Programming XAML - A Quick Start

Mahesh Chand
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XAML is a new descriptive programming language developed by Microsoft to write user interfaces for Windows 8 metro style apps, WPF and Silverlight applications. This article is a basic introduction to XAML.

The Root Element

The root element of the XAML must have namespace defined as following:

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/
presentation

The root element of an XAML document can contain only certain elements and these elements are a Window, a Canvas, or panels. XAML has different types of panels used for different purposes. I will be talking about panels in more details in my forthcoming articles.

Windows and Canvas

Once the root element is defined, children are defined within the root element. For example, the following XAML code creates a Window and a Button as the child of the window.

<Button>Hello World</Button>

</Window>

The <Window> element represents a window, which replaces a Windows Form or ASP.NET Web page in previous Microsoft development platforms and the <Button> element represents a button control.

The above code generates the following output:

Image 1. A Window generated using XAML

Here is another example. In this example, I use <Canvas> element as the root element. Again, a canvas can be treated as a parent control of other child controls.

<Button>XAML Button</Button>

</Canvas>

The above code generates output as Figure 2. As you can see from Figure 2, an XAML document is rendered directly by the browser.

Figure 2. Button control

XAML Control Attributes

Each of the elements such as <Window> or <Button> has attributes and can be set within the element itself. For example, a Button has Height, Width, Background, Foreground and other attributes, which represents height, width, foreground color, and background color of the button respectively.

The following code snippet sets the Id, height, width, background color, foreground color, font name and size, and content of a button. The Content attribute represents the text of the botton.

Figure 3 is the result of above code. As you can see from Figure 2, the button has white foreground and red background, with the size specified in the code.

Figure 3. Button with red background.

Like any other controls, you can also define the events of the controls within the XAML element itself. For example, the Click attribute of the <Button> represents the click event handler of the button. The following code sets the Click attribute of the button as ButtonClickMethod, which means when the button is clicked; the code written on the ButtonClickMethod will be executed.

<Button Name="btn1" Height="50" Width="200" Background="Red" Foreground="White"

FontFamily="Times New Roman" FontSize="14" Content="Red Button" Click="ButtonClickMethod"/>

Control Event Handlers

Now lets define the ButtonClickMethod. I am using C# language. The code is always written within <![CDATA[ ]]> element. My ButtonClickMethod is listed in Listing 5. As you can see from Listing 5, I can also set the button's properties at run-time in my code as well. I also generate a message box when the button is clicked.

<![CDATA[

void ButtonClickMethod(object sender, EventArgs e)

{

btn1.Background = Brushes.Green;

MessageBox.Show("Red Button clicked");

}

]]>

The final code is listed in Listing 6.

<Button Name="btn1" Height="50" Width="200" Background="Red" Foreground="White"

FontFamily="Times New Roman" FontSize="14" Content="Red Button" Click="ButtonClickMethod"/>
<x:Code>

<![CDATA[

void ButtonClickMethod(object sender, EventArgs e)

{

btn1.Background = Brushes.Green;

MessageBox.Show("Red Button clicked");

}

]]>
</x:Code>

</DockPanel>

The output of Listing 6 generates Figure 4. As you can see from this Figure, when you click on the button, it changes the color of the button to green and generates a message box saying "Red Button clicked".

Figure 4. Button click output

Communication between two Controls

Now let's create one Windows application with a TextBox and a Button control on it. In this application, we will change the TextBox.Text property on button click event. Our final Window looks like Figure 5.

Figure 5. A Window with a TextBox and a Button control

The code for creating a Windows, a TextBox, and a Button is listed in Listing 7. In this code, the <Window /> element represents a Window.

<Window x:Class="WindowsApplication5.Window1"

xmlns="http://schemas.microsoft.com/winfx/avalon/2005"

xmlns:x="http://schemas.microsoft.com/winfx/xaml/2005"

Title="WindowsApplication5"

<Button VerticalAlignment="Top" HorizontalAlignment="Left" Grid.Column="0" Grid.ColumnSpan="1" Grid.Row="0" Grid.RowSpan="1" Margin="232,99.5,0,0" Width="135" Height="55" Name="button1" Click="ButtonClickMethod">Button</Button>

</Grid>

</Window>

Listing 8.

Now let's add code to change Text property of TextBox as listed in Listing 8. This code should look familiar. On button click event handler, we are simply setting textBox1.Text to "Button clicked" string.

<x:Code>
<![CDATA[

void ButtonClickMethod(object sender, EventArgs e)

{

textBox1.Text = "Button clicked";

}

]]>

</x:Code>

Listing 9.

Now let's run the application and click on the button. The output looks like Figure 6.

Figure 6.

In-line versus Code-behind

Similar to ASP.NET programming model, we have choice to write code in XAML document itself or in a seperate file as code-behind. In our previous example, we used the following syntax to write in-line code.

<![CDATA[

However, you have choice to use a seperate file and place all code in that file as code-behind file. If you want to do so, you have to tell your XAML document the file name using the following syntax.

In the above code, the code-behind code is placed in XamlNotePad.Window1 class. The in-line code is compiled at run-time but if you have a code-behind file, you will have to compile the application before deploying it.

This is why XAML is HOT!

I did lot of work with graphics using GDI+ and graphics objects such as Rectangle, Ellipse, Line, and Path did not have any events.

Guess what? All of these objects in XAML have events now. In other words, I can have a mouse down event on an ellipse. That's pretty cool.

The following code creates an Ellipse and adds MouseDown event handler called EllipseMouseDown. I have EllipseMouseDown defined in code-behind.

Here is the MouseDown event handler in .cs file.

void EllipseMouseDown(object sender, MouseButtonEventArgs e)
{
MessageBox.Show("Mouse was down");
}

Now when you mouse down on the ellipse, the output looks like Figure 7.

Figure 7.

Pretty cool. huh?

Summary

This article is a basic introduction to XAML. In this article, you saw how to create simple user interfaces and controls using XAML. You also learnt how we can create controls and write event handlers for the controls.

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