触发器与依赖关系属性优先级

Question

我对依赖项属性值的优先级有疑问。我的 .xaml 如下所示：

<Window x:Class="WpfTests.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local ="clr-namespace:WpfTests"
    Title="MainWindow" Height="350" Width="525">
<Window.Style>
    <Style>
        <!--<Setter Property="Canvas.Background" Value="Gray"/>-->
        <Style.Triggers>
            <Trigger Property="local:MainWindow.IsMouseOver" Value="True">
                <!--<Setter Property="local:LeistenPfeil.Symbolfarbe" Value="Red"/>-->
                <Setter Property="local:MainWindow.Cursor" Value="Hand" />
                <Setter Property="local:MainWindow.BG" Value="Blue"/>
            </Trigger>
        </Style.Triggers>
    </Style>
</Window.Style>

<Grid Background="{Binding BG,Mode=TwoWay}">
    <Button Content="ChangeBG" HorizontalAlignment="Center" VerticalAlignment="Center" Click="OnClick"/>
</Grid>

在我的代码隐藏中，我创建了依赖项属性 'BG'，例如：

public partial class MainWindow : Window
{
    public Brush BG
    {
        get { return (Brush)GetValue(BGProperty); }
        set { SetValue(BGProperty, value); }
    }

    // Using a DependencyProperty as the backing store for BG.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty BGProperty =
        DependencyProperty.Register("BG", typeof(Brush), typeof(MainWindow), new PropertyMetadata(Brushes.Black));


    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
    }

    private void OnClick(object sender, RoutedEventArgs e)
    {
        BG = Brushes.Green;
    }
}

因此，启动时背景设置为黑色（DP 的默认设置）。当鼠标悬停时，背景变为蓝色。当涉及到我的代码隐藏中 BG-属性的更改时，触发器确实起作用，但它对网格背景的影响消失了。我已经在 MSDN 上阅读了这篇文章： https://msdn.microsoft.com/en-us/library/ms743230%28v=vs.110%29.aspx

我理解的问题是：为什么触发器在 BG-属性具有其默认值时起作用，而当它在后面的代码中更改时却不起作用？ => 背景的最高优先级是网格的本地背景绑定，那么为什么触发器会起作用？

在代码隐藏中更改 BG-属性后，如何让触发器再次工作？

Answer 1

您的代码更改实际上被视为本地更改。从您在 MSDN 上的链接页面：

Local value. A local value might be set through the convenience of the "wrapper" property, which also equates to setting as an attribute or property element in XAML, or by a call to the SetValue API using a property of a specific instance. If you set a local value by using a binding or a resource, these each act in the precedence as if a direct value was set.

我突出显示了相关部分，指出像您那样调用 SetValue（通过您的 BG CLR 属性）将导致 Local 改变。由于 Local 更改的优先级高于 Trigger，它否决了 Trigger 值。

Answer 2

而不是

BG = Brushes.Green;

设置一个局部值比触发器更高的优先级，你可以这样写

SetCurrentValue(BGProperty, Brushes.Green);

来自MSDN：

... The SetCurrentValue method changes the effective value of the property, but existing triggers, data bindings, and styles will continue to work.

触发器与依赖关系属性优先级

Trigger vs. Dependency Property precendence

.net

c#

wpf

triggers

dependency-properties

触发器与依赖关系 属性 优先级

Trigger vs. Dependency Property precendence

.net

c#

wpf

triggers

dependency-properties

触发器与依赖关系属性优先级