Expanding on an article I wrote a couple of years ago where I explained interfaces in C#, I’d like to explain why people should use interfaces. I received an email from a reader of my ASP Alliance article. He understands how interfaces work, but he’s trying to see why so many people are raving wildly about their greatness. His questioning of them is great, because it really is not obvious why interfaces are useful. Anyone who says otherwise is just trying to brag.
A couple of years ago, you wrote an article for ASP Alliance called "Understanding Interfaces." Once again, I saw how the code works, once again, I failed to see how it will benefit me.
Here's where everything breaks down for me: You create an interface with just method, property and event signatures. Then you inherit them in a class, recreate these same signatures and write the code to implement these methods and properties.
So I’ll start by mentioning that nearly all patterns, practices, principles, etc. in software development are based on code reuse. One of the most important reasons for code reuse is change. Developers are always responding to and creating changes. We must mitigate the risks of change, identify where changes will occur, and we must make changes.
Right about now you might be thinking, “but interfaces don’t reuse code. They just force you to implement new code. Using inheritance would be the way to achieve code reuse.” You ate technically correct. You understand how interfaces work, but you’re not seeing why we use interfaces. Interfaces themselves do not give us code reuse at all, however, they enable us to achieve code reuse.
Remember that I said that we must identify where changes will occur. Making this identification allows us to isolate changes thus mitigating the risks of changes and allowing us to make changes. Isolating the places that change also allow us the reuse the code which does not change, so by keeping some parts separate we can reuse others. The interfaces are for the places we can’t reuse the code.
Interfaces are “places of change”. Each implementation of the interface is a variation on how that required piece of the puzzle could have been implemented. This is contrary to how you’ll see a lot of interfaces used. It is sometimes difficult to see this as the behavior of interfaces, because people overuse interfaces.
As I see it, I could have saved a whole lot of time by not creating the interface in the first place! I mean, it's not doing any work. I still have to create the signatures in the class. Why on Earth do people praise these things and call them the answer to multiple inheritence? They don't do anything!
It is mostly true that interfaces don’t do anything. As far as being executable code is concerned an interface is basically just a worthless extra step, so why would we use them? Declaring an interface is like saying, “there is more than one way that this behavior could be implemented, but interactions with this behavior should be done this way only.” Having that common “interface” allows us to use any of these implementations interchangeably.
When to Use Interfaces
Some people would recommend that interfaces should be used everywhere. I’ve heard people say that no variable should be declared with a concrete type if it can be avoided. That may be a valid point, but if you’re just learning how interfaces can be useful that is a bad approach. If you don’t see value in interfaces, you will certainly not see the value of them when people use them everywhere. This washes them out and obfuscates their purpose.
Interfaces are used for logic which will have multiple or changing implementations. This means that we should use them in places where we will out of necessity have duplicate logic. Using the interface is what allows us to do this. Take a look at this code for composing a letter.
public string ComposeLetter(string recipientName,
string messageBody, bool isFormal)
{
string messageText = string.Empty;
if (isFormal)
{
messageText += GetFormalGreeting(recipientName);
}
else
{
messageText += GetCasualGreeting(recipientName);
}
messageText += messageBody;
if (isFormal)
{
messageText += GetFormalSignature();
}
else
{
messageText += GetCasualSignature();
}
return messageText;
}
Notice how we have these flow control operators dictating how the code will execute. What will happen if we need to have a third option for greetings and signatures for family members? We might add another else-if or we might use a switch. Either way this code gets larger and changed every time.
However, if we identify the aspects of the code that are changing we can isolate them and mitigate the risks of changing the code by keeping separate the logic which has multiple implementations. Notice we have already used one form of encapsulation by keeping each of those pieces of logic in separate methods. The logic we haven’t encapsulated is the flow control.
We can create an interface for it. The best name I’ve got for now is IFormalityGenerator, which is not a great name, but it will do for now. I’ll create that interface with two methods: GetGreeting and GetSignature. Very simple interface. Now we can rewrite our method to look like this.
public string ComposeLetter(string recipientName, string messageBody,
IFormalityGenerator formalityGenerator)
{
string messageText = string.Empty;
messageText += formalityGenerator.GetGreeting(recipientName);
messageText += GetMessageBody();
messageText += formalityGenerator.GetSignature();
return messageText;
}
We now just make the decision sooner and only once which implementation we are using. If this is a formal letter we will use the FormalFormalityGenerator. If it is casual we will use the CasualFormalityGenerator. Down the road when we create one for family members we can just go and create an implementation for the FamilyFormalityGenerator. We’ve made it so we create new code each time instead of going and changing the existing code in this method.
The power of an interface is in its ability to encapsulate the volatile aspects of a program and isolate that which can be reused more easily.
A few days ago Jeff Atwood wrote a great post about users. This is my post adding to his.
I also develop applications, and user interfaces is a common topic of discussion. The interface of an application is one of the most important aspects of it. What a lot of people seem not to realize and Jeff nicely highlights is that users don’t read anything. Trust me. I use a lot of applications, and I avoid reading anything that is more than six or seven letters long.
If I have to read something to use an application you’re probably going to lose me. I am not here to learn your application I am here to use your application. Jeff shows this image as what a user sees on Stack Overflow when writing a question.
I think he is a little bit off here. Why? Oh I don’t know, because he includes the preview. I might look at the preview, but only if I am concerned about how something is formatted. If I don’t think I did anything complicated I don’t bother checking the preview. I figure I should be able to use this page while only really reading this section.
When I need to reference something I will find it on the page. However, the 90% case is going to be this. I’ll make a decision if I need to look elsewhere, and I’ll be annoyed when I have to.
I use Stack Overflow and I think the interface is great Jeff. You support standard keyboard shortcuts, so I can learn what they do and how to format them by only observing the editor and occasionally the preview section. When I need a list I know to use the buttons at the top. Anything that is a standard convention I will follow. You give me a toolbar of choices and keyboard shortcuts and I’m set.
I think it is most important to follow common practice if you want things right. I am not sure why people have such trouble with Stack Overflow’s editor.
The default layout for a RadChart works for most situations. It has a ChartArea, a ChartLegend, and a ChartTitle. These are easy to work with, and if you want you can break from the norm and create your own custom Silverlight Rad Chart layout. If you’re sticking with the default you almost certainly have some settings and properties to which you will want to make adjustments. In order to do that you might define these in the XAML.
<UserControl x:Class="MyApplication.UI.Charts.SuperSweetChart"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:telerikChart="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Charting"
xmlns:chart="clr-namespace:Telerik.Windows.Controls.Charting;assembly=Telerik.Windows.Controls.Charting"
Width="400" Height="300">
<Grid x:Name="LayoutRoot" Background="White">
<telerikChart:RadChart x:Name="Chart1"
Loaded="Chart1_Loaded">
<telerikChart:RadChart.DefaultView>
<chart:ChartDefaultView>
<chart:ChartDefaultView.ChartArea>
<chart:ChartArea LegendName="CustomLegend" NoDataString="">
<chart:ChartArea.DataSeries>
<chart:DataSeries x:Name="DataSeries1" >
<chart:DataSeries.Definition>
<chart:PieSeriesDefinition
LabelOffset="0.6d"
ShowItemToolTips="True"
ItemToolTipFormat = "#XCAT"
DefaultLabelFormat = "#%{p0}" />
</chart:DataSeries.Definition>
<chart:DataPoint YValue="35" />
<chart:DataPoint YValue="15" />
<chart:DataPoint YValue="55" />
</chart:DataSeries>
</chart:ChartArea.DataSeries>
</chart:ChartArea>
</chart:ChartDefaultView.ChartArea>
<chart:ChartDefaultView.ChartLegend>
<chart:ChartLegend x:Name="CustomLegend"
UseAutoGeneratedItems="True" />
</chart:ChartDefaultView.ChartLegend>
<chart:ChartDefaultView.ChartTitle>
<chart:ChartTitle>
<TextBlock Text="Traffic Sources"/>
</chart:ChartTitle>
</chart:ChartDefaultView.ChartTitle>
</chart:ChartDefaultView>
</telerikChart:RadChart.DefaultView>
</telerikChart:RadChart>
</Grid>
Notice the three parts are the ChartArea, the ChartLegend, and the ChartTitle. Use the properties of these to make your adjustments. If you don’t want to change these in the XAML then don’t include them. If you’re going to work from the code behind it doesn’t hurt to have these here, but it can be useful.
You can access these in the code behind by either declaring their x:Name property or by referencing them from the RadChart’s x:Name like this. Chart1.DefaultView.ChartArea.
Plus keeping things in here keeps designers happy, and we design-challenged people really appreciate happy designers willing to assist us.
Working with a foreach loop is the primary reason to implement the IEnumerable and IEnumerator interfaces. You’ll want one of each of these to work with the loop.
I am going to do an example DateRange class which will implement IEnumerable<DateTime> and will allow us to iterate through a non-existent collection of DateTime objects.
Note: I am aware of the fact that I could achieve the same result with a for loop. I find the foreach loop more readable.
First we need to create a basic DateRange class. A range can be defined as a StartDate and an EndDate, so I’ll start there.
public class DateRange
{
public DateRange(DateTime startDate, DateTime endDate)
{
StartDate = startDate;
EndDate = endDate;
}
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
}
So this DateRange could be useful on its own, but we want to be able to iterate this collection using a foreach. So to start we need to implement the IEnumerable<DateTime> interface.
public class DateRange : IEnumerable<DateTime>
{
public DateRange(DateTime startDate, DateTime endDate)
{
StartDate = startDate;
EndDate = endDate;
}
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
public IEnumerator<DateTime> GetEnumerator()
{
return new DateRangeEnumerator(this);
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
Notice here that we now need to get the IEnumerator<DateTime> object in the GetEnumerator() method. I jumped the gun a bit and I’ve called a class that doesn’t exist yet. I’ll make another class and implement the required methods for the IEnumerator interface.
public class DateRangeEnumerator : IEnumerator<DateTime>
{
private int _index = -1;
private readonly DateRange _dateRange;
public DateRangeEnumerator(DateRange dateRange)
{
_dateRange = dateRange;
}
public void Dispose()
{
}
public bool MoveNext()
{
_index++;
if (_index > (_dateRange.EndDate - _dateRange.StartDate).Days)
return false;
return true;
}
public void Reset()
{
_index = -1;
}
public DateTime Current
{
get { return _dateRange.StartDate.AddDays(_index); }
}
object IEnumerator.Current
{
get { return Current; }
}
}
These are the handful of methods we implement for the IEnumerator<DateTime> interface. These are all about moving to the next object and getting the current object. Resetting and Disposal of the object are less important, so make sure you read MoveNext and Current.
Keep in mind here that I could have used a collection for this, but I didn’t because I don’t need one. The calculation to get the items was easy enough.
var dateRange = new DateRange(DateTime.Today.AddDays(-6), DateTime.Today);
foreach (DateTime date in dateRange)
{
Console.WriteLine(date.ToShortDateString());
}
Output:
10/20/2009
10/21/2009
10/22/2009
10/23/2009
10/24/2009
10/25/2009
10/26/2009
As of today Visual Studio Beta 2 is available to the general public. There is a VS 2010 Beta 2 iso available for download. It has some really nifty features. I’ve been playing around with it.
First off I will say that it actually looks very cool.
I think they did well. The new start page here is also a lot cleaner. I’ll be looking to see how to customize it a little.
Creating new projects is a lot better. Far less intimidating in this new default view. If they can keep the clutter down on this I will be very happy.
So I created an “Empty ASP.NET Web Application”. I noticed one crazy thing about it. I don’t think there are enough references here? Maybe we need more. C’mon guys. Seriously. Who wants to start with all of these in there? I chose the “Empty” one so I wouldn’t have all of this clutter.
But wait! They did remove the clutter. Guthrie had mentioned they were doing this. I am just now seeing the web.config and it is AWESOME!
There is barely anything in the web.config. Yipee! Hooray!
“Navigate To” is a nice feature. I already use ReSharper, so the wow factor is gone. I am glad to have it integrated though.
We were able to move the editor window around in previous versions of Visual Studio, but this feels a lot nicer, and anyway it’s still useful. Grab an editor window and decide where to put it. Much more freedom for splitting the screen this way.
You can do stuff like this. And have three editors open at once (you better have a lot of screen real estate before you try this).
Or if you actually use the designer in Visual Studio you can split it along with the code behind file. Getting you the Design, Source, and Code Behind.
This looks like a pretty nice thing they’ve build here. I figured with the big changes they were making that this version of VS would be lacking in too many upgrades. It seems they’ve managed to pull off some nice stuff here.
I am sure I’ll discover more new stuff at some point. Luckily the same feel is here, so just need to learn all of the little changes and additions.
