VisualTreeHelper.GetChildrenCount returns 0

Hi, I have a xamDataChart, below is  the xaml code:

<ig:XamDataChart x:Name=”xmDataChart” SeriesMouseLeftButtonDown=”xmDataChart_SeriesMouseLeftButtonDown” Margin=”0,0,0,0″ Legend=”{Binding ElementName=xmLegend}”>
<ig:XamDataChart.Axes>
<ig:CategoryXAxis x:Name=”xmDateXAxis” Gap=”1″ Opacity=”0.3″ Interval=”1″ ItemsSource=”{Binding}” Label=”{}{MTime:yyyy-MM}”>
<ig:CategoryXAxis.LabelSettings>
<ig:AxisLabelSettings Location=”OutsideTop” Extent=”20″ />
</ig:CategoryXAxis.LabelSettings>
</ig:CategoryXAxis>
<ig:NumericYAxis x:Name=”xmWaterLevelYAxis” Opacity=”0.3″ IsInverted=”True” Label=” { }米”>
<ig:NumericYAxis.LabelSettings>
<ig:AxisLabelSettings Location=”OutsideLeft” Extent=”50″/>
</ig:NumericYAxis.LabelSettings>
</ig:NumericYAxis>
</ig:XamDataChart.Axes>
<ig:XamDataChart.Series>
<ig:LineSeries MarkerType=”Circle” Brush=”DarkRed” MarkerBrush=”DarkRed” x:Name=”lsManaNa” ValueMemberPath=”WaterLevel” ItemsSource=”{Binding}”
XAxis=”{Binding ElementName=xmDateXAxis}”
YAxis=”{Binding ElementName=xmWaterLevelYAxis}”>
<ig:LineSeries.ToolTip>
<StackPanel Orientation=”Horizontal”>
<TextBlock Text=”月份=”></TextBlock>
<TextBlock Text=”{Binding Item.MTime, StringFormat=yyyy年MM月}” Foreground=”{Binding ForegroundBrush}” />
<TextBlock Text=” , 水位= ” />
<TextBlock Text=”{Binding Item.WaterLevel,StringFormat=0.00}” Foreground=”{Binding ForegroundBrush}” />
<TextBlock Text=”米”/>
</StackPanel>
</ig:LineSeries.ToolTip>
<ig:LineSeries.LegendItemTemplate>
<DataTemplate>
<Border
BorderBrush=”Black”
BorderThickness=”1″
Margin=”2″
CornerRadius=”5″
Visibility=”{Binding Series.Visibility}”>
<StackPanel Orientation=”Horizontal”
Margin=”5″
Width=”150″>
<CheckBox x:Name=”WaterChangValue”
Click=”WaterChangValue_Click”
IsChecked=”True”
VerticalAlignment=”Center”
HorizontalAlignment=”Left” >
</CheckBox>
<ContentPresenter Content=”{Binding}”
ContentTemplate=”{Binding Series.LegendItemBadgeTemplate}” />
<ContentPresenter Content=”水位(米)”
Margin=”3″ />
</StackPanel>
</Border>
</DataTemplate>
</ig:LineSeries.LegendItemTemplate>
<ig:LineSeries.LegendItemBadgeTemplate>
<DataTemplate>
<Grid Width=”18″
Height=”16″
Margin=”0 0 2 0″>
<Grid.Effect>
<DropShadowEffect Color=”Black”
BlurRadius=”5″
ShadowDepth=”4″
Opacity=”0.5″></DropShadowEffect>
</Grid.Effect>
<Line VerticalAlignment=”Center”
HorizontalAlignment=”Center”
X1=”0″
Y1=”0″
X2=”16″
Y2=”0″
Stroke=”{Binding Series.ActualBrush}”
StrokeThickness=”{Binding Series.Thickness}”
StrokeEndLineCap=”{Binding Series.EndCap}”
StrokeStartLineCap=”{Binding Series.StartCap}”
Effect=”{Binding Series.Effect}” />
<ContentPresenter Width=”11″
Height=”11″
VerticalAlignment=”Center”
HorizontalAlignment=”Center”
Margin=”0 0 2 0″
ContentTemplate=”{Binding Series.ActualMarkerTemplate}”
Content=”{Binding}” />
</Grid>
</DataTemplate>
</ig:LineSeries.LegendItemBadgeTemplate>
</ig:LineSeries>
</ig:XamDataChart.Series>
</ig:XamDataChart>

I just want to access the ContentPresenter  control in LineSeries.LegendItemTemplate, change the control’s content, so I used the visualTreeHelper method, and below is my C# code:

a private method:

private void GetChildren(UIElement parent, Type targetType, ref List<UIElement> children)
{
int count = VisualTreeHelper.GetChildrenCount(parent);
if (count > 0)
{
for (int i = 0; i < count; i++)
{
UIElement child = (UIElement)VisualTreeHelper.GetChild(parent, i);
if (child.GetType() == targetType)
{
children.Add(child);
}
GetChildren(child, targetType, ref children);
}
}
}

Constructor method:

public UcGroundWater()
{
InitializeComponent();
List<UIElement> items = new List<UIElement>();
GetChildren(xmDataChart, typeof(ContentPresenter), ref items);
((ContentPresenter)items[1]).Content = “Water Level(m)”;
}

When I debug, I find VisualTreeHelper.GetChildrenCount(parent) always return 0,  so I can’t access the ContentPresenter  control.

Do I make myself clear?  Thanks in advance~~

Anyone can help me ?   Thanks~~

Hello Charlie,

 

Thank you for your post. I have been looking into it and I can say that the behavior you have is expected, because the XamDataChart is not rendered by the time you execute the code for finding the child elements. If you put the code in Button’s Click handler you will see that the collection will get populated.

 

Hope this helps you.