Attaching a Command to the WP7 Application Bar.

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One of the biggest problems that I’ve seen with people creating WP7 applications is how do you bind the application bar to a Relay Command. If your using MVVM then this is particular important. Let’s examine the code that one might add to start with. 

<phone:PhoneApplicationPage.ApplicationBar>      <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">          <shell:ApplicationBarIconButton x:Name="appbar_button1" IconUri="/icons/appbar.questionmark.rest.png" Text="About">              <i:Interaction.Triggers>                  <i:EventTrigger EventName="Click">                      <GalaSoft_MvvmLight_Command:EventToCommand Command="{Binding DisplayAbout Mode=OneWay}" />                  </i:EventTrigger>              </i:Interaction.Triggers>            </shell:ApplicationBarIconButton>          <shell:ApplicationBar.MenuItems>              <shell:ApplicationBarMenuItem x:Name="menuItem1" Text="MenuItem 1"></shell:ApplicationBarMenuItem>              <shell:ApplicationBarMenuItem x:Name="menuItem2" Text="MenuItem 2"></shell:ApplicationBarMenuItem>          </shell:ApplicationBar.MenuItems>      </shell:ApplicationBar>  </phone:PhoneApplicationPage.ApplicationBar>

Everything looks right. But we quickly notice that we have a squiggly line under our Interaction.Triggers. The problem is that the object is not a FrameworkObject. This same code would have worked perfect if this were a normal button.

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OK. Point has been proved. Let’s make the ApplicationBar support Commands. So go ahead and create a new project using MVVM Light. If you want to check out the source and work along side this tutorial then click here

7 Easy Steps to have binding on the Application Bar using MVVM Light (I might add that you don’t have to use MVVM Light to get this functionality I just prefer it.)

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1) Download MVVM Light if you don’t already have it and install the project templates. It is available at http://mvvmlight.codeplex.com/.

2) Click File-New Project and navigate to Silverlight for Windows Phone. Make sure you use the MVVM Light (WP7) Template.

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3) Now that we have our project setup and ready to go let’s download a wrapper created by Nicolas Humann here it is called Phone7.Fx. After you download it then extract it somewhere that you can find it. This wrapper will make our application bar/menu item bindable.

4) Right click References inside your WP7 project and add the .dll file to your project.

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5) In your MainPage.xaml you will need to add the proper namespace to it. Don’t forget to build your project afterwards.

xmlns:Preview="clr-namespace:Phone7.Fx.Preview;assembly=Phone7.Fx.Preview" 

6) Now you can add the BindableAppBar to your MainPage.xaml with a few lines of code. 

<Preview:BindableApplicationBar x:Name="AppBar" BarOpacity="1.0"  >      <Preview:BindableApplicationBarIconButton Command="{Binding DisplayAbout}" IconUri="/icons/appbar.questionmark.rest.png" Text="About" />      <Preview:BindableApplicationBar.MenuItems>          <Preview:BindableApplicationBarMenuItem  Text="Settings" Command="{Binding InputBox}" />      </Preview:BindableApplicationBar.MenuItems>  </Preview:BindableApplicationBar>
So your final MainPage.xaml will look similar to this: NOTE: The AppBar will be located inside of the Grid using this wrapper.  
<!--LayoutRoot contains the root grid where all other page content is placed-->  <Grid x:Name="LayoutRoot"        Background="Transparent">      <Grid.RowDefinitions>          <RowDefinition Height="Auto" />          <RowDefinition Height="*" />      </Grid.RowDefinitions>        <!--TitlePanel contains the name of the application and page title-->      <StackPanel x:Name="TitlePanel"                  Grid.Row="0"                  Margin="2424012">          <TextBlock x:Name="ApplicationTitle"                     Text="{Binding ApplicationTitle}"                     Style="{StaticResource PhoneTextNormalStyle}" />          <TextBlock x:Name="PageTitle"                     Text="{Binding PageName}"                     Margin="-3-800"                     Style="{StaticResource PhoneTextTitle1Style}" />      </StackPanel>        <!--ContentPanel - place additional content here-->      <Grid x:Name="ContentGrid"            Grid.Row="1">            <TextBlock Text="{Binding Welcome}"                     Style="{StaticResource PhoneTextNormalStyle}"                     HorizontalAlignment="Center"                     VerticalAlignment="Center"                     FontSize="40" />        </Grid>      <Preview:Bind

      
    

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