Behaviors擴展----根據Pivot的item自動切換AppBar

 Pivot是Windows Phone中的常用控件，我們經常需要根據PivotItem的切換使用不同的AppBar,在此我提供一個Behaviors

來自動管理AppBar,省去手動切換的麻煩。

  看代碼：

    
   [ContentProperty("AppBars")]
    public class PivotAppBarBehavior : Behavior<Pivot>
    {
        PhoneApplicationPage _page;
        public PhoneApplicationPage ParentPage
        {
            get
            {
                if (_page == null && this.AssociatedObject!=null)
                    _page = this.AssociatedObject.GetParentPhonePage() as PhoneApplicationPage;
                return _page;
            }

        }

        public static readonly DependencyProperty AppBarsProperty = DependencyProperty.Register("AppBars", typeof(List<IApplicationBar>), typeof(PivotAppBarBehavior), null);

        public List<IApplicationBar> AppBars
        {
            get
            {
                var appBars = base.GetValue(AppBarsProperty) as List<IApplicationBar>;
                if (appBars == null)
                {
                    appBars = new List<IApplicationBar>();
                    base.SetValue(PivotAppBarBehavior.AppBarsProperty, appBars);
                }
                return appBars;
            }
            set
            {
                base.SetValue(AppBarsProperty, value);
            }
        }

        void pivot_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (ParentPage == null)
                return;

            if (AssociatedObject != null && AppBars != null && AppBars.Count > AssociatedObject.SelectedIndex)
            {
                IApplicationBar appbar = AppBars[AssociatedObject.SelectedIndex];
                if (appbar is AppBar)
                {
                    AppBar bar = appbar as AppBar;
                    if (bar != null)
                        ParentPage.ApplicationBar = bar.ApplicationBar;
                }
                else
                {
                    ParentPage.ApplicationBar = AppBars[AssociatedObject.SelectedIndex];
                }
            }
            else
            {
                ParentPage.ApplicationBar = null;
            }
        }

        protected override void OnAttached()
        {
            base.OnAttached();
            Pivot pivot = this.AssociatedObject as Pivot;
            if (pivot != null)
                pivot.SelectionChanged += pivot_SelectionChanged;       
        }

        protected override void OnDetaching()
        {
            base.OnDetaching();
            Pivot pivot = this.AssociatedObject as Pivot;
            if (pivot != null)
                pivot.SelectionChanged -= pivot_SelectionChanged;
        }

  這個Behavior中保存一個AppBar的列表，並且會監聽Pivot的Item切換事件，根據Item顯示對應的AppBar，另外還支持

我自定義的一個AppBar，這個AppBar可以使用命令綁定，使用時會很方便,關於這個AppBar點擊這裏：http://www.devdiv.com/home.php?mod=space&uid=55433&do=blog&quickforward=1&id=50584。

  如何使用：

  
        <controls:Pivot>
            <i:Interaction.Behaviors>
                <local:PivotAppBarBehavior>
                    <local:AppBar  Width="0" Height="0" >
                        <local:AppBarIconButton Text="添加" IconUri="/appbar.new.rest.png" Command="{Binding AddItemCommand,Source={StaticResource viewmodel}}" CommandParameter="Add"/>
                        <local:AppBarIconButton Text="減少" IconUri="/appbar.cancel.rest.png" Command="{Binding DecreaseItemCommand,Source={StaticResource viewmodel}}"/>
                    </local:AppBar>
                    <local:AppBar  Width="0" Height="0" >
                        <local:AppBarIconButton Text="添加" IconUri="/appbar.new.rest.png" Command="{Binding AddItemCommand,Source={StaticResource viewmodel}}" CommandParameter="Add"/>
                        <local:AppBar.Menus>
                            <local:AppBarMenuItem Text="減少"  Command="{Binding DecreaseItemCommand,Source={StaticResource viewmodel}}"/>
                        </local:AppBar.Menus>
                    </local:AppBar>
                    <local:AppBar  Width="0" Height="0" >
                        <local:AppBarIconButton Text="減少" IconUri="/appbar.cancel.rest.png" Command="{Binding DecreaseItemCommand,Source={StaticResource viewmodel}}"/>
                        <local:AppBar.Menus>
                            <local:AppBarMenuItem Text="添加"  Command="{Binding AddItemCommand,Source={StaticResource viewmodel}}"  CommandParameter="PivotItem3Add"/>
                        </local:AppBar.Menus>
                    </local:AppBar>
                </local:PivotAppBarBehavior>
            </i:Interaction.Behaviors>

  使用與正常的Behavior是一樣的，注意第一個AppBar對應第一個PivotItem,第二個AppBar對應第二個PivotItem，以此類推。

   看效果：

  

  示例：AppBarCommand.zip