c# - 检查对象是否为 ObservableCollection？

Question

我想检查一个值是否属于任何类型的 ObservableCollection 类型，或者不在 C# 中？

例如：我可以检查一个值是否为字符串类型，如下所示：

string value = "value to Check";
bool b = value.GetType().Equals(typeof(string));  // b =true

但是如果我需要检查一个值是否是 ObservableCollection，无论其构成类型如何，我该怎么做？

例如：

ObservableCollection<T> collection = new ObservableCollection<T>();

如果我这样检查

bool b = collection.GetType().Equals(typeof(ObservableCollection<>)); // b=false

如何检查该值是否为收藏？

Answer 1

尝试

bool b = collection.GetType().IsGenericType &&
           collection.GetType().GetGenericTypeDefinition() == typeof(ObservableCollection<>);

Answer 2

你可以像这样检查它：

public static bool IsObservableCollection(object candidate) {
    if (null == candidate) return false;

    var theType = candidate.GetType();
    bool itIs = theType.IsGenericType() && 
        !theType.IsGenericTypeDefinition()) &&
        (theType.GetGenericTypeDefinition() == typeof(ObservableCollection<>));

    return itIs;
}

您还可以获得元素类型：

public static Type GetObservableCollectionElement(object candidate) {
    bool isObservableCollection = IsObservableCollection(candidate);
    if (!isObservableCollection) return null;

    var elementType = candidate.GetType().GetGenericArguments()[0];
    return elementType;
}

编辑

实际上以动态方式使用 ObservableCollection 有点棘手。如果您查看ObservableCollection<T>课程：

ObservableCollection<T> : Collection<T>, INotifyCollectionChanged, INotifyPropertyChanged

您会注意到它扩展Collection<T>并实现了 2 个接口。

因此，由于 everyCollection<T>也是非泛型的IEnumerable，您可以像这样推断动态已知的 ObservableCollection：

object someObject = ...
bool itsAnObservableCollection = IsObservableCollection(someObject);

if (itsAnObservableCollection) {
    IEnumerable elements = someObject as IEnumerable;
    // and try to reason about the elements in this manner
    foreach (var element in elements) { ... }

    INotifyCollectionChanged asCC = someObject as INotifyCollectionChanged;
    INotifyPropertyChanged asPC = someObject as INotifyPropertyChanged;
    // and try to let yourself receive notifications in this manner
    asCC.CollectionChanged += (sender, e) => {
        var newItems = e.NewItems;
        var oldItems = e.OldItems; 
        ...
    };     
    asPC.PropertyChanged += (sender, e) => {
        var propertyName = e.PropertyName;
        ...
    };   

}

Answer 3

根据您的需要，您还可以检查它是否实现INotifyCollectionChanged.

if (someCollection is INotifyCollectionChanged observable)
    observable.CollectionChanged += CollectionChanged;

Answer 4

集合的类型是泛型的，您要测试该类型的泛型定义：

collection.GetType()
  .GetGenericTypeDefinition()
  .Equals(typeof(ObservableCollection<>))