introduction

in this article, i will show you how to create a program that checks whether the links in your web application are active or not. we will use internet transfer control to accomplish this task. this is a real world example where you will see the real use of internet transfer control.

about the application

internet transfer control is a very handy control. the program will check each link in the web page to see if it's functioning or not. suppose, i add web page addresses of different people on my web page. now, the web pages usually move to different locations or people simply put their sites off the internet, and all of a sudden my links are dead. if i have more than 100 links on my page, then to check all those pages manually will be a hectic task and we can't check the urls on a regular basis. so, we need to automate this process. an easy way is to keep a links database either in access or in excel and then check all the links in the database whether they are functioning. you can populate your web page with the live links from your database.

what this program does?

the program we are going to create will perform the following tasks:

1. the program would open a worksheet.
2. it would use ole automation to read the first url and see whether it's functioning.
3. write data back to the worksheet, indicating the result for the url.
4. repeat the preceding steps for all the urls in the list.
5. save and close the worksheet.

what is ole?

ole stands for object linking and embedding. it is a technology for transferring and sharing information among applications. different applications expose their objects that are related to the kind of data the application works with. automation client is an application that expose objects belonging to another application. in our case, our vb program will act as an automation client. an automation server is an application that exposes programmable objects to other applications. in our case, excel will act as an automation server. excel exposes automation objects. these objects have properties and methods as their external interface. properties are named attributes of the automation object. methods are functions that work on an automation object.

more about the application

let's discuss the layout of the excel worksheet where the data will be stored. when the program has completed the task, each record in the excel worksheet will contain an entry specifying the current status of the url. the application will run minimized in the background while your other applications work normally. the number of links already checked is displayed in the program's title bar and therefore also displayed on the taskbar icon when the program is minimized. this enables the user to keep track of the progress. when the urls have been checked, the program closes the worksheet and displays a summary report.

url will be saved in column c, the third cell from the left, and the information as to whether the link is okay is kept in column e. data begins in row 4.

i have included detailed comments in the code so that you can see how it works. you will have to edit the code before running it. change the path of the excel file in the code.

'save the filename in a variable


const file = "c:\hrd_links.xls" 
'(this variable should contain the exact path of the file)

here is the complete code of the application:

'create the excel object


set objexcel = createobject("excel.application")

'open the worksheet

objexcel.workbooks.open myfile

'set the transfer protocol

inet1.protocol = ichttp

'this is the main function!!

public sub check_links()

'this function will be called to check all the links in the

'worksheet.


'declare variables

dim var_row as integer
dim var_url as string
dim var_buffer as string
dim var_msg as string
dim var_file_not_found as integer
dim var_server_not_found as integer
dim var_timeout as integer
dim var_ok as integer

'catch the time-out errors


on error resume next

'set the row variable to the cell where the data starts

var_row = startrow

'initialize the variables


var_timeout = 0
var_file_not_found = 0
var_ok = 0
var_server_not_found = 0


'minimize the form

frmmain.windowstate = 1


'loop through all the urls

do
    'get the url

    var_url = objexcel.cells(var_row, url_col)

    'check whether the first cell is empty

    if var_url = "" then exit do

    'open the url

    text1.text = inet1.openurl(var_url)

    'avoid tying up the system

    doevents

    'errors messages are found in the  first 50 characters

    'returned by the openurl method


    if len(text1.text) > 50 then

        var_buffer = left(text1.text, 50)

    else

        var_buffer = text1.text

    end if

    'catch a time-out error


    if err = 35761 then
         var_msg = "timed out"
         var_timeout = var_timeout + 1
    err.clear

    'if nothing is returned, it means that the server was

        'not found


    elseif text1.text = "" then

        var_msg = "server not found"
        var_server_not_found = var_server_not_found + 1

        'if error 404 is returned from the url, it means the

       'server was found but he file was not found


    elseif instr(1, var_buffer, "404") then

        var_msg = "file not found"
       var_file_not_found = var_file_not_found + 1

    'else, the link is ok


    else

        var_msg = "ok"
        var_ok = var_ok + 1

    end if

    'save the result back to the worksheet


    objexcel.cells(var_row, status) = var_msg

    'move to the next row


    var_row = var_row + 1

    'display the current status.


    frmmain.caption = var_ok + var_file_not_found + _ 
                            var_server_not_found + var_timeout

    'display the results on the form


    label1.caption = "ok: " & var_ok
    label2.caption = "file not found: " & var_file_not_found
    label3.caption = "server not found: " & var_server_not_found
    label4.caption = "timed out: " & var_timeout

loop while true

'if all the links have been checked, restore the form


frmmain.windowstate = 0

'close the worksheet


objexcel.workbooks.close

'remove the object from the memory

set objexcel = nothing

'display the results


var_buffer = "ok: " & var_ok & vbcrlf
var_buffer = var_buffer & "server not found: " & _ 
                       var_server_not_found & vbcrlf
var_buffer = var_buffer & "file not found: " & _ 
                       var_file_not_found & vbcrlf
var_buffer = var_buffer & "timed out: " & var_timeout

msgbox var_buffer

open the excel workbook and add the links you want the program to check. close the workbook and run the program. make sure you are connected to the internet. that's it.