c# - 绑定(bind)到 Children.Count

我正在使用表单的绑定(bind)

{Binding RelativeSource={RelativeSource Self}, Path=Children.Count, Converter={StaticResource CountToDimensionConverter}, ConverterParameter=Rows}

尽管在 xaml 中添加了 child ，但当我中断转换器时，该值始终为 0。

我假设正在发生的是在调用此绑定(bind)之前不会添加子项。

我还假设绑定(bind)在被调用一次后被破坏，因为 .Count 是一个只读属性(我之前遇到过类似的问题，我不得不在属性中添加一个空的 setter 来维护绑定(bind)并愚弄 WPF)因此添加子项后绑定(bind)不会更新。

但是，我被困在您为问题提出解决方案并使其发挥作用的地方... =/

<UniformGrid x:Name="MyUniformGrid"
     Rows="{Binding RelativeSource={RelativeSource Self}, Path=Children.Count, Converter={StaticResource CountToDimensionConverter}, ConverterParameter=R}"
     Columns="{Binding RelativeSource={RelativeSource Self}, Path=Children.Count, Converter={StaticResource CountToDimensionConverter}, ConverterParameter=C}">
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
   </UniformGrid>

谢谢，
兔子

最佳答案

这是因为 UIElementCollection(Children 属性的类型)在添加或删除新项目时不会引发通知，因此不会刷新绑定(bind)

但是，您可以创建自己的自定义 UniformGrid ，并覆盖 CreateUIElementCollection 属性以创建继承 UIElementCollection 并实现 INotifyCollectionChanged 的自定义集合的实例。

这是一个基本的实现:

ObservableUIElementCollection

public class ObservableUIElementCollection : UIElementCollection, INotifyCollectionChanged, INotifyPropertyChanged
{
    public ObservableUIElementCollection(UIElement visualParent, FrameworkElement logicalParent)
        : base(visualParent, logicalParent)
    {
    }

    public override int Add(UIElement element)
    {
        int index = base.Add(element);
        var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, element, index);
        OnCollectionChanged(args);
        OnPropertyChanged("Count");
        OnPropertyChanged("Item[]");
        return index;
    }

    public override void Clear()
    {
        base.Clear();
        OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
        OnPropertyChanged("Count");
        OnPropertyChanged("Item[]");
    }

    public override void Insert(int index, UIElement element)
    {
        base.Insert(index, element);
        var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, element, index);
        OnCollectionChanged(args);
        OnPropertyChanged("Count");
        OnPropertyChanged("Item[]");
    }

    public override void Remove(UIElement element)
    {
        int index = IndexOf(element);
        if (index >= 0)
        {
            RemoveAt(index);
            var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, element, index);
            OnCollectionChanged(args);
            OnPropertyChanged("Count");
            OnPropertyChanged("Item[]");
        }
    }

    public override UIElement this[int index]
    {
        get
        {
            return base[index];
        }
        set
        {
            base[index] = value;
            var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, value, index);
            OnCollectionChanged(args);
            OnPropertyChanged("Item[]");
        }
    }

    public event NotifyCollectionChangedEventHandler CollectionChanged;
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        var handler = CollectionChanged;
        if (handler != null)
            handler(this, e);
    }

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

MyUniformGrid

public class MyUniformGrid : UniformGrid
{
    protected override UIElementCollection CreateUIElementCollection(FrameworkElement logicalParent)
    {
        return new ObservableUIElementCollection(this, logicalParent);
    }
}

XAML

<local:MyUniformGrid x:Name="MyUniformGrid"
     Rows="{Binding RelativeSource={RelativeSource Self}, Path=Children.Count, Converter={StaticResource CountToDimensionConverter}, ConverterParameter=R}"
     Columns="{Binding RelativeSource={RelativeSource Self}, Path=Children.Count, Converter={StaticResource CountToDimensionConverter}, ConverterParameter=C}">
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
    <Button Content="Hello, World!" />
</local:MyUniformGrid>