How do I – Validate user input is numeric from Powershell?

Written by Cornelius J. van Dyk on . Posted in Blog

As the level of complexity and power of our Powershell scripts increase, it is inevitable that we reach a point where we need to interact with the user and prompt them for some information.  In this case we were building a script to automate the creation and scaling of Search so we needed to know how many servers would be configured as Crawl servers.  We all know the Read-Host cmdlet can provide us with the input, but how do we know that the user actually entered numeric only data?  The easiest way is to simply use a try/catch block and attempt to convert the input to an int value.  Here’s how we do that:

$numberOfCrawl = 0
$inputOK = $false
do
{
  try
  {
    [int]$numberOfCrawl = Read-Host -ForegroundColor red "Please enter the number of servers you wish to configure as Crawl servers."
    $inputOK = $true
  }
  catch
  {
    Write-Host -ForegroundColor red "INVALID INPUT!  Please enter a numeric value."
  } 
}
until ($inputOK)
Write-Host –ForegroundColor green "You chose to configure [$numberOfCrawl] Crawl servers."

We start by defining the $inputOK variable as false and then wrap the entire piece of code in a do/until loop that repeats until the user enters a valid numeric only value.  Inside of this loop, we have a try/catch block.  Inside the try, we attempt to assign the entered value from Read-Host to the $numberofCrawl variable which we cast as an int.  If the user enters a non-numeric value, the cast will fail and will be caught by the catch.  In the catch we output an error message in red text and simply allow the loop to restart from the top.  If however, the user entered a valid numeric value, the cast will succeed afterwich we set the $inputOK variable to true thus allowing the loop to end gracefully.  As a final step, we display the entered value to the user.



Cheers
C




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How do I – Sort a list of custom class objects in descending order in C#?

Written by Cornelius J. van Dyk on . Posted in Blog, How Do I...

Suppose we have a custom class defined thus:

    class CustomClass
    {
        public string String1 { get; set; }
        public string String2 { get; set; }
        public string String3 { get; set; }
        public int Int1 { get; set; }
        public int Int2 { get; set; }

        public CustomClass()
        {
            String1 = "";
            String2 = "";
            String3 = "";
            Int1 = 0;
            Int2 = 0;
        }

        public int Calculate()
        {
            return Int1 + Int2;
        }
    }
As we can see, the class initializes it’s variables and has a Calculate() method that simply returns the added value of the two int variables of the class. Now suppose we have a list of these class objects in our app with varying values thus:
    CustomClass MyClass = new CustomClass();
    MyClass.Int1 = 10;
    MyClass.Int2 = 5;
    CustomClass My2ndClass = new CustomClass();
    My2ndClass.Int1 = 7;
    CustomClass My3rdClass = new CustomClass();

    List lst = new List();
    lst.Add(My2ndClass); 
    lst.Add(MyClass);
    lst.Add(My3rdClass);
We now have a list containing 3 of our custom class objects. The first object in the list has an Int1 value of 10. The second has an Int1 value of 5 and the third, given the class’ initialization method, will have an Int1 value of 0. Given the order that we added the class objects to our list, the list, when looking at the Int1 field would look thus: 7, 10, 0 How do we go about sorting this list by any one of the variable fields of the custom class, say Int1 in our case? The built in support for Linq in Visual C# and the .NET Framework, actually makes this very easy. Using a Lambda expression, the task becomes a one liner thus:
  lst = lst.OrderByDescending(x => x.Int1).ToList();
We start with the OrderByDescending() method and then pass the Lambda expression to reference back to the object itself. The x => part of the expression tells C# to reference back to the calling object which in our case is lst. C# will reference back to lst as x which is where the x.Int1 then instructs the OrderByDescending method to use the Int1 field as the value by which to sort, in descending order, the x object which translates to lst. By appending the ToList() method to the back of the statement, C# will take the sorted result and generate a new List<> object which we simply assign back to the original lst variable. If we needed to sort in ascending order we would use the OrderBy() method instead thus making the statement:
 lst = lst.OrderBy(x => x.Int1).ToList();


Cheers
C




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How do I – Play the TNG Red Alert (or any audio file for that matter) in my WinForms C# app

Written by Cornelius J. van Dyk on . Posted in Blog, How Do I...

Out of the box, C# and .NET supports the playing of any .WAV file.  The code is pretty straight forward.  We simply need to reference the system media class to create a SoundPlayer{} object thus:

System.Media.SoundPlayer p = new System.Media.SoundPlayer(@"C:\Media\MySoundEffect.wav");
Once we have the object, we simply invoke the Play() method thus:
p.Play();

So in two simple lines of code, we are able to play any .wav file from our application.  There are some more embedded problems that may not immediately be obvious.  Allow me to explain.

Suppose I’m trying to add the Star Trek TNG Red Alert sound to my app for an emergency notification.  I begin by locating the sound in question.  A quick web search takes me to the http://www.trekcore.com/audio/ site where the Red Alert section has several samples to choose from.  Once I locate the sound sample that I wish to use, I click the link and download the file.

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PROBLEM #1:  The file is in the .mp3 audio format.  Attempting to use it in the instantiation of the SoundPlayer() method fails with the message that only .wav files are supported.

RESOLUTION We could use a custom media player class, or we could just let the internet do some work for us.  A quick search pointed me to the http://media.io/ online audio conversion web site.  The simple interface couldn’t be cleaner or more straight forward:

image

Simply take the .mp3 file we previously downloaded and upload and convert it on this site.  Now we finally have a .wav file that we can use in our project.  Now we would like the alert sound to be played 3 times and a popup window present the error notification.  That’s easy, right?  We simply use a for() loop that looks like this:

for (int i = 0; i <= 2; i++)
{
    System.Media.SoundPlayer p = new System.Media.SoundPlayer(@"TNG-Red-Alert.wav");
    p.Play();
}
MessageBox.Show("There is an error!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);

We compile and run the app and expect the alert sound to play 3 times… only… it doesn’t.  So why doesn’t it play our audio?  It seems the problem is related to the fact that the asynchronous .Play() method, being spun from the current executing thread, does not have enough time to execute before the modal .Show() method is executed.  As you know, the MessageBox.Show() method will block the existing thread from executing any further until user action is taken on the window.  As such, the Play() method is queued really quickly given present computer CPU speeds, and once the.Show() method is invoked, it aborts the asynchronous threads to the .Play() method.  To solve the problem we have to allow the .Play() method some time to begin execution.  The easiest way to do that is to simply .Sleep() the current thread.  By injecting this line of code:

System.Threading.Thread.Sleep(1500);

right after the .Play() call, the currently executing thread will pause for 1.5 seconds.  Depending on what audio you’re playing, you can tweak this value (in milliseconds) to match accordingly.

At this point, the alert message and audio work correctly… but the OCD in me still isn’t happy with the effect we get.  When the error condition is generated, the audio alert is played three times, per our code, and then the error alert is popped up.  The problem I have with that is that the audio warning gets my attention, but then I have to wait for it to finish playing three times before the error message with useful information pops up.  That should be easy to fix, right?  Why not just simply move the .Show() method call to before the for() loop containing the .Play() call?

Unfortunately, this doesn’t work as you’d expect.  Because of the fact that the .Show() call actually freezes the current thread, the message box is displayed and then awaits user interaction before it allows the audio code to execute.  What we need is for the .Show() code to be spun off in another thread so as to allow the audio alert to play while the message is displayed.  To do this, we create a new method thus:

public void ShowAlert()
{
    System.Threading.Thread t = new System.Threading.Thread(() =>
    {
        MessageBox.Show("There is an error!", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
    });
    t.Start();
}

Once we have the message box contained in a separate thread, we simply make that call prior to playing our audio thus:

ShowAlert();
for (int i = 0; i <= 2; i++)
{
    System.Media.SoundPlayer p = new System.Media.SoundPlayer(@"TNG-Red-Alert.wav");
    p.Play();
    System.Threading.Thread.Sleep(1500);
}

Once the user interacts with the message box, the thread (t) will terminate gracefully.  In the mean time our main app is free to continue execution of our loop to play the alert sound.



Cheers
C




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