Question

在XAML中（特别是在通用Windows平台上）我可以使用索引器的属性路径表示法将数据绑定到索引属性。

e.g。给定类型Dictionary<string,string>的数据源，我可以绑定到索引属性，如下所示：

<TextBlock Text="{Binding Dictionary[Property]}"/>

在上文中，TextBlock的DataContext被设置为具有字典属性的对象，如下所示：

public class DataObject
{
    public Dictionary<string,string> Dictionary { get; } = new Dictionary<string,string> {["Property"]="Value"};
}

我的问题是，是否可以在不使用索引器表示法的情况下绑定到索引属性，而是使用标准属性绑定的语法？

即

<TextBlock Text="{Binding Dictionary.Property}"/>

从我最初的测试来看，这似乎不起作用。有一种简单的方法可以使它工作吗？我想使用具有索引属性的数据源对象（在本例中类似于Dictionary，但可能只是一个简单的对象）。我不想使用动态对象。

Answer 1

没有语法可以做你想要的，我害怕。标准属性绑定的语法适用于标准属性，例如

<TextBlock Text="{Binding Dictionary.Count}" />

...将绑定到字典的Count属性（或任何对象）。你需要它们括号......

修改

如果你真的讨厌括号，我能找到的最接近的东西就是使用带参数的转换器。例如：

public class MyConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, string language) { IDictionary<string, string> dictionary = value as IDictionary<string, string>; string dictionaryValue; if (dictionary != null && dictionary.TryGetValue(parameter as string, out dictionaryValue)) { return dictionaryValue; } return value; } public object ConvertBack(object value, Type targetType, object parameter, string language) { throw new NotSupportedException(); } }

XAML：

<Page x:Class="UWP.MainPage" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:uwp="using:UWP"> <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> <Grid.Resources> <uwp:MyConverter x:Key="MyConverter" /> </Grid.Resources> <Grid.DataContext> <uwp:DataObject /> </Grid.DataContext> <TextBlock Text="{Binding Dictionary, ConverterParameter=Property1, Converter={StaticResource MyConverter}}" /> </Grid> </Page>

......这是一种迂回的方式，最终会出现比括号更难读的东西。

Answer 2

很久以前，Windows 8应用程序模板中就有这个ObservableDictionary类，它可以满足您的需求。它不是Dictionary<string, string>，但是您可以将Dictionary中的值复制到ObservableDictionary

用法

在ViewModel中声明一个ObservableDictionary属性，然后像通常的属性一样绑定到其索引器：

using System;
using System.Collections.Generic;
using System.Linq;
using Windows.Foundation.Collections;

namespace MyApp
{
    public class ObservableDictionary : IObservableMap<string, object>
    {
        private class ObservableDictionaryChangedEventArgs : IMapChangedEventArgs<string>
        {
            public ObservableDictionaryChangedEventArgs(CollectionChange change, string key)
            {
                this.CollectionChange = change;
                this.Key = key;
            }

            public CollectionChange CollectionChange { get; private set; }
            public string Key { get; private set; }
        }

        private Dictionary<string, object> _dictionary = new Dictionary<string, object>();
        public event MapChangedEventHandler<string, object> MapChanged;

        private void InvokeMapChanged(CollectionChange change, string key)
        {
            var eventHandler = MapChanged;
            if (eventHandler != null)
            {
                eventHandler(this, new ObservableDictionaryChangedEventArgs(change, key));
            }
        }

        public void Add(string key, object value)
        {
            this._dictionary.Add(key, value);
            this.InvokeMapChanged(CollectionChange.ItemInserted, key);
        }

        public void Add(KeyValuePair<string, object> item)
        {
            this.Add(item.Key, item.Value);
        }

        public bool Remove(string key)
        {
            if (this._dictionary.Remove(key))
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
                return true;
            }
            return false;
        }

        public bool Remove(KeyValuePair<string, object> item)
        {
            object currentValue;
            if (this._dictionary.TryGetValue(item.Key, out currentValue) &&
                Object.Equals(item.Value, currentValue) && this._dictionary.Remove(item.Key))
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, item.Key);
                return true;
            }
            return false;
        }

        public virtual object this[string key]
        {
            get
            {
                return this._dictionary[key];
            }
            set
            {
                this._dictionary[key] = value;
                this.InvokeMapChanged(CollectionChange.ItemChanged, key);
            }
        }

        public void Clear()
        {
            var priorKeys = this._dictionary.Keys.ToArray();
            this._dictionary.Clear();
            foreach (var key in priorKeys)
            {
                this.InvokeMapChanged(CollectionChange.ItemRemoved, key);
            }
        }

        public ICollection<string> Keys
        {
            get { return this._dictionary.Keys; }
        }

        public bool ContainsKey(string key)
        {
            return this._dictionary.ContainsKey(key);
        }

        public bool TryGetValue(string key, out object value)
        {
            return this._dictionary.TryGetValue(key, out value);
        }

        public ICollection<object> Values
        {
            get { return this._dictionary.Values; }
        }

        public bool Contains(KeyValuePair<string, object> item)
        {
            return this._dictionary.Contains(item);
        }

        public int Count
        {
            get { return this._dictionary.Count; }
        }

        public bool IsReadOnly
        {
            get { return false; }
        }

        public IEnumerator<KeyValuePair<string, object>> GetEnumerator()
        {
            return this._dictionary.GetEnumerator();
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return this._dictionary.GetEnumerator();
        }

        public void CopyTo(KeyValuePair<string, object>[] array, int arrayIndex)
        {
            int arraySize = array.Length;
            foreach (var pair in this._dictionary)
            {
                if (arrayIndex >= arraySize) break;
                array[arrayIndex++] = pair;
            }
        }
    }
}

Answer 3

class DictionaryXamlWrapper : DynamicObject, INotifyPropertyChanged
{
    #region PropertyChangedFunctional
    public void OnPropertyChanged([CallerMemberName] string aProp = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(aProp));
    }

    public event PropertyChangedEventHandler PropertyChanged;
    #endregion

    Dictionary<string, object> members = new Dictionary<string, object>();

    // установка свойства
    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        members[binder.Name] = value;
        OnPropertyChanged(binder.Name);
        return true;
    }
    // получение свойства
    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        result = null;
        if (members.ContainsKey(binder.Name))
        {
            result = members[binder.Name];
            return true;
        }

        return false;
    }
}

当然，如果不需要，可以删除INotifyPropertyChanged函数。

以及所需的用法

<TextBlock Text="{Binding DictionaryXamlWrapper.TestField}"/>

是否可以使用与标准属性相同的属性路径语法绑定到xaml中的索引属性？

3 个答案:

用法