访问自定义控件 wpf c# 的子级

Question

我对 WPF 很有经验 UserControl，我想尝试自定义控件。这是我目前所拥有的：

Generic.XAML

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:local="clr-namespace:testapp">
    <Style TargetType="{x:Type local:testcontrol}">
        <Setter Property="Height" Value="45"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:testcontrol}">
                    <TextBlock x:Name="tb" Text="test"/>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

CustomControl.Cs

using System.Windows.Controls.Primitives;

public class testcontrol : System.Windows.Controls.Control
{
    public TextBlock tb;

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        tb = this.GetTemplateChild("tb");
    }

    public static test()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof (testcontrol), new FrameworkPropertyMetadata(typeof (testcontrol)));
    }

    private void testcontrol_MouseDown(object sender, MouseButtonEventArgs e)
    {
        tb.Text = "Abc";
    }
}

现在，当触发 MouseDown 事件时，TextBlock 的文本发生变化，这意味着文本块是 found/accessible...

但是当我从我的 window 中做同样的事情时，如下所示：

 private void test()
 {
     testcontrol tt = new testcontrol();
     tt.tb.Text = "abc";
 }

a NullReferenceException 被抛出。我想知道为什么找不到 TextBlock？任何解释将不胜感激。

最后一件事，我刚开始使用自定义控件，所以请指出我的方法是否正确:)

Answer 1

您可以将此扩展方法放在辅助程序中 class

public static IEnumerable<T> GetVisualChildren<T>(this DependencyObject parent) where T : DependencyObject
{
    if (parent == null)
    {
        yield return null;
    }

    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(parent, i);

        if (child is T t)
        {
            yield return t;
        }

        foreach (T childrensChild in child.FindVisualChildren<T>())
        {
            yield return childrensChild;
        }
    }
}

然后你可以像这样使用它：

testcontrol tt = new testcontrol();
IEnumerable<TextBlock> allTextBlocks = tt.GetVisualChildren<TextBlock>();

在你的 testcontrol 中获取 所有 TextBlock。

特别是对于你的情况，你可以使用

testcontroll tt = new testcontrol(); IEnumerable<TextBlock> allTextBlocks = tt.GetVisualChildren<TextBlock>(); TextBlock tb = allTextBlocks.Single(t => t.Name = "tb"); if(tb != null) { tb.Text = "abc"; }

我不确定 FindTemplateChild<T> 在这里是否有用；至少它已经内置了，所以你可以试试看。

Answer 2

如评论所述，您应该使用依赖关系属性或路由事件来更新 child 模板化 parent 而不是直接访问。

下面是自定义控件的简单示例，它前面有 Header (TextBlock)。

[TemplatePart(Name = "PreText", Type = typeof(TextBlock))]
public class ExtendedTextBox : TextBox
{
    public static readonly DependencyProperty PreTextDependency = DependencyProperty.Register("PreText", typeof(string), typeof(ExtendedTextBox));

    public string PreText
    {
        get
        {
            return (string)GetValue(PreTextDependency);
        }

        set
        {
            SetValue(PreTextDependency, value);
        }
    }

    private TextBlock preTextBlock;

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        preTextBlock = GetTemplateChild("PreText") as TextBlock;
        Binding preTextBinding = new Binding("PreText");
        preTextBinding.Source = this;
        preTextBinding.Mode = BindingMode.TwoWay;
        preTextBlock.SetBinding(TextBlock.TextProperty, preTextBinding);
    }
}

XAML 这个 ExtendedTextBox:

    <SolidColorBrush x:Key="TextBox.Static.Border" Color="#FFABAdB3"/>
    <SolidColorBrush x:Key="TextBox.MouseOver.Border" Color="#FF7EB4EA"/>
    <SolidColorBrush x:Key="TextBox.Focus.Border" Color="#FF569DE5"/>
    <Style x:Key="ExtendedTextBoxStyle" TargetType="{x:Type local:ExtendedTextBox}">
        <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"/>
        <Setter Property="BorderBrush" Value="{StaticResource TextBox.Static.Border}"/>
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="KeyboardNavigation.TabNavigation" Value="None"/>
        <Setter Property="HorizontalContentAlignment" Value="Left"/>
        <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
        <Setter Property="AllowDrop" Value="true"/>
        <Setter Property="ScrollViewer.PanningMode" Value="VerticalFirst"/>
        <Setter Property="Stylus.IsFlicksEnabled" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:ExtendedTextBox}">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>
                        <TextBlock Grid.Column="0" Text="{Binding PreText}" Name="PreText" IsHitTestVisible="False" />
                        <Border Grid.Column="1" x:Name="border" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
                            <ScrollViewer x:Name="PART_ContentHost" Focusable="false" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden"/>
                        </Border>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsEnabled" Value="false">
                            <Setter Property="Opacity" TargetName="border" Value="0.56"/>
                        </Trigger>
                        <Trigger Property="IsMouseOver" Value="true">
                            <Setter Property="BorderBrush" TargetName="border" Value="{StaticResource TextBox.MouseOver.Border}"/>
                        </Trigger>
                        <Trigger Property="IsKeyboardFocused" Value="true">
                            <Setter Property="BorderBrush" TargetName="border" Value="{StaticResource TextBox.Focus.Border}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <MultiTrigger>
                <MultiTrigger.Conditions>
                    <Condition Property="IsInactiveSelectionHighlightEnabled" Value="true"/>
                    <Condition Property="IsSelectionActive" Value="false"/>
                </MultiTrigger.Conditions>
                <Setter Property="SelectionBrush" Value="{DynamicResource {x:Static SystemColors.InactiveSelectionHighlightBrushKey}}"/>
            </MultiTrigger>
        </Style.Triggers>
    </Style>

如何在XAML中定义：

    <local:ExtendedTextBox x:Name="extendedTextBox" Grid.Row="1" Style="{StaticResource ExtendedTextBoxStyle}" Text="Some Text!!" PreText="Pre Text :" />

现在你应该如何更新模板 child 值（我给的名字是 extendedTextBox）：

this.extendedTextBox.PreText = "I'm clicked";

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