MultiDataTrigger具有OR而不是和

Question

我正试图在我的Button上设置多个Button。我做了一些研究，发现MultiDataTrigger允许您这样做。如果Visibility或PermissionsFlag == false设置为false，则希望将Button的CCTVPath == string.Empty属性设置为false。到目前为止，这就是我所拥有的；

<Button Grid.Column="3" x:Name="cctvFeedButton" Content="Live Feed"
        Width="100" FontSize="16" HorizontalAlignment="Right" Margin="5" Click="OnCCTVButtonClick">
    <Button.Style>
        <Style TargetType="Button">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition Binding="{Binding CCTVPath}" Value=""/>
                        <Condition Binding="{Binding PermissionsFlag}" Value="False"/>
                    </MultiDataTrigger.Conditions>
                    <Setter Property="Visibility" Value="Hidden"/>
                </MultiDataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

在我的代码背后，我像这样设置了PermissionsFlag；

public bool PermissionsFlag { get; set; }

private void OnPageLoaded(object sender, RoutedEventArgs e)
{
    PermissionsFlag = false;
}

如您所见，PermissionsFlag绝对是假的，而且肯定有空的CCTVPath，但是Button永远不会隐藏。我做错了什么？

更新：

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    private bool _permissionsFlag;
    public bool Flag
    {
        get { return _permissionsFlag; }
        set
        {
            _permissionsFlag = value;
            OnPropertyChanged("PermissionsFlag");
        }
    }

    private void OnPageLoaded(object sender, RoutedEventArgs e)
    {
        Flag = false;
        CCTVImageCollection = GetImages();
        imageListBox.ItemsSource = CCTVImageCollection;
        DataContext = this;
    }

在我的XAML中：

<Button.Style>
         <Style TargetType="Button">
               <Style.Triggers>
                      <DataTrigger Binding="{Binding PermissionsFlag}" Value="False">
                            <Setter Property="Visibility" Value="Hidden"/>
                      </DataTrigger>
               </Style.Triggers>
         </Style>
 </Button.Style>

Answer 1

将条件转化为两个独立的DataTriggers

<Style.Triggers>
    <DataTrigger Binding="{Binding CCTVPath}" Value="">
        <Setter Property="Visibility" Value="Hidden"/>
    </DataTrigger>
    <DataTrigger Binding="{Binding PermissionsFlag}" Value="False">
        <Setter Property="Visibility" Value="Hidden"/>
    </DataTrigger>
</Style.Triggers>

确保绑定路径是正确的(检查VS输出窗口中可能出现的异常消息)

​

另外:不要只依赖于按钮的隐藏状态，在代码(OnCCTVButtonClick)中正确地实现权限。请阅读这里的原因：

​

How to Snoop proof your wpf application?

​

​

auto (public bool PermissionsFlag { get; set; })不通知视图更改。

可以实现INotifyPropertyChanged接口(在我的测试窗口中这样做：public partial class Window3 : Window, INotifyPropertyChanged)，然后在属性更改时引发事件。

下面是我用来测试的一个完整的工作示例

public partial class Window3 : Window, INotifyPropertyChanged
{
    public Window3()
    {
        InitializeComponent();
        this.DataContext = this;
        //PermissionsFlag = true;
        CCTVPath = "youtube.com";
    }

    private bool _permissionsFlag = false;
    private string _cctvPath;

    public bool PermissionsFlag
    {
        get { return _permissionsFlag; }
        set
        {
            _permissionsFlag = value;
            OnPropertyChanged("PermissionsFlag");
        }
    }

    public string CCTVPath
    {
        get { return _cctvPath; }
        set
        {
            _cctvPath = value;
            OnPropertyChanged("CCTVPath");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

窗口xaml：

<Window x:Class="WpfDemos.Views.Window3"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window3" Height="300" Width="300">
    <StackPanel>
        <CheckBox Name="chkPermissionsFlag" 
                  Content="PermissionsFlag" 
                  IsChecked="{Binding Path=PermissionsFlag, UpdateSourceTrigger=PropertyChanged}"/>

        <TextBox Text="{Binding Path=CCTVPath, UpdateSourceTrigger=PropertyChanged}"/>

        <Button x:Name="cctvFeedButton" Content="Live Feed"
                    Width="100" FontSize="16" HorizontalAlignment="Right" Margin="5">
            <Button.Style>
                <Style TargetType="Button">
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding Path=CCTVPath}" Value="">
                            <Setter Property="Visibility" Value="Hidden"/>
                        </DataTrigger>
                        <DataTrigger Binding="{Binding Path=PermissionsFlag}" Value="False">
                            <Setter Property="Visibility" Value="Hidden"/>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </Button.Style>
        </Button>
    </StackPanel>
</Window>

Answer 2

另一种解决方案是使用单个DataTrigger和一个MultiBinding。您可以通过定义一个“特例”IMultiValueConverter来使其工作，它假定对象数组中有两个项，如果第一个项为空字符串或第二个项为false，则返回true。但是，您可能永远不会在代码中的任何其他地方使用该转换器。因此，如果您愿意在前面做更多的工作，您可以定义3个简单/可重用的转换器。

1) IMultiValueConverter 'OrConverter‘，它看起来如下所示：

public class BooleanOrConverter : IMultiValueConverter {
   public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) {
      return values.OfType<bool>().Any(b => b);
   }

   public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) {
      throw new NotImplementedException();
   }
}

2) IValueConverter 'IsNullOrEmpty‘字符串转换器：

public class StringIsNullOrEmptyConverter : IValueConverter {
   public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
      return string.IsNullOrEmpty(value as string);
   }

   public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
      throw new NotImplementedException();
   }
}

3)和IValueConverter 'NotConverter:‘

public class BooleanNotConverter : IValueConverter {
   public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
      return !(bool)value;
   }

   public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
      throw new NotImplementedException();
   }
}

然后，在xaml中，DataTrigger的定义如下：

<Button x:Name="cctvFeedButton" Content="Live Feed"
  Width="100" FontSize="16" HorizontalAlignment="Right" Margin="5">
  <Button.Style>
    <Style TargetType="Button">
      <Style.Triggers>
         <DataTrigger Value="True">
           <DataTrigger.Binding>
             <MultiBinding Converter="{StaticResource OrConverter}">
               <Binding Path="PermissionFlag" Converter="{StaticResource NotConverter}"/>
               <Binding Path="CCTVPath" Converter="{StaticResource IsNullOrEmptyConverter}"/>
             </MultiBinding>
           </DataTrigger.Binding>
           <Setter Property="Visibility" Value="Hidden"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </Button.Style>
</Button>

我更喜欢这个解决方案，而不是使用两个单独的DataTriggers来提高可读性；它更好地表达了您正在定义的行为--它是‘或’逻辑:一个由两个条件组成的奇异集合，应该隐藏按钮。

Answer 3

当文本框为空时，我使用这些触发器禁用Add按钮：

或者(如果之一的文本框被填充，按钮将启用)

<MultiDataTrigger>
    <MultiDataTrigger.Conditions>
        <Condition Binding="{Binding Text, ElementName=Usernametxtbox}" Value=""/>
        <Condition Binding="{Binding Password, ElementName=passtxtbox}" Value=""/>
    </MultiDataTrigger.Conditions>
    <Setter Property="IsEnabled" Value="False" />
</MultiDataTrigger>

而且(如果两个文本框都被填充，则按钮将启用)

<DataTrigger Binding="{Binding Text, ElementName=Usernametxtbox}" Value="">
    <Setter Property="IsEnabled" Value="False" />
</DataTrigger>

<DataTrigger Binding="{Binding Password, ElementName=passtxtbox}" Value="">
    <Setter Property="IsEnabled" Value="False" />
</DataTrigger>