我已经创建了一个示例应用来检查Observable Dictionary的双向绑定。当调用构造函数时，数据正在使用UI正确地绑定。但之后如果我尝试更新ObservableDictionary，那么Dictionary是获得更新，但UI没有升级。
这是我的主页
public class TestPage : ContentPage
{
public ObservableDictionary<int, string> DataDict = new ObservableDictionary<int, string>();
public TestPage ()
{
this.BindingContext = DataDict;
DataDict.Add(1, "One");
DataDict.Add(2, "two");
DataDict.Add(3, "Three");
var editor = new Entry();
editor.HorizontalOptions = LayoutOptions.FillAndExpand;
editor.SetBinding(Entry.TextProperty,string.Format("[1]"), BindingMode.TwoWay);
var btn = new Button();
btn.Text = "Check";
btn.HorizontalOptions = LayoutOptions.FillAndExpand;
btn.Clicked += Btn_Clicked;
var vertical = new StackLayout();
vertical.Orientation = StackOrientation.Vertical;
vertical.Children.Add(editor);
vertical.Children.Add(btn);
Content = vertical;
}
private void Btn_Clicked(object sender, EventArgs e)
{
DataDict[1] = DataDict[1] + DataDict[2];
}
}
这是我正在尝试使用的ObservableDictionary
[DebuggerDisplay("Count={Count}")]
public class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>,
INotifyCollectionChanged, INotifyPropertyChanged
{
// Internal dictionary that holds values
private readonly IDictionary<TKey, TValue> underlyingDictionary;
bool shouldRaiseNotifications = true;
/// <summary>
/// Event raised for collection change notification
/// </summary>
public event NotifyCollectionChangedEventHandler CollectionChanged;
/// <summary>
/// Event raise for property changes.
/// </summary>
public event PropertyChangedEventHandler PropertyChanged;
/// <summary>
/// Constructor
/// </summary>
public ObservableDictionary()
: this(new Dictionary<TKey, TValue>())
{
}
/// <summary>
/// Constructor that allows different storage initialization
/// </summary>
public ObservableDictionary(IDictionary<TKey, TValue> store)
{
if (store == null)
throw new ArgumentNullException("store");
underlyingDictionary = store;
}
/// <summary>
/// Constructor that takes an equality comparer
/// </summary>
/// <param name="comparer">Comparison class</param>
public ObservableDictionary(IEqualityComparer<TKey> comparer)
: this(new Dictionary<TKey, TValue>(comparer))
{
}
/// <summary>
/// This method turns off notifications until the returned object
/// is Disposed. At that point, the entire dictionary is invalidated.
/// </summary>
/// <returns>IDisposable</returns>
public IDisposable BeginMassUpdate()
{
return new MassUpdater(this);
}
/// <summary>
/// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <param name="key">The object to use as the key of the element to add.
/// </param><param name="value">The object to use as the value of the element to add.
/// </param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.
/// </exception><exception cref="T:System.ArgumentException">An element with the same key already exists in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
/// </exception>
public void Add(TKey key, TValue value)
{
var item = new KeyValuePair<TKey, TValue>(key, value);
underlyingDictionary.Add(item);
OnNotifyAdd(item);
}
/// <summary>
/// Adds an item to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <param name="item">The object to add to the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item)
{
underlyingDictionary.Add(item);
OnNotifyAdd(item);
}
/// <summary>
/// Removes all items from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
public void Clear()
{
underlyingDictionary.Clear();
OnNotifyReset();
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key.
/// </summary>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the key; otherwise, false.
/// </returns>
/// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.
/// </exception>
public bool ContainsKey(TKey key)
{
return underlyingDictionary.ContainsKey(key);
}
/// <summary>
/// Copies the elements of the <see cref="T:System.Collections.Generic.ICollection`1"/> to an <see cref="T:System.Array"/>, starting at a particular <see cref="T:System.Array"/> index.
/// </summary>
/// <param name="array">The one-dimensional <see cref="T:System.Array"/> that is the destination of the elements copied from <see cref="T:System.Collections.Generic.ICollection`1"/>. The <see cref="T:System.Array"/> must have zero-based indexing.
/// </param><param name="arrayIndex">The zero-based index in <paramref name="array"/> at which copying begins.
/// </param>
/// <exception cref="T:System.ArgumentNullException"><paramref name="array"/> is null.</exception>
/// <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="arrayIndex"/> is less than 0.</exception>
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
underlyingDictionary.CopyTo(array, arrayIndex);
}
/// <summary>
/// Returns an enumerator that iterates through the collection.
/// </summary>
/// <returns>
/// A <see cref="T:System.Collections.Generic.IEnumerator`1"/> that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>1</filterpriority>
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
return underlyingDictionary.GetEnumerator();
}
/// <summary>
/// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <returns>
/// true if the element is successfully removed; otherwise, false. This method also returns false if <paramref name="key"/> was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
/// <param name="key">The key of the element to remove.
/// </param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.
/// </exception><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
/// </exception>
public bool Remove(TKey key)
{
TValue local = underlyingDictionary[key];
bool flag = underlyingDictionary.Remove(key);
OnNotifyRemove(new KeyValuePair<TKey, TValue>(key, local));
return flag;
}
/// <summary>
/// Removes the first occurrence of a specific object from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// true if <paramref name="item"/> was successfully removed from the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false. This method also returns false if <paramref name="item"/> is not found in the original <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
/// <param name="item">The object to remove from the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </param><exception cref="T:System.NotSupportedException">The <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </exception>
bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
{
bool flag = underlyingDictionary.Remove(item);
if (flag)
OnNotifyRemove(item);
return flag;
}
/// <summary>
/// Determines whether the <see cref="T:System.Collections.Generic.ICollection`1"/> contains a specific value.
/// </summary>
/// <returns>
/// true if <paramref name="item"/> is found in the <see cref="T:System.Collections.Generic.ICollection`1"/>; otherwise, false.
/// </returns>
/// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </param>
bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item)
{
return underlyingDictionary.Contains(item);
}
/// <summary>
/// Returns an enumerator that iterates through a collection.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.IEnumerator"/> object that can be used to iterate through the collection.
/// </returns>
/// <filterpriority>2</filterpriority>
IEnumerator IEnumerable.GetEnumerator()
{
return underlyingDictionary.GetEnumerator();
}
/// <summary>
/// Gets the value associated with the specified key.
/// </summary>
/// <returns>
/// true if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/> contains an element with the specified key; otherwise, false.
/// </returns>
/// <param name="key">The key whose value to get.
/// </param><param name="value">When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the <paramref name="value"/> parameter. This parameter is passed uninitialized.
/// </param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.
/// </exception>
public bool TryGetValue(TKey key, out TValue value)
{
return underlyingDictionary.TryGetValue(key, out value);
}
/// <summary>
/// Gets the number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </summary>
/// <returns>
/// The number of elements contained in the <see cref="T:System.Collections.Generic.ICollection`1"/>.
/// </returns>
public int Count
{
get { return underlyingDictionary.Count; }
}
/// <summary>
/// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
/// </summary>
/// <returns>
/// true if the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only; otherwise, false.
/// </returns>
public bool IsReadOnly
{
get { return false; }
}
/// <summary>
/// Gets or sets the element with the specified key.
/// </summary>
/// <returns>
/// The element with the specified key.
/// </returns>
/// <param name="key">The key of the element to get or set.
/// </param><exception cref="T:System.ArgumentNullException"><paramref name="key"/> is null.
/// </exception><exception cref="T:System.Collections.Generic.KeyNotFoundException">The property is retrieved and <paramref name="key"/> is not found.
/// </exception><exception cref="T:System.NotSupportedException">The property is set and the <see cref="T:System.Collections.Generic.IDictionary`2"/> is read-only.
/// </exception>
public TValue this[TKey key]
{
get { return underlyingDictionary[key]; }
set
{
if (underlyingDictionary.ContainsKey(key))
{
var originalValue = underlyingDictionary[key];
underlyingDictionary[key] = value;
OnNotifyReplace(new KeyValuePair<TKey, TValue>(key, value), new KeyValuePair<TKey, TValue>(key, originalValue));
}
else
{
underlyingDictionary[key] = value;
OnNotifyAdd(new KeyValuePair<TKey, TValue>(key, value));
}
}
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
public ICollection<TKey> Keys
{
get { return underlyingDictionary.Keys; }
}
/// <summary>
/// Gets an <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </summary>
/// <returns>
/// An <see cref="T:System.Collections.Generic.ICollection`1"/> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2"/>.
/// </returns>
public ICollection<TValue> Values
{
get { return underlyingDictionary.Values; }
}
/// <summary>
/// This is used to notify insertions into the dictionary.
/// </summary>
/// <param name="item">Item</param>
protected void OnNotifyAdd(KeyValuePair<TKey, TValue> item)
{
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item));
OnPropertyChanged(new PropertyChangedEventArgs(nameof(Count)));
OnPropertyChanged(new PropertyChangedEventArgs(item.Key.ToString()));
}
/// <summary>
/// This is used to notify removals from the dictionary
/// </summary>
/// <param name="item">Item</param>
protected void OnNotifyRemove(KeyValuePair<TKey, TValue> item)
{
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item));
OnPropertyChanged(new PropertyChangedEventArgs(nameof(Count)));
OnPropertyChanged(new PropertyChangedEventArgs(item.Key.ToString()));
}
/// <summary>
/// This is used to notify replacements in the dictionary
/// </summary>
/// <param name="newItem">New item</param>
/// <param name="oldItem">Old item</param>
protected void OnNotifyReplace(KeyValuePair<TKey, TValue> newItem, KeyValuePair<TKey, TValue> oldItem)
{
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, newItem, oldItem));
OnPropertyChanged(new PropertyChangedEventArgs(oldItem.Key.ToString()));
}
/// <summary>
/// This is used to notify that the dictionary was completely reset.
/// </summary>
protected void OnNotifyReset()
{
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
OnPropertyChanged(new PropertyChangedEventArgs(nameof(Count)));
}
/// <summary>
/// Raises the <see cref="E:System.Collections.ObjectModel.ObservableCollection`1.CollectionChanged"/> event with the provided arguments.
/// </summary>
/// <param name="e">Arguments of the event being raised.</param>
protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
{
if (shouldRaiseNotifications == false)
return;
CollectionChanged?.Invoke(this, e);
}
/// <summary>
/// Raises the property change notification
/// </summary>
/// <param name="e">Property event args.</param>
protected virtual void OnPropertyChanged(PropertyChangedEventArgs e)
{
if (shouldRaiseNotifications == false)
return;
PropertyChanged?.Invoke(this, e);
}
//IEnumerator IEnumerable.GetEnumerator()
//{
// throw new NotImplementedException();
//}
/// <summary>
/// IDisposable class which turns off updating
/// </summary>
class MassUpdater : IDisposable
{
readonly ObservableDictionary<TKey, TValue> parent;
public MassUpdater(ObservableDictionary<TKey, TValue> parent)
{
this.parent = parent;
parent.shouldRaiseNotifications = false;
}
~MassUpdater()
{
Debug.Assert(true, "Did not dispose returned object from ObservableDictionary.BeginMassUpdate!");
}
public void Dispose()
{
parent.shouldRaiseNotifications = true;
parent.OnNotifyReset();
}
}
}
任何人都可以告诉我在更新词典时如何更新UI。我必须将它用作双向数据绑定。