Learning by sample gdi+ - thumbnail

w w w . B u k a n S e m b a r a n g . I n f o © 2 0 1 1

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GDI+ : Thumbnail 2011


GDI+ : Thumbnail

Learning By Sample Series


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Foreword

Learning By Sample ?

So, why should I made this tutorial freely accessed by everyone ? Well, surely I

am just nobody, I also just another ordinary person with ordinary knowledge. However,

I always feel that some persons in the internet giving away their tutorial for free and I

feel being helped by them. Then, I remember one of my senior wisdom words : “If you

want to be given more, then start to give more”. And of course, I really believe those

words, since that I already proof it to be right all the time.

Also, I’m not an English native speaker, however, I just try to improve my

English in any other way, especially in written format. Thus, I think writing is the best

practice to improve my English freely. However, you will find many grammatical errors

in my tutorial, so please send me comments and also suggestion to improve it.

Then, why the format using Learning By Sample series ? Is it really different with

other tutorials out there ? Ehm, I already wrote three books (in Indonesian) using this

kind of format, and many readers already contact me about how this format really help

them to learn from the scratch. So, why in the world I’m not re-create it in English

format, right ? Eventhough actually, it is similar with Hands On Lab series which

already famous in Microsoft site previously.

All of my lesson also being designed as short samples and short time exercise.

Thus, I hope that each of tutorial series would take only at least 10-15 minutes

maximum to learn. Why keep it short ? Because many beginners (and even expert) will

find boring whenever they must keep studying more than 15 minutes (but you will

never get bored when you online in such time right ?).


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Another reason is just because many of samples in this series come up from my

lecturing task exercise. So, I just try to compile all my lab exercises in order to keep it

tidy and also reusable for my students. That’s why you will find many unsorted course

material inside these series, however, just take a seat and enjoy the ride !

Requirements

In this series, I try to give simple example about GDI+. So what is GDI+ anyway ?

GDI+ or GraphicsDrawing Interface is merely part of .NET Framework which entirely

purposed in manipulating graphics. However I’m not going to make you understand

complex theory about this class. I just try to make you understand it in very simple and

stupid way.

All of my samples in this series use Visual Web Developer 2010 Express edition

however you can also do it all using Visual Studio. If you really want to follow this

series, then you should aware that basic programming knowledge is needed. You

should also familiar with ASP .NET especially for version 3.5 above.

FYI, I’m a VB guy, so please don’t complaint if I use VB entirely in this series. But

nowadays, there’s no such useful things if we argue about language differences,

because I just try to share something that I know. So, if you don’t like VB and want to

have another tutorial with your own favourit language, then I’d be happy to read it.

Now, let’s get started…….


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Let’s Get Started

1. First, ensure that you already open Visual Web Developer 2010 Express Edition

2. Create a newly blank website and give it a name

3. Now, let’s create a new blank web page


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4. In newly created web page, insert new table which has 3 rows and 2 columns, by

clicking menu Table � Insert Table and in available dialog box set its rows and

columns value :


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5. Type some text just for descriptive reason in first column and a FileUpload control

in second column, both of the at first row :

6. In second row of the table, put a Button in first column and an Image control in

second column. Set the width and height property of the Image control, both with

the same size which is 50px. This Image control will be used as thumbnail

container later.


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7. In third row, put a Listbox for it first second and another Image control in next

column. In this second Image control set the width and height property to 300px,

since that this control will be the container of the real image.


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8. And int the last row, put a Label control and set its Text property to none. This

Label will be the container of some explanation text later.


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9. Now, let’s type some code for the Button, here it is :


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10. Still getting some typo errors ? Don’t worry, just add this function and procedure

below it :

11. Another error warning ? Then add this snippet at the top of Code editor :


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12. Then back to Design mode, set the only available Listbox to an autopostback

behavior. Then double click it to type the code inside :

13. The final step in the code editor is create a Page_Load event which contains this

code :


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14. And the last step is creating a folder which will hold all the uploaded images. Just

go to Solution explorer and right click in order to choose New folder and name it as

images folder.

15. Now, before you execute the web page, here is some explanations for you :

a. At first, we need two references : first for GDI+ (Drawing) and second for the

file operation (IO). File operation reference is needed for Listbox which

display all the thumbnail images in images folder.


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b. Then we also need some basic variables to declare the IO operation

c. So, what happen when we click the Button ?

i. First, of course the uploading process happen

ii. Next, we create a thumbnail from the uploaded image using

GetThumbnailImage method. We create a 100 x 100 pixel thumbnail

for any uploaded image (you can also do calculation in order to keep

the image thumbnail looks proportional), and then save it with adding

prefix thumb. As you can see, that method need a dummy function

which return true value, so we create that dummy function….


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iii. Then, the IsiList procedure being called in order to refresh the content

of Listbox. FYI, IsiList is an Indonesian phrase which means fill the

list. In this procedure we just grab all the contents in images folder

and display it in Listbox. Remember that this procedure being

executed two times, in Button click and in Page load.

d. Finally, when we already have some images uploaded, Listbox should have

some contents. Then when user click at one of those contents, we just

display the thumbnail version in first Image control, and the real one in


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second Image control. I also add an description of how the thumbnail help us

in reducing bandwidth of user by display the real size of image and compare

it with the thumbnail size.

In this procedure also you can see how I manipulate the file name string.

When all the thumbnail file name begin with thumb, it means I have to

eliminate five first lettters in order to get the real name of Image file (focus

on Mid function usage).

16. Got something in the explanation ? Or still confuse ? Maybe executing the web page

will give you some enlightment …..


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17. Ok then, I don’t need any donation for this tutorial, but I really appreciate if you

help me to spread this tutorial to others. And also, give some critics, suggestions or

any other complaints to my email : [email protected] , also don’t forget to keep

visiting my site : www.bukanSembarang.info for more tutorials. See you in next

interesting tutorial : creating your own Captcha….

Education

Learning by sample gdi+ - thumbnail