Question

我有一个类型集合的依赖属性，当它的回调基于我需要设置屏幕上某些控件的可见性的计数触发时。

但控制仍然一直在崩溃。根据代码，一个控件始终可见。

XAML绑定

   <TextBlock Text="106 search results for 'a'" Margin="5,0,100,0" Visibility="{Binding CountLabelVisibleReverse, Converter={StaticResource VisibilityConverter}}"/>
 <StackPanel Grid.Row="1" Orientation="Horizontal" Margin="0,0,90,0"  
                            Visibility="{Binding CountLabelVisible, Converter={StaticResource VisibilityConverter}}">
 <TextBlock Text="Sort By"  />
 <ComboBox Style="{StaticResource ComboBoxStyle1}" Width="100" x:Name="ComboBoxSorting" ItemsSource="{Binding SortBy}" />
   </StackPanel>

我的两个属性是

    public bool CountLabelVisible { get; set; }

    public bool CountLabelVisibleReverse { get; set; }

依赖属性回调

   private static void ItemsCollectionChanged(DependencyObject obj, DependencyPropertyChangedEventArgs eventArgs)
    {
        var listingUserControl = (obj as ListingUserControl);

        var itemsResult = (eventArgs.NewValue as List<ItemsResult>);
        if (listingUserControl != null && itemsResult != null)
        {
            listingUserControl.CountLabelVisible = itemsResult.Count > 0;
            listingUserControl.CountLabelVisibleReverse =itemsResult.Count <= 0;
        }
    }

转换器代码

 public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (parameter == null)
            return (bool)value == false ? Visibility.Collapsed : Visibility.Visible;

        return (bool)value ? Visibility.Collapsed : Visibility.Visible;
    }

Answer 1

您犯了经典错误，即绑定到对绑定有效的自动属性，但在更改时不通知，这意味着绑定子系统无法检测更改并更新绑定目标。

要解决此问题，请在您的viewmodel上实施INotifyPropertyChanged，然后确保从属性中通知属性更改。

作为示例，我在viewmodels的基类中有以下内容：

public abstract class BaseViewModel : INotifyPropertyChanged
{

    /// <summary>
    /// Helper method to set the value of a property and notify if the value has changed.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="newValue">The value to set the property to.</param>
    /// <param name="currentValue">The current value of the property.</param>
    /// <param name="notify">Flag indicating whether there should be notification if the value has changed.</param>
    /// <param name="notifications">The property names to notify that have been changed.</param>
    protected bool SetProperty<T>(ref T newValue, ref T currentValue, bool notify, params string[] notifications)
    {
        if (EqualityComparer<T>.Default.Equals(newValue, currentValue))
            return false;

        currentValue = newValue;
        if (notify && notifications.Length > 0)
            foreach (string propertyName in notifications)
                OnPropertyChanged(propertyName);

        return true;
    }

    /// <summary>
    /// Raises the <see cref="E:PropertyChanged"/> event.
    /// </summary>
    /// <param name="propertyName">The name of the property that changed.</param>
    protected void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    /// <summary>
    /// Occurs when a property value changes.
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;

}

然后在常规视图模型中：

public class MyViewModel : BaseViewModel
{
    private bool _countLabelVisible;

    public bool CountLabelVisible
    {
        get { return _countLabelVisible; }
        set { SetProperty(ref value, ref _countLabelVisible, true, "CountLabelVisible", "CountLabelVisibleReverse"); }
    }

    public bool CountLabelVisibleReverse { get { return !_countLabelVisible; }} 
}

这样，当CountLabelVisible发生变化时，它还会通知属性CountLabelVisibleReverse，而属性CountLabelVisibleReverse只包含一个getter - 因为它始终是{{{ 1}}。

因此，您可以按照自己的方式修复代码，但实际情况是您不需要保留CountLabelVisible属性，而是可以：

创建一个逆可见性转换器作为单独的转换器
通过在绑定
堆叠多个转换器，其中一个转换器的输出通过管道传输到下一个转换器的输入

Answer 2

您绑定的布尔属性是否在更改时通知视图？是这样的：

private bool countLabelVisible;
public bool CountLabelVisible
{
  get
  {
    return countLabelVisible;
  }
  set
  {
   if (countLabelVisible != value)
   {
      countLabelVisible = value;
      RaisePropertyChanged(() => CountLabelVisible);
   }
}

对于lambda可用的方法RaisePropertyChanged，您的viewodel应该从NotificationObject继承

Answer 3

您需要通知更改：

public event PropertyChangedEventHandler PropertyChanged;
private bool _countLabelVisible = false;

private void RaisePropertyChanged(string propertyName)
{
    if (PropertyChanged != null)
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}


public bool CountLabelVisible 
{ 
    get
    {
        return _countLabelVisible;
    }
    set
    {
        _countLabelVisible = value;
        RaisePropertyChanged("CountLabelVisible");
    }
}

绑定“框架”需要被告知绑定需要刷新，这就是Raise ...的意思。这非常快速和肮脏（并且未经测试），但应该证明你需要做什么。

Answer 4

Bool到可见性转换器类

    public class BoolToVisibilityConverter : IValueConverter
        {
            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
            {
                return (bool)value ? Visibility.Visible : Visibility.Hidden;
            }

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

下面提到的Xaml更改显示了使用可见性转换器类。此处使用组框来显示可见性。更改单选按钮选择组框将显示/隐藏。

 <Page x:Class="WpfApplication.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:vm="clr-namespace:WpfApplication" HorizontalAlignment="Left" VerticalAlignment="Top"
            Title="Customer"  Loaded="Page_Loaded">
        <Page.Resources>
            <vm:BoolToVisibilityConverter x:Key="converter" 
    </Page.Resources>
<RadioButton Grid.Column="0" x:Name="rdbCustomerDetail"  
    Content="Show Customer" 
    IsChecked="{Binding IsCustomerDetailChecked,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
            <GroupBox Header="Customer Details" Visibility="{Binding 

            Path=IsCustomerDetailChecked, 
            UpdateSourceTrigger=PropertyChanged, 
            Converter={StaticResource  converter}}">
    </GroupBox>

在ViewModel中使用invokepropertychange只会获得xaml上的可见性更改。

private Boolean isCustomerDetailChecked = false;
    public Boolean IsCustomerDetailChecked
    {
        get
        {
            return isCustomerDetailChecked;
        }
        set
        {
            isCustomerDetailChecked = value;
            InvokePropertyChanged("IsCustomerDetailChecked");
        }
    }

在WPF C＃中绑定可见性转换器

4 个答案: