.NET, Archive, Software Design

Software Design Tip of the Fortnight: Tip #2

Jason / December 20, 2008

For this second installment of Software Design Tip of the Fortnight I want to talk a little about exceptions. Exceptions in .NET provide an excellent means of handling errors. We all know not to use exceptions for flow control, but there are many other ways to abuse exceptions.

Abusing exceptions can be anything from throwing the base Exception class, to throwing more than just exceptions. But the most common abuse of exception handling is to simply suppress them. We have all seen applications that do something similar to:

SomeBusinessObject bo = SomeBusinessObject.LoadWithId(4);
    bo.SomeIntValue = int.Parse(txtSomeTextField.Text);
   //the value wasn't int... so ignore it.

The problem with suppressing exceptions is that most components don’t just throw them for the fun of it, there is some underlying reason why the exception was thrown in the first place.

The above example appears innocent enough. Int32’s Parse method throws an exception if it cannot parse the input string. But what if in the future another developer decides that the business object’s SomeIntValue needs a certain business rules that limits the acceptable values.

public class SomeBusinessObject{ //other class code public int SomeIntValue{ get{ return _someIntValue; } set{ if(value < 0) throw new BusinessRuleException("Invalid value for SomeIntValue."); _someIntValue = value; } } } read more

.NET, Archive, C#

.NET Extension Methods

Jason / December 1, 2008

Starting in .NET 3.5 is a feature called extension methods. Extension methods allow developers to extend classes with their own instance methods. This is a concept often called mix-ins in other languages. read more

.NET, Archive, Visual Studio

Acquiring a Public Key Before Compiling

Jason / November 17, 2008

In the past I have talked about the The Wonders Of InternalsVisibleTo and how such a simple attribute allows for internal components to be shared between different assemblies, opening the door to greater code separation and dependency control. In that previous article I illustrated how you can use the tool that ships with Visual Studio to get the public key signature from one of your existing dlls. read more

.NET, Archive, Software Design

A Generic Error Occurred in GDI+

Jason / October 14, 2008

You know you’re doing good when your application crashes with an exception as detailed as “a generic error occurred in gdi+”. That is about as, well generic, as it gets :- )

In my particular case I was constructing an Image down in my DAO using the FromStream method, like so:

Image result;
using (FileStream file = File.OpenRead(filename)) {
	result = Image.FromStream(file);
return result;

I was doing this so that I could know for a fact that the file was being disposed of properly. I didn’t want to have any orphaned file references locking up the file in case I later needed to delete it.

The problem was that up in my UI I was attempting to call the Save method on Image to dump its contents out to the ASP.NET response stream, like so:

img.Save(HttpContext.Response.OutputStream, ImageFormat.Jpeg); read more

.NET, Archive, C#

Silverlight Progress Bar

Jason / October 13, 2008

Silverlight 2 provides an attractive platform for creating Rich Internet Applications, however when first getting started both the oddities of the layout model and the strange absence of certain controls and class and be puzzling.

One such puzzling absence from the Silverlight tool chest is a progress bar control. WPF has a progress bar, WinForms has a progress bar, but not Silverlight. Fortunately implementing one is not that hard and provided a great introduction to Silverlight’s layout model.

Silverlight and layers

Unlike ASP.NET, and many other forms technologies, Silverlight uses a multiple layer positioning system. The Canvas control is especially useful for allowing multiple controls to be layered.

Take for example this simple block of XAML:

<Canvas x:Name="LayoutRoot" Background="WhiteSmoke"> <Rectangle Width="60" Height="60" Fill="Green" /> <Rectangle Width="60" Height="60" Fill="Gray" /> <Rectangle Width="60" Height="60" Fill="LightBlue" /> </Canvas> read more

.NET, Archive, ASP.NET, aspNETserve, C#

Community Coding Contest

Jason / October 1, 2008

Developing an open source project is a very rewarding experience. But sadly (as an open source developer that is) open source projects rarely get the feedback they deserve. Often the developers only hear feedback from their users when their software is broken, because of this it is often difficult to know when an author’s work is truly appreciated. read more