DataTrigger 不会更改 Text 属性 [英] DataTrigger does not change Text property

问题描述

我试图在样式上使用数据触发器来更改属性.

I'm attempting to use a data-trigger on a style to change a property.

符合最小、完整和可验证示例"要求...

要重现，首先在 Visual Studio 中创建一个 WPF 应用程序.

To reproduce, first create a WPF application in Visual Studio.

在 App.xaml.cs 中:

Within the App.xaml.cs :

using System.ComponentModel;
using System.Windows;

namespace Foo{
/// <summary>
/// Interaction logic for App.xaml
/// </summary>
public partial class App : Application, INotifyPropertyChanged {
        private bool _clicked;
        public bool Clicked {
            get { return this._clicked; }
            set {
                this._clicked = value;
                this.PropertyChanged?.Invoke(
                    this, new PropertyChangedEventArgs( "Clicked" ) );
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

在 MainWindow.xaml 中:

Within the MainWindow.xaml :

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:lib="clr-namespace:System;assembly=mscorlib"
    xmlns:local="clr-namespace:Foo"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    mc:Ignorable="d" x:Class="Foo.MainWindow"
    Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <lib:Boolean x:Key="True">True</lib:Boolean>
    </Window.Resources>
    <Grid>
        <Button x:Name="button" Click="button_Click">
            <Viewbox>
                <TextBlock Text="Unclicked">
                    <TextBlock.Style>
                        <Style TargetType="{x:Type TextBlock}">
                            <Style.Triggers>
                                <DataTrigger
                                        Binding="{Binding
                                            Clicked,
                                            Source={x:Static Application.Current}}"
                                            Value="{StaticResource True}">
                                    <Setter Property="Text" Value="Clicked" />
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </TextBlock.Style>
                </TextBlock>
            </Viewbox>
        </Button>
    </Grid>
</Window>

在 MainWindow.xaml.cs 内 -

Within the MainWindow.xaml.cs -

using System.Windows;

namespace Foo{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window {
        public MainWindow( ) {
            InitializeComponent( );
        }

        private void button_Click( object sender, RoutedEventArgs e ) {
            ( Application.Current as App ).Clicked = !( Application.Current as App ).Clicked;
        }
    }
}

作为旁注 - 我尝试将数据触发器的值设置为 "True"，但这也不起作用(触发器没有捕获，文本也没有根据将属性设置为新值).

As a side note - I tried setting the value of the data trigger to just "True", and that also did not work ( the trigger did not catch, and text did not change based on setting the property to a new value ).

那么为什么数据触发器在这里没有捕获或工作?(无论是静态资源还是文字值)?更重要的是 - 为什么我会收到这个错误?在使用‘DataTrigger’(密封)后，无法修改"错误?完成我在这里尝试做的事情的正确方法是什么?(最好仍然使用数据触发器而不是转换器，因为我确实需要在两个值之间切换).

So why is the data-trigger not catching or working here? ( Either with the static resource or the literal value )? Even more relevant - why am I getting this error? The "After a 'DataTrigger' is in use (sealed), it cannot be modified" error? And what is the proper method of accomplishing what I am trying to do here? ( Preferably still using a data-trigger and not a converter, since I do need to switch between two values ).

推荐答案

分配给 TextBlock 的 Text 属性的本地值的优先级高于 DataTrigger 中 Setter 提供的值.有关详细信息，请参阅依赖属性值优先级.

The local value assigned to the TextBlock's Text property has higher precedence than the value provided by the Setter in the DataTrigger. See Dependency Property Value Precedence for details.

由另一个 Setter 设置初始 Text 值:

Set the initial Text value by another Setter:

<TextBlock>
    <TextBlock.Style>
        <Style TargetType="TextBlock">
            <Setter Property="Text" Value="Unclicked"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding Clicked,
                                       Source={x:Static Application.Current}}"
                             Value="{StaticResource True}">
                    <Setter Property="Text" Value="Clicked" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </TextBlock.Style>
</TextBlock>

您在使用布尔资源时看到的错误消息只是 XAML 设计者的抱怨.运行时没有错误.

The error message you see when you use the Boolean resource is just the XAML designer complaining. There is no error at runtime.

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