose it.