Category Archives: CodeProject

New Features in C# 6.0 – Primary Constructors


Update: This feature is removed from the C# 6.0 specification, probably for the next version of C#.
Primary constructors reduced declaration of various constructors with different arguments. Primary constructors is declare on the type declaration and this is why it so special. For example:


public class Person (string defaultName)
{
 private string m_Name=defaultName;
 public string Name {get;set;}
 public Person()
 {
   Name=defaultName;
 }

}

We can define Primary Constructor in combination on Auto-Property Initializer on the following way:

public class Person (string defaultName)
{
 private string m_Name=defaultName;
 public string Name {get;set;}=defaultName

}

How to run code daily at specific time in C# Part 2


dailyruncode

Few months ago I wrote blog post about how to run code daily at specific time. I dint know that the post will be the most viewed post on my blog. Also there were several questions how to implement complete example. So today I have decided to write another post, and extend my previous post in order to answer thise question as well as to generalize this subject in to cool demo called Scheduler DEMO.

The post is presenting simple Windows Forms application which calls a method for every minute, day, week, month or year. Also demo shows how to cancel the scheduler at any time.

The picture above shows simple Windows Forms application with two  numeric control which you can set starting hour and minute for the scheduler. Next there is a button Start to activate timer for running code, as well as Cancel button to cancel the scheduler. When the time is come application writes the message on the Scheduler Log.

Implementation of the scheduler

Scheduler is started by clicking the Start button which is implemented with the following code:

/// <summary>
/// Setting up time for running the code
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void startBtn_Click(object sender, EventArgs e)
{

    //retrieve hour and minute from the form
    int hour = (int)numHours.Value;
    int minutes = (int)numMins.Value;

    //create next date which we need in order to run the code
    var dateNow = DateTime.Now;
    var date = new DateTime(dateNow.Year, dateNow.Month, dateNow.Day, hour, minutes, 0);

    listBox1.Items.Add("**********Scheduler has been started!*****");

    //get nex date the code need to run
    var nextDateValue=getNextDate(date,getScheduler());

    runCodeAt(nextDateValue, getScheduler());

}

When the time is defined then the runCodeAt method is called which implementation can be like the following;

/// <summary>
/// Determine the timeSpan Dalay must wait before run the code
/// </summary>
/// <param name="date"></param>
/// <param name="scheduler"></param>
private void runCodeAt(DateTime date,Scheduler scheduler )
{
    m_ctSource = new CancellationTokenSource();

    var dateNow = DateTime.Now;
    TimeSpan ts;
    if (date > dateNow)
        ts = date - dateNow;
    else
    {
        date = getNextDate(date, scheduler);
        ts = date - dateNow;
    }

    //enable the progressbar
    prepareControlForStart();

    //waits certan time and run the code, in meantime you can cancel the task at anty time
    Task.Delay(ts).ContinueWith((x) =>
        {
            //run the code at the time
                methodToCall(date);

                //setup call next day
                runCodeAt(getNextDate(date, scheduler), scheduler);

        },m_ctSource.Token);
}

The method above creates the cancelationToken needed for cancel the scheduler, calculate timeSpan – total waiting time, then when the time is come call the method methodToCall and calculate the next time for running the scheduler.

This demo also shows how to wait certain amount of time without blocking the UI thread.

The full demo code can be found on OneDrive.

New Features in C# 6.0 – Auto-Property Initializers


Initialize property is repetitive task, and cannot be done in the same line as we can can done for fields. For example we can write:


public class Person
{
 private string m_Name="Default Name";
 public string Name {get;set;}
 public Person()
 {
   Name=m_Name;
 }

}

As we can see Property can be initialized only in the constructor, beside the filed which can be initialized in the same line where it is declared. The new feature in C# 6.0 defines Auto-Property initializer alowing property to be initialized like fields. The following code snippet shows the Auto-Property Initializer;


public class Person
{
 static string m_Name="Default Name";
 static string Name {get;set;}=m_Name;
}

New Features in C# 6.0 – Null-Conditional Operator


This is blog post series about new features coming in the next version of C# 6.0. The first post is about null conditional operator.

The NullReferenceException is night mare for any developer specially for developer with not much experience. Almost every created object must be check against null value before we call some of its member. For example assume we have the following code sample:

class Record
{
 public Person Person  {get;set;}
 public Activity Activity  {get;set;}
}
public static PrintReport(Record rec)
{
  string str="";
   if(rec!=null && rec.Person!=null && rec.Activity!=null)
   {
     str= string.Format("Record for {0} {1} took {2} sec.", rec.Person.FirstName??"",rec.Person.SurName??"", rec.Activity.Duration);
     Console.WriteLine(str);
   }

  return ;
}

We have to be sure that all of the object are nonnull, otherwize we get NullReferenceException.

The next version of C# provides Null-Conditional operation which reduce the code significantly.

So, in the next version of C# we can write Print method like the following without fear of NullReferenceException.


public static PrintReport(Record rec)
{
  var str= string.Format("Record for {0} {1} took {2} sec.", rec?.Person?.FirstName??"",rec?.Person?.SurName??"", rec?.Activity?.Duration);
     Console.WriteLine(str);

  return;
}

As we can see that ‘?’ is very handy way to reduce our number of if statements in the code. The Null-Conditional operation is more interesting when is used in combination of ?? null operator. For example:


 string name=records?[0].Person?.Name??"n/a";

The code listing above checks if the array of records not empty or null, then checks if the Person object is not null. At the end null operator (??) in case of null value of the Name property member of the Person object put default string “n/a”.

For this operation regularly we need to check several expressions agains null value.
Happy programming.

 

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