title: Date to String [format string] String to Date in Swift
body: <p>I've racked my brain over this issue all day and can't seem to get a solution.  I have a fitness program that queries the Health Data Store.  In the predicateForSamples(withStart: myStartDate, end: myEndDate) I am finding that getting a date from a datePicker sends a moment in time and therefore my query does not return the results for the entire day as I'd like.  So, I figured if I take that datePicker date and convert it to a starting and ending format my issue would be solved.  However, using the let date = dateFormatter.date(from: dateString) is returning the correct date but the time returns as 04:00:00 +0000 for both functions.  </p>
  
  <p>If anybody has a suggestion, please feel free to lend a helping hand.  Thank you so very much!</p>
  
  <pre><code>func convertStartDate(StartDate: Date) -&gt; Date {
  
      let dateFormatter = DateFormatter()
      dateFormatter.dateFormat = "yyy-MM-dd '00':'00':'01' +0000"
      let dateString = dateFormatter.string(from: StartDate)
      print("convertingStartDate() - \(dateString)")
      let date = dateFormatter.date(from: dateString)
      print(date as Any)
  
      return date!
  }
  
  func convertEndDate(EndDate: Date) -&gt; Date {
  
      let dateFormatter = DateFormatter()
      dateFormatter.dateFormat = "yyy-MM-dd '23':'59':'59' +0000"
      let dateString = dateFormatter.string(from: EndDate)
      print("convertingEndDate() - \(dateString)")
      let date = dateFormatter.date(from: dateString)
  
      return date!
  }
  </code></pre>