How do disable back button in browser

Generally there are cases when we want to disable back button in browser. We have multiple options to disable back button in browser. Here are the few:-

Java Script Way
We can use following java script to prevent back button:-

<script type = "text/javascript" >

function disableBackButton()

{ 

window.history.forward();

}

setTimeout("disableBackButton()", 0);

window.onunload=function()

{

null

};

</script>

HTML Way
We can also add Meta Tags in Head Section like this:-

<meta http-equiv="Pragma" content="no-cache" />

<meta http-equiv="Expires" content="-1" />

If you want to do above approach through code. Here is the trick:-

HtmlMeta pragma = new HtmlMeta();

pragma.HttpEquiv = "Pragma";

pragma.Content = "no-cache";

Page.Header.Controls.Add(pragma);

 

HtmlMeta expires = new HtmlMeta();

expires.HttpEquiv = "Expires";

expires.Content = "-1";

Page.Header.Controls.Add(expires);

ASP.Net Way
In ASP.Net we can use Cache to disable back button like this:-

Response.Cache.SetCacheability(HttpCacheability.NoCache);

Response.Cache.SetExpires(DateTime.UtcNow.AddMinutes(-1));

Response.Cache.SetNoStore();

Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);

A potentially dangerous Request.Form value was detected from the client

Above error comes because by default ASP.Net blocks the possible Script Injection request. e.g. if user type <script>alert('yes');</script> in your text box and when you display the text in text box, this java script will be executed instead of displaying text.

To resolve this problem you need to keep few things in mind:-

1- We can remove HTML Tags from TextBoxes with a simple regular expression filter like this:-

<asp:textbox id="txtSecureTextBox" runat="server" onblur="this.value = this.value.replace(/&lt;\/?[^>]+>/gi, '');">

2- Add ValidateRequest="false" in your Page directive line incase you want to disable this on single page.

<%@ Page Language="C#" AutoEventWireup="true" ValidateRequest="false"/>

3- Incase you want to disable validation through out the site then you can do it in your web.config file like this:-

<configuration>  

  <system.web>  

    <pages validateRequest="false" />  

  </system.web> 

</configuration>

4- Use HTMLEncode whenever you are displaying unsafe contents in labels like this:-

Label1.Text = Server.HtmlEncode(TextBox1.Text) 

For further details see Request Validation - Preventing Script Attacks.

Generate High quality Thumbnail Images and Maintain Aspect Ratio

I was looking up for a simple thumbnail generator through which I can generate thumbnail images. I found some code and tried to implement that but thumb images look too ugly and stretched in most of the cases. Solution to good looking thumbnail is that we have to maintain aspect ratio of actual image in our thumbnail image otherwise thumbnail will look really bad. Here is the class through which you can easily generate high quality thumbnails.

using System;

using System.Drawing;

using System.Drawing.Imaging;

namespace ConsoleApplication1

{

    public class ThumbnailGenerator

    {

        /// <summary>

        /// Generates the thumbnail of given image.

        /// </summary>

        /// <param name="actualImagePath">The actual image path.</param>

        /// <param name="thumbnailPath">The thumbnail path.</param>

        /// <param name="thumbWidth">Width of the thumb.</param>

        /// <param name="thumbHeight">Height of the thumb.</param>

        public static void Generate(string actualImagePath, string thumbnailPath, int thumbWidth, int thumbHeight)

        {

            Image orignalImage = Image.FromFile(actualImagePath);

            // Rotating image 360 degrees to discart internal thumbnail image

            orignalImage.RotateFlip(RotateFlipType.Rotate180FlipNone);

            orignalImage.RotateFlip(RotateFlipType.Rotate180FlipNone);

            // Here is the basic formula to mantain aspect ratio

            // thumbHeight   imageHeight     

            // ----------- = -----------   

            // thumbWidth    imageWidth 

            //

            // Now lets assume that image width is greater and height is less and calculate the new height

            // So as per formula given above

            int newHeight = orignalImage.Height * thumbWidth / orignalImage.Width;

            int newWidth = thumbWidth;

            // New height is greater than our thumbHeight so we need to keep height fixed and calculate the width accordingly

            if (newHeight > thumbHeight)

            {

                newWidth = orignalImage.Width * thumbHeight / orignalImage.Height;

                newHeight = thumbHeight;

            }

            //Generate a thumbnail image

            Image thumbImage = orignalImage.GetThumbnailImage(newWidth, newHeight, null, IntPtr.Zero);

            // Save resized picture

            var qualityEncoder = System.Drawing.Imaging.Encoder.Quality;

            var quality = (long)100; //Image Quality 

            var ratio = new EncoderParameter(qualityEncoder, quality);

            var codecParams = new EncoderParameters(1);

            codecParams.Param[0] = ratio;

            //Right now I am saving JPEG only you can choose other formats as well

            var codecInfo = GetEncoder(ImageFormat.Jpeg);

            thumbImage.Save(thumbnailPath, codecInfo, codecParams);

            // Dispose unnecessory objects

            orignalImage.Dispose();

            thumbImage.Dispose();

        }

        /// <summary>

        /// Gets the encoder for particulat image format.

        /// </summary>

        /// <param name="format">Image format</param>

        /// <returns></returns>

        private static ImageCodecInfo GetEncoder(ImageFormat format)

        {

            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

            foreach (ImageCodecInfo codec in codecs)

            {

                if (codec.FormatID == format.Guid)

                {

                    return codec;

                }

            }

            return null;

        }

    }

}

To use this class simply call Generate function of ThumbnailGenerator class. Here is a sample:-

ThumbnailGenerator.Generate(@"C:\images\myPicture.jpg", @"C:\images\myPictureThumb.jpg", 100, 150);

Different Server Side Tags

There are multiple types of server tags and most of the time I wonder what does they mean and in which situation what tag should I use. I Search out the internet and found something which I like to share.

There are six types of the server side tags:-

1. <% %> This is an inline server side code block which is executed during Render. Generally we call methods inside our page code behind file through this. For Details see this.
2. <%= %> This is the replacement for Response.Write to a specific place. Most of the time we use it to display single pieces of information. For Details see this.
3. <%# %> We use during the data binding. For Details see this.
4. <%$ %> This is used for ASP.NET Expression. Generally I use it to extract resources from resource files. For Details see this.
5. <%@ %> This is use for Directive Syntax. For Details see this.
6. <%-- --%> Server-Side Comments generally we use this to comment server side controls. For Details see this.

How to send periodic/timely Emails

I was busy during last few months and can not spare time for my blog. However during my project i came up with a situation that I have to send emails on daily basis through system. I would like to share the different approaches which I found during my goggling.

I came across three options to accomplish this:-

1- Create a simple .exe file which sends the mails and add it in windows scheduled tasks.
How To Schedule Task in Windows XP

2- Create a Window Service, which sleeps for 24 hours after sending emails.
Simple Windows Service Sample

3- Create a JOB in Sql Server. For details see:
Automated Email Notifications using SQL Server Job Scheduler