WPF DataTrigger doesn't work.

问题:

I designed a WPF Page and it should be possible to change the theme (dark theme and light theme). I am a newbie in WPF and found a solution to my problem using DataTrigger, but it don't works. 3 hours later I tried like 10 different solutions/tutorials but I don't know what I am doing wrong...

The xml code:

<Page   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:VMQWPFApplication.Pages" x:Class="VMQWPFApplication.Pages.MainPage"    mc:Ignorable="d"    d:DesignHeight="400" d:DesignWidth="600" Title="MainPage">  <Page.Resources>     <Style x:Key="styleWithTrigger" TargetType="{x:Type Rectangle}">         <Setter Property="Fill" Value="Blue"/>         <Style.Triggers>             <DataTrigger Binding="{Binding DarkTheme, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:MainPage}}}" Value="True">                 <Setter Property="Fill" Value="Red"/>             </DataTrigger>         </Style.Triggers>     </Style> </Page.Resources>  <DockPanel>     <!--Toolbar-->     ...      <!--Body-->     <Grid>         <Rectangle Style="{StaticResource styleWithTrigger}"/>     </Grid> </DockPanel> 

And here the cs:

namespace VMQWPFApplication.Pages {     /// <summary>     /// Interaction logic for MainPage.xaml     /// </summary>     public partial class MainPage : Page     {         public bool DarkTheme { get; set; }          public MainPage()         {             InitializeComponent();             DarkTheme = false;         }          private void TestButton_Click(object sender, RoutedEventArgs e)         {             DarkTheme = true;         }     } } 

At the beginning the rectangle is blue, but it won't change.

回答1:

Your MainPage.xaml.cs file does not implement the INotifyPropertyChanged interface. To do so you should add/change the following:

public partial class MainPage : Page, INotifyPropertyChanged  #region INotifyPorpertyChanged Memebers       public event PropertyChangedEventHandler PropertyChanged;      protected void NotifyPropertyChanged(string propertyName = "")     {         if (PropertyChanged != null)             PropertyChanged(this, new PropertyChangedEventArgs(propertyName));     }  #endregion 

I would change your DarkTheme property to:

private bool _darkTheme; public bool DarkTheme { get { return _darkTheme; } set { _darkTheme = value; NotifyPropertyChanged("DarkTheme"); } 

Now when you update DarkTheme it will raise the Change Property Event. I would also put the DataContext into the Page make up:

DataContext="{Binding RelativeSource={RelativeSource Self}}" 

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