WPF，无法访问控件模板中的控件

Question

我有以下控件模板：

<UserControl x:Class="WpfSinergoHMIControls.Controlli.ControlButton"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
xmlns:local="clr-namespace:WpfSinergoHMIControls.Controlli"
mc:Ignorable="d">
<UserControl.Template>
<ControlTemplate TargetType="UserControl" x:Name="ControlButtonTemplate">
<Grid Background="Black" Name="ControlButtonGrid">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="2*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="1*" />
<RowDefinition Height="2*" />
</Grid.RowDefinitions>
<Label Content="{TemplateBinding Content}" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Background="White" Margin="1,1,1,1" Grid.Row="0"></Label>
<Viewbox Grid.Row="1" Margin="0" HorizontalAlignment="Center" VerticalAlignment="Center">
<Ellipse Width="100" Height="100"  Fill="White" Margin="0" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Viewbox>
<Viewbox Grid.Row="1" Margin="5" HorizontalAlignment="Center" VerticalAlignment="Center">
<Ellipse Width="100" Height="100" Margin="0" Name="InnerEllipse" Fill="Black" HorizontalAlignment="Center" VerticalAlignment="Center"/>
</Viewbox>
</Grid>
</ControlTemplate>
</UserControl.Template>

我想以编程方式访问名为"内椭圆"的对象。

我尝试使用以下代码行执行此操作：

Ellipse InnerEllipse = (Ellipse) this.Template.FindName("InnerEllipse", this);

在"ControlButton"类中名为"Color"的属性中调用：

public Color Color
{
set
{
Ellipse InnerEllipse = (Ellipse)this.Template.FindName("InnerEllipse", this);
}
}

然后，当我使用"用户控件"时初始化属性"颜色">

<Controlli:ControlButton Height="169" Width="119" Color="DarkGreen"/>

问题是函数"FindName"向我返回"null"。我无法弄清楚缺少什么。谢谢！

Answer 1

问题是在应用模板之前设置了Color属性。

Color应该是依赖项属性。然后，您可以指定一个默认值，并挂接一个在更改时调用的PropertyChangedCallback：

public partial class ControlButton : UserControl
{
public ControlButton()
{
InitializeComponent();
}
Ellipse InnerEllipse;
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
InnerEllipse = (Ellipse)this.Template.FindName("InnerEllipse", this);
}
public static readonly DependencyProperty ColorProperty =
DependencyProperty.Register("Color", typeof(Color),
typeof(ControlButton), new FrameworkPropertyMetadata(Colors.DarkGreen, new PropertyChangedCallback(OnColorChanged)));
public Color Color
{
get { return (Color)GetValue(ColorProperty); }
set { SetValue(ColorProperty, value); }
}
private static void OnColorChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
ControlButton ctrl = d as ControlButton;
if (ctrl.InnerEllipse != null)
ctrl.InnerEllipse.Fill = new SolidColorBrush() { Color = ctrl.Color };
}
}