Windows 8 系列（十一）：開發小技巧分享

臨時記錄、分享一些小的開發技巧：

1. 在資料繫結時，如果資料來源需要被清空：collection.Clear()； 建議在語句後把集合置為null：collection.Clear(); collection=  null;（開發過程中因為沒有置為null而報錯，Windows.UI.Xaml.dll的錯誤）

2. async void 函數與async Task函數不能混為一談。

　async void FUNCTIONNAME1(){ ...  await ...;  Debug.WriteLine("FUNCTIONNAME1 over")};   

   async Task FUNCTIONNAME2(){ ...  await ...;  Debug.WriteLine("FUNCTIONNAME2 over")};

   section1: FUNCTIONNAME1(); Debug.WriteLine("FUNCTIONNAME1")；

　section2: await FUNCTIONNAME2(); Debug.WriteLine("FUNCTIONNAME2")；

   以上兩段代碼中section1的代碼在執行時會非同步執行，有可能先輸出FUNCTIONNAME1，然後輸出FUNCTIONNAME1 over。第二段代碼則能保證在輸出FUNCTIONNAME2 over後再輸出FUNCTIONNAME2。

3. 你的代碼是不是真的實現了虛擬化？不能單單看你的代碼是不是寫了相關控制項，而需要用VirtualizingStackPanel的CleanUpVirtualizedItemEvent事件來確定是不是真正的實現了虛擬化。我們在gridview的style中修改了樣式，導致上述事件不觸發：

<Style x:Key="PaddingGridViewStyle" TargetType="GridView">        <Setter Property="Padding" Value="0,0,0,10"/>        <Setter Property="IsTabStop" Value="False"/>        <Setter Property="TabNavigation" Value="Once"/>        <Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>        <Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Disabled"/>        <Setter Property="ScrollViewer.HorizontalScrollMode" Value="Enabled"/>        <Setter Property="ScrollViewer.IsHorizontalRailEnabled" Value="False"/>        <Setter Property="ScrollViewer.VerticalScrollMode" Value="Disabled"/>        <Setter Property="ScrollViewer.IsVerticalRailEnabled" Value="False"/>        <Setter Property="ScrollViewer.ZoomMode" Value="Disabled"/>        <Setter Property="IsSwipeEnabled" Value="True"/>        <Setter Property="ItemContainerTransitions">            <Setter.Value>                <TransitionCollection>                    <AddDeleteThemeTransition/>                    <ContentThemeTransition/>                    <ReorderThemeTransition/>                    <EntranceThemeTransition IsStaggeringEnabled="False"/>                </TransitionCollection>            </Setter.Value>        </Setter>        <Setter Property="Template">            <Setter.Value>                <ControlTemplate TargetType="GridView">                    <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="1">                        <ScrollViewer x:Name="ScrollViewer" HorizontalScrollMode="{TemplateBinding ScrollViewer.HorizontalScrollMode}" HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}"                                       IsHorizontalRailEnabled="{TemplateBinding ScrollViewer.IsHorizontalRailEnabled}" IsHorizontalScrollChainingEnabled="{TemplateBinding ScrollViewer.IsHorizontalScrollChainingEnabled}" IsVerticalScrollChainingEnabled="{TemplateBinding ScrollViewer.IsVerticalScrollChainingEnabled}"                                       IsVerticalRailEnabled="{TemplateBinding ScrollViewer.IsVerticalRailEnabled}" TabNavigation="{TemplateBinding TabNavigation}" VerticalScrollBarVisibility="{TemplateBinding ScrollViewer.VerticalScrollBarVisibility}" VerticalScrollMode="{TemplateBinding ScrollViewer.VerticalScrollMode}"                                       ZoomMode="{TemplateBinding ScrollViewer.ZoomMode}">                            <Grid Margin="{TemplateBinding Padding}">                                <ItemsPresenter HeaderTemplate="{TemplateBinding HeaderTemplate}" Header="{TemplateBinding Header}" HeaderTransitions="{TemplateBinding HeaderTransitions}" />                            </Grid>                        </ScrollViewer>                    </Border>                </ControlTemplate>            </Setter.Value>        </Setter>    </Style>

代碼中紅色的部分導致虛擬化被破壞，修改後

<ScrollViewer x:Name="ScrollViewer" ...>     <ItemsPresenter HeaderTemplate="{TemplateBinding HeaderTemplate}" Header="{TemplateBinding Header}" Margin="{TemplateBinding Padding}" HeaderTransitions="{TemplateBinding HeaderTransitions}" /></ScrollViewer>