listPicker不会在全屏显示页面中的列表框

Question

我有PivotPage，这是我谈到的pivotItem：

<controls:PivotItem Header="Fotky">
                <Grid>
                    <Grid.Resources>
                        <DataTemplate x:Name="PickerItemTemplate">
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Text="{Binding Name}" Margin="12 0 0 0"/>
                            </StackPanel>
                        </DataTemplate>
                        <DataTemplate x:Name="PickerFullModeItemTemplate">
                            <StackPanel Orientation="Horizontal" Margin="12 0 0 10">
                                <TextBlock Text="{Binding Name}" Margin="0 0 0 0" FontSize="43" FontFamily="{StaticResource PhoneFontFamilyLight}"/>
                            </StackPanel>
                        </DataTemplate>
                    </Grid.Resources>
                    <toolkit:ListPicker  
                        x:Name="listPicker" 
                        SelectedIndex="0"
                        ItemTemplate="{StaticResource PickerItemTemplate}"   
                        ExpansionMode="FullScreenOnly"
                        FullModeItemTemplate="{StaticResource PickerFullModeItemTemplate}"  
                        CacheMode="BitmapCache"
                        SelectionChanged="listPicker_SelectionChanged"/>
                    <ListBox ItemsSource="{Binding Images}" x:Name="listImages">
                        <ListBox.ItemsPanel>
                            <ItemsPanelTemplate>
                                <toolkit:WrapPanel ItemHeight="80" ItemWidth="110"  Height="330"/>
                            </ItemsPanelTemplate>
                        </ListBox.ItemsPanel>
                        <ListBox.ItemTemplate>
                            <DataTemplate>
                                <Image  Margin="10,0,0,0" Tap="Image_Tap">
                                    <Image.Source>
                                        <BitmapImage UriSource="{Binding ImgURL}" CreateOptions="BackgroundCreation"/>
                                    </Image.Source>
                                </Image>
                            </DataTemplate>
                        </ListBox.ItemTemplate>
                    </ListBox>
                </Grid>
            </controls:PivotItem>

问题是，如果没有列表框，listpicker点击它后会全屏显示，但是当我添加列表框时，我尝试点击listpicker，没有任何反应。 Listpicker在那里，但无法点击。谁知道哪里有问题？感谢