DataTemplate.LoadContent 方法

定義

命名空間:

Windows.UI.Xaml

在DataTemplate中建立UIElement物件。

public:
 virtual DependencyObject ^ LoadContent() = LoadContent;

DependencyObject LoadContent();

public DependencyObject LoadContent();

function loadContent()

Public Function LoadContent () As DependencyObject

傳回

DependencyObject

DataTemplate的根UIElement。

範例

下列範例示範如何使用 LoadContent 方法來變更 執行時間的 Border 外觀。 此範例會建立 ListBox ，其中包含數位 1 到 10。 當使用者在 ListBox中選取專案時， Border 會顯示選取的數位。 如果使用者選取偶數，數位會是紅色，且周圍有綠色圓圈。 如果使用者選取奇數，則數位為藍色，且周圍有紫色方塊。

<StackPanel  Name="rootStackPanel">

  <StackPanel.Resources>
    <DataTemplate x:Key="oddNumberTemplate">
      <Grid>
        <Rectangle Stroke="Purple" StrokeThickness="4" />
        <TextBlock HorizontalAlignment="Center" 
                   VerticalAlignment="Center" 
                   FontSize="24" Foreground="Blue" 
                   FontWeight="Bold"/>
      </Grid>
    </DataTemplate>


    <DataTemplate x:Key="evenNumberTemplate">
      <Grid>
        <Ellipse Stroke="Green" StrokeThickness="4"/>
        <TextBlock HorizontalAlignment="Center" 
                   VerticalAlignment="Center" 
                   FontSize="24" Foreground="Red" 
                   FontWeight="Bold"  />
      </Grid>
    </DataTemplate>
  </StackPanel.Resources>

  <Border Name="selectedItemDisplay"
          Width="50" Height="50"/>

  <ListBox Name="numberList" SelectionChanged="ListBox_SelectionChanged">
    <ListBoxItem Content="1"/>
    <ListBoxItem Content="2"/>
    <ListBoxItem Content="3"/>
    <ListBoxItem Content="4"/>
    <ListBoxItem Content="5"/>
    <ListBoxItem Content="6"/>
    <ListBoxItem Content="7"/>
    <ListBoxItem Content="8"/>
    <ListBoxItem Content="9"/>
    <ListBoxItem Content="10"/>
  </ListBox>

</StackPanel>

private void ListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    ListBoxItem lbi = ((sender as ListBox).SelectedItem as ListBoxItem);
    SelectDataTemplate(lbi.Content);
}

private void SelectDataTemplate(object value)
{
    string numberStr = value as string;

    if (numberStr != null)
    {
        int num;

        try
        {
            num = Convert.ToInt32(numberStr);
        }
        catch
        {
            return;
        }

        DataTemplate template;

        // Select one of the DataTemplate objects, based on the 
        // value of the selected item in the ComboBox.
        if (num % 2 != 0)
        {
            template = rootStackPanel.Resources["oddNumberTemplate"] as DataTemplate;
        }
        else
        {
            template = rootStackPanel.Resources["evenNumberTemplate"] as DataTemplate;
        }

        selectedItemDisplay.Child = template.LoadContent() as UIElement;
        TextBlock tb = FindVisualChild<TextBlock>(selectedItemDisplay);
        tb.Text = numberStr;
    }
}

private childItem FindVisualChild<childItem>(DependencyObject obj)
    where childItem : DependencyObject
{
    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);

        if (child != null && child is childItem)
        {
            return (childItem)child;
        }
        else
        {
            childItem childOfChild = FindVisualChild<childItem>(child);
            if (childOfChild != null)
                return childOfChild;
        }
    }
    return null;
}

Private Sub ListBox_SelectionChanged(ByVal sender As Object, ByVal e As SelectionChangedEventArgs)
    Dim lbi As ListBoxItem = CType(CType(sender, ListBox).SelectedItem, ListBoxItem)
    SelectDataTemplate(lbi.Content)

End Sub

Private Sub SelectDataTemplate(ByVal value As Object)
    Dim numberStr As String = CType(value, String)

    If Not numberStr Is Nothing Then
        Dim num As Integer

        Try
            num = Convert.ToInt32(numberStr)
        Catch
            Return
        End Try

        Dim template As DataTemplate


        ' Select one of the DataTemplate objects, based on the 
        ' value of the selected item in the ComboBox.
        If num Mod 2 <> 0 Then
            template = CType(rootStackPanel.Resources("oddNumberTemplate"), DataTemplate)
        Else
            template = CType(rootStackPanel.Resources("evenNumberTemplate"), DataTemplate)
        End If

        selectedItemDisplay.Child = CType(template.LoadContent(), UIElement)
        Dim tb As TextBlock = FindVisualChild(Of TextBlock)(selectedItemDisplay)
        tb.Text = numberStr

    End If
End Sub

Private Function FindVisualChild(Of childItem As DependencyObject) _
        (ByVal obj As DependencyObject) As childItem

    Dim i As Integer

    For i = 0 To VisualTreeHelper.GetChildrenCount(obj) - 1

        Dim child As DependencyObject = VisualTreeHelper.GetChild(obj, i)
        If ((Not child Is Nothing) And (TypeOf child Is childItem)) Then
            Return child
        End If

        Dim childOfChild As childItem = Me.FindVisualChild(Of childItem)(child)
        If (Not childOfChild Is Nothing) Then
            Return childOfChild
        End If

    Next i

    Return Nothing

End Function

備註

當您呼叫 LoadContent 時，會建立 DataTemplate中的UIElement物件，並將它們新增至另一個UIElement的視覺化樹狀結構。