绑定到Children.Count [英] Binding to Children.Count

问题描述

我使用的形式结合

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

尽管在XAML中添加的孩子，当我在转炉突破，该值始终为0。

Despite adding the children in xaml, when I break in the converter, the value is always 0.

我认为正在发生的是，孩子们不会添加后才这种结合被调用。

What I assume is going on is that the children are not added until after this binding is called.

我也假设结合被打破后，它被称为曾经因为.Count之间是一个只读属性（我有，我必须在属性添加一个空二传手维持约束力和愚弄WPF之前类似的问题）因此绑定儿童一旦被添加不更新。

I also assume that the binding is broken after it's been called once because .Count is a readonly property (I've had a similar problem before where I had to add an empty setter in the property to maintain the binding and fool WPF) hence the binding not updating once children are added.

不过，我卡在那里你拿出解决问题的办法，并使其发挥作用... = /

However, I'm stuck on the bit where you come up with a solution for the problem and make it work... =/

<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，
RABIT

Thanks, Rabit

推荐答案

这是因为 UIElementCollection （即儿童的类型属性）不会引发通知时一个新的项目添加或删除，因此不会刷新的结合

That's because UIElementCollection (the type of the Children property) doesn't raise notifications when a new item is added or removed, so the binding isn't refreshed

您可以，但是，创建自己的定制 UniformGrid ，并覆盖 CreateUIElementCollection 属性创建的实例自定义集合继承 UIElementCollection 和农具 INotifyCollectionChanged 。

You could, however, create your own custom UniformGrid, and override the CreateUIElementCollection property to create an instance of a custom collection that inherits UIElementCollection and implements INotifyCollectionChanged.

下面是一个基本的实现：

Here's a basic implementation :

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>

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