如何获取集合的父对象？

Question

在 C# 中，如果我有一个包含集合的对象，是否可以检索包含该集合的对象？

这是一个例子：

public class TestObject
{
    public string name { get; set; }
    public TestObjectCollection testObjects{ get; set; } 
}

TestObjectCollection集合继承自CollectionBase，是TestObjects的集合。

这是一个示例实现：

创建了一个 TestObject，名称为 "Test1"
名称为 "Test1" 的 TestObject 有一个 TestObjectCollection TestObject 名称为 "Test2"

如果我有名字为"Test2"的TestObject，我怎样才能得到名字为"Test1"

的TestObject

谢谢

Answer 1

唯一的方法是在子对象中保留对父对象的引用。您可以在创建子对象时执行此操作：

this.testObjects = new TestObjectCollection(this);

然后在 TestObjectCollection 的构造函数中：

public TestObject ParentObject { get; set; }

public TestObjectCollection(TestObject parent)
{
    ParentObject = parent;
    ...
}

Answer 2

也许你可以这样做:

using System;
using System.Collections.Generic;

public class TestObject
{
    private TestObjectCollection _testObjects;

    public string name { get; set; }
    public TestObjectCollection parentCollection { get; set; }
    public TestObjectCollection testObjects 
    { 
        get
        {
            return _testObjects;
        }
        set 
        {
            _testObjects = value;
            _testObjects.parent = this;
        }
    }
}

public class TestObjectCollection
{
    private List<TestObject> _testObjects;

    public TestObject parent { get; set; }

    public TestObjectCollection()
    {
        _testObjects = new List<TestObject>();
    }

    public void Add(TestObject testObject)
    {
        testObject.parentCollection = this;
        _testObjects.Add(testObject);
    }

    public TestObject this[int i] {
        get {
            return _testObjects[i];
        }
    }
}


public class Test
{
    public static void Main()
    {
        // your code goes here
        TestObject test1 = new TestObject();

        TestObject test2 = new TestObject();

        var collection = new TestObjectCollection();
        collection.Add(test2);
        test1.testObjects = collection;

        if (test2.parentCollection.parent == test1)
        {
            Console.WriteLine("Done");
        }
        else
        {
            Console.WriteLine("Fail");
        }
    }
}

我以List为例

Answer 3

除非您明确地编写父子关系代码（如 Yogesh 的回答），否则无法找到 "the" 父级 - 很大程度上是因为可能有不止一个这样的父级：

public class TestObject
{
    public string name { get; set; }
    public TestObjectCollection testObjects{ get; set; } 
}
public class TestObjectCollection : CollectionBase
{
    public void Add(TestObject to)
    {
        this.List.Add(to);
    }
}
void Main()
{
    TestObjectCollection children = new TestObjectCollection();
    TestObject child = new TestObject { name = "child" };
    children.Add(child);

    TestObject parent = new TestObject { name = "parent", testObjects = children }; 
    TestObject otherParent = new TestObject { name = "otherParent", testObjects = children };   
    TestObject stepParent = new TestObject { name = "stepParent", testObjects = children }; 
    TestObject inLocoParentis = new TestObject { name = "inLocoParentis", testObjects = children };
    // and we can keep going on and on and on ...   
}

Answer 4

如果您不想在构造函数中传递引用，您可以使用静态字典来跟踪 TestObject 实例，并让 TestObjectCollection 以延迟加载的方式从该静态字典中查找它的父项。

例如

public class TestObject
{
    /// <summary>
    /// Keep a list of all the instances of TestObject's that are created.
    /// </summary>
    internal static Dictionary<Guid, TestObject> _collections = new Dictionary<Guid, TestObject>();

    /// <summary>
    /// An ID to uniquely identify an instance of a TestObject
    /// </summary>
    public Guid ID { get; private set; }

    /// <summary>
    /// A reference to the collection which will be set in the constructor
    /// </summary>
    public TestObjectCollection TestObjects { get; private set; }

    public TestObject()
    {
        //generate the unique id
        this.ID = Guid.NewGuid();
        this.TestObjects = new TestObjectCollection();
        //add this testobject to the List of test objects.
        _collections.Add(this.ID, this);
    }

    /// <summary>
    /// Destructor, kill the TestObject from the list of TestObject's.
    /// </summary>
    ~TestObject()
    {
        if (_collections.ContainsKey(this.ID))
        {
            _collections.Remove(this.ID);
        }
    }
}

public class TestObjectCollection : IEnumerable<TestObject>
{
    private List<TestObject> _testObjects = new List<TestObject>();

    public Guid ID { get; private set; }

    public TestObject this[int i]
    {
        get
        {
            return _testObjects[i];
        }
    }

    private TestObject _Parent = null;
    public TestObject Parent
    {
        get
        {
            if (_Parent == null)
            {
                _Parent = TestObject._collections.Values.Where(p => p.TestObjects.ID == this.ID).FirstOrDefault();
            }
            return _Parent;
        }
    }

    public TestObjectCollection()
    {
        this.ID = Guid.NewGuid();
    }

    public void Add(TestObject newObject)
    {
        if (newObject != null)
            _testObjects.Add(newObject);
    }

    public IEnumerator<TestObject> GetEnumerator()
    {
        return _testObjects.GetEnumerator();
    }

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

正在测试...

class Program
{
    static void Main(string[] args)
    {
        TestObject tObject = new TestObject();
        Console.WriteLine("TestObject ID: " + tObject.ID);
        Console.WriteLine("TestObject TestObjectCollection ID: " + tObject.TestObjects.ID);
        Console.WriteLine("TestObject TestObjectCollection Parent ID: " + tObject.TestObjects.Parent.ID);
        Console.WriteLine("Press any key...");

        Console.ReadKey(true);
    }
}

因此，它在 TestObject 的构造函数中为自己提供了一个 GUID ID。然后它创建一个 TestObjectCollection 实例。

在 TestObjectCollection 的构造函数中，它给自己一个 GUID ID。

回到 TestObject 的构造函数中，它将 TestObjects 设置为它刚刚创建的集合，然后将对自身的引用添加到静态的 TestObjects 字典中。它使用 TestObject 的 ID 作为所述字典的键。

然后在 TestObjectCollection 中，它通过使用属性在该静态字典中查找它来获取父集合，该属性在调用它之前不会自行设置（因为您无法在构造函数中确定它，因为TestObject 构造函数尚未添加引用）。

    private TestObject _Parent = null;
    public TestObject Parent
    {
        get
        {
            if (_Parent == null)
            {
                _Parent = TestObject._collections.Values.Where(p => p.TestObjects.ID == this.ID).FirstOrDefault();
            }
            return _Parent;
        }
    }

如何获取集合的父对象？

How can I get a collection's parent object?

c#

collectionbase