How to Validate a TextBox Control in F#

Introduction

This article shows how to validate a user control in a Windows Forms form.

Step 1:

Open Visual Studio then select "Create New Project" --> "F# Console Application".

Step 2:

Now go the Solution Explorer on to the right side of the application. Right-click on "References" and select "Add references".

Step 3:

After selecting "Add References", in the framwork template you need to select "System.Windows.Forms" and "System.Drawing" while holding down the Ctrl key and Click on "Ok." 

Step 4:

Write the following code in the F# editor:

// Learn more about F# at http://fsharp.net

open System.Collections.Generic

open System

open System.Windows.Forms

open System.ComponentModel

open System.Drawing

let validform = new Form(Text="Validate Inputs",AutoScaleDimensions=new System.Drawing.SizeF(60.0F, 13.0F),ClientSize=new System.Drawing.Size(300, 200),StartPosition=FormStartPosition.CenterScreen)

let exitbutton=new Button(Text="Exit", Location=new System.Drawing.Point(190, 170))  

let okbutton=new Button(Text="Ok", Location=new System.Drawing.Point(100, 170)) 

let lblname=new Label(Text="Enter a name:",Location=new System.Drawing.Point(0, 10),AutoSize=true)

let lname=new Label(Text="Enter Last name:",Location=new System.Drawing.Point(0, 50),AutoSize=true)

let nametxtbox=new TextBox(Location=new System.Drawing.Point(120,10),BorderStyle=BorderStyle.FixedSingle)

let lnametxtbox=new TextBox(Location=new System.Drawing.Point(120,50),BorderStyle=BorderStyle.FixedSingle)

validform.Controls.Add(exitbutton)

validform.Controls.Add(okbutton)

validform.Controls.Add(lblname)

validform.Controls.Add(lname)

validform.Controls.Add(nametxtbox)

validform.Controls.Add(lnametxtbox)

okbutton.Click.Add(fun ok->

if(nametxtbox.Text="" || lnametxtbox.Text="")then

 MessageBox.Show("Fields can not be empty","Validate Inputs",MessageBoxButtons.OK, MessageBoxIcon.Information)|>ignore) 

exitbutton.Click.Add(fun exit->validform.Close())

Application.Run(validform)

Step 5:

Debug the application by pressing F5 to execute the application. After debugging the application you will get an application as in the figure below:

Step 6:

If you'll enter only name and left the field last name lastname textbox then lastname textbox validated see the figure

Step 7:

If both the fields gets empty and click on ok button then validation arises.