Introduction to Sample Data - Page 5
       by kirupa  |  3 May 2010

In the previous page, you added an Image property to your sample data Collection and applied it to your ListBox to show images along with the Lorem Ipsum text and the price. In this page, we'll wrap things up by looking at how sample data makes it from the farm to your grill and revisit why you had to do some of the things you did.

A Closer Look at Sample Data
Up until now, thanks largely to me, you only have a spotted understanding of how sample data works. You use the Data panel to create a new sample data source, define some properties, and then drag the Collection field to your artboard to create a new ListBox with sample data values displayed. To tweak what your sample data contains, you go back to the Data panel, make some changes, and reapply the Collection.

The previous steps loosely summarize what you did in the first four pages, but none of the steps actually help you to understand how everything works. Let's address that shortcoming right now.

So, here is what your Data panel looks like:

[ what your data strucutre looks like right now ]

The top-most node defines the name of your sample data source, the container that defines your sample data. Below that node, you see all of the little things like the individual properties that make up everything else.

These properties help define the schema (aka the structure) your data takes. When you have three properties under the Collection node of type String, String, and Image, what you are saying is that you want a collection of sample data that contains strings and an image.

When you drag and drop the Collection onto your artboard, Expression Blend uses the properties and any customizations you made as a template for the data it will generate:

[ Blend simply takes your wishes and generates a boatload of sample data ]

There is no magic behind all of this. If you look in your Projects panel, you will see a folder created for you called SampleData. Keep expanding it until you hit some XSD and XAML/CS files:

[ your sample data is stored as loose files ]

It is these files that define the schema for your data and the actual data itself. If you open your XAML file (SampleDataSource.xaml) , you will see the sample data that you see in your ListBox displayed in the form:

<SampleData:SampleDataSource.Collection>
  <SampleData:Item Property1="..." Property2="..." Property3="..." />
  <SampleData:Item Property1="..." Property2="..." Property3="..." />
      .
      .
      .
  <SampleData:Item Property1="..." Property2="..." Property3="..." />
</SampleData:SampleDataSource.Collection>

In the equivalent C# file (SampleDataSource.cs), you will see the backing code that actually associates the XAML types to the CLR properties:

private string _Property1 = string.Empty;
 
public string Property1
{
get
{
return this._Property1;
}
 
set
{
if (this._Property1 != value)
{
this._Property1 = value;
this.OnPropertyChanged("Property1");
}
}
}
 
private string _Property2 = string.Empty;
 
public string Property2
{
get
{
return this._Property2;
}
 
set
{
if (this._Property2 != value)
{
this._Property2 = value;
this.OnPropertyChanged("Property2");
}
}
}
 
private System.Windows.Media.ImageSource _Property3 = null;
 
public System.Windows.Media.ImageSource Property3
{
get
{
return this._Property3;
}
 
set
{
if (this._Property3 != value)
{
this._Property3 = value;
this.OnPropertyChanged("Property3");
}
}
}

The lines I highlighted in yellow define the Property and the Type of the property such as String or Image (System.Windows.Media.ImageSource).

Whenever you modify anything via the Data panel that is sample data related, code in the files seen here gets modified or even regenerated to provide Expression Blend with up-to-date visuals that you can see at both design time and (optionally) at run time.

Conclusion
Well, this concludes this little article that hopefully provided you with an introduction to the really cool sample data functionality found in Expression Blend. Sample data solves a very common problem that designers face when working with modern applications, and that is being able to design and visualize data that may not actually exist outside of a finished, running application.

Because this article was an introduction, some of the more interesting sample data features beyond collections and simple properties were not covered, but subsequent articles will hopefully fill in that gap.

If you are curious to see the source code for the example shown on the first page, go ahead and download it from below:

Download Source Files

Got a question or just want to chat? Comment below or drop by our forums (they are actually the same thing!) where a bunch of the friendliest people you'll ever run into will be happy to help you out!

When Kirupa isn’t busy writing about himself in 3rd person, he is practicing social distancing…even on his Twitter, Facebook, and LinkedIn profiles.

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