Web Development

Back to basics string vs StringBuilder

This is simple stuff but is something I see people easily miss by just not thinking about it.

A string is an immutable object, which means once created it can not be altered. So if you want to do a replace or append some more text to the end a new object will be created.

A StringBuilder however is a buffer of characters that can be altered without the need for a new object to be created.

In the majority of situations a string is a perfectly reasonable choice and creating an extra 1 or 2 objects when you append a couple of other strings isn't going to make a significant impact on the performance of your program. But what happens when you are using strings in a loop.

A few weeks ago one of my developers had written some code that went through a loop building up some text. It looked a little like this:

1string foo = "";
2 
3foreach (string baa in someSortOfList)
4{
5    foo += " Value for " + baa + " is: ";
6 
7    var aValue = from x in anotherList
8                 where x.name == baa
9                 select x;
10 
11    foo += aValue.FirstOrDefault().value;
12}

Everything worked apart from the fact it took 30seconds to execute!

He was searching through convinced that the linq expressions in the middle was what was taking the time, and was at the point of deciding it could not go any faster without a new approach.

I pointed out not only had he used strings rather than a StringBuilder, but the loop also created around 10 string objects within it. The loop which repeated a couple thousand times was therefore creating 20000 objects that weren't needed. After we switched froms strings to a StringBuilders the loop executed in milliseconds.

So remember when your trying to work out why your code may be slow, remember the basic stuff.

Image resizing

Using 3rd party components while essential, can also be a headache. All to often you can find yourself spending hours following the setup instructions to the letter only for it to not work. Other times you know it's the exact component you want to use but it seems while the guys may have spent a huge effort in writing to component they seemingly never got round to writing anything to tell you how to use it.

Every so often though I come across a component that works first time and does exactly what you want. One such component that I've found this with recently ImageResizer.

I needed a simple way for images to be resized for a product listing on an eCommerce platform written in Classic ASP. Image resizing can be a real pain, there's the decision of do you do it when the images are uploaded or on the fly, if you do it on the fly there's a a huge number of mistakes you can make and nearly every example of how to do image resizing includes a couple of them. Then lastly in either scenario you need to make sure the end result is actually decent quality.

With image resizer I was done in 5 minutes! It's actually a .NET component rather than Classic ASP but that wasn't an issue. You create a bin folder, add a couple of simple lines to your web.config file then put an extra extension on the image path plus parameters for the size you want and that's it!

If your doing a .NET project it's also available on NuGet making it even easier to get up and running.

Master Page Error

If you're like me you may have gone into design mode in visual studio 2010 hoping to do some work only to be greeted with the following message.

Which initially is a bit confusing, as your site may have just run without any problems. But even so you go to check the placeholders anyway and they look fine. Then you copy and paste the ID's out of the Master Page just to be sure, but still no luck. Check through the Master Page itself and that also looks fine, no squiggly lines to be seen. Finally create a new WebForm linked to the master page, but even this gives the same error.

Now if you have the problem I had, look at the title tag in the Master Page. Does it say <title /> or <title></title>? If it's the first then that's your issue. By default VS2010 will put in the correct tag, but if like me you've just slapped in some HTML from an old project or from a PSD conversion that's been done for you, then chances are you may end up overwriting the title tag as well.

.Net Tip: Default Button for Enter Key

I don't know if I should be happy to now know about this, or just concerned that it's taken me this long to discover. But one issue that surfaces time and time again when programming in ASP.NET, is that issue that pressing enter/return in a text field doesn't always do what you want it to do. 

On a normal website you can have many forms each with their own submit button which becomes the default action when pressing return on one of the forms fields. However in ASP.NET Web Forms there is only ever one form on a page, but there could be 10 different buttons each needing to be the default action for a particular text box. 

The solution as it turns out is very simple and you have two options both introduced in .NET 2.0 (yes that's how old it is!) 

1. Default button for the form. If your page has more than one button, but there is only one that you want to fire when you hit enter then in the code behind you can just type... 

1Form.DefaultButton = Button1

or it can also be specified in your aspx file 

1<form runat="server" defaultbutton="Button1">

2. If you need to be more specific a panel can also have a default button... 

1Panel1.DefaultButton = Button1
2

3<asp:Panel runat="server" DefaultButton="Button1">