Detailed introduction to C# container classes, interfaces, and performance

1 indexer

　[]The declared variable must be of fixed length, that is, the length is static; object[] objectArray = new object[10] ;
objectArray is shallow copy, that is, only assign an address value to it in memory. At this time, each item is a null reference;

　Application examples

     AdjustablePanel[] adjustPanelArrays = new AdjustablePanel[12];     
     foreach (Control ultraControl in this.Controls)
            {                if (ultraControl.GetType() == typeof(UltraGrid) ||
                 ultraControl.GetType() == typeof(UltraChart) ||   ultraControl.GetType() == typeof(Panel))
                {                //adjustPanelArrays[index]此时为null，因此会出现null引用bug
                    adjustPanelArrays[index].Controls.Add(ultraControl); 
                }
            }

2 Array

Provides Create, Operation, Search and Sort methods of arrays and thus serves as the base class for all arrays in the common language runtime. The length is fixed and cannot be dynamically increased on demand; Array is an abstract class and cannot be created using new Array; GetValue returns the object type.

            Array myArray = Array.CreateInstance(typeof(int),3);
            myArray.SetValue(1,0);
            myArray.SetValue(2,1);
            myArray.SetValue(3,2);            //GetValue返回的是object类型，需要进行类型提升为int
            int val2 = (int)myArray.GetValue(2);

3 ArrayList

Implement the IList interface using an array whose size can be dynamically increased on demand, and is for any type.

            ArrayList al = new ArrayList();
            ArrayList arrayList = new ArrayList();
            al.Add("qaz");
            al.Add(1);
            al.Add(new List<object>());            
            string str = (string)al[0];            
            int intval = (int)al[1];
            List<object> objs = (List<object>)al[2];

Summary
　 [], The length of Array needs to be known before compilation, it is static, and the type needs to be uniquely determined. Array is an abstract class, and Array is required to create it. CreateInstance();
　 The length of ArrayList is unknown at compile time, it is dynamic, and the added elements can be of different types.

4 List-APIs

4-1 Introduction

List is a generic class that implements the interface IList, The external interface is displayed by using a dynamically adjusted array internally.

4-2 Add elements

Implement adding an element

Add(obj)

Add elements to the list in batches:

AddRange(objList)

Example:

        private List<int> intList = new List<int>();        public void AddApi()
        {
            intList.Add(10); //添加1个元素
            intList.AddRange(new List<int>() { 5, 1, 1, 2, 2, 3 }); //批量添加元素
        }

Insert an element in the collection at the specified index

void Insert(int index, T item);

void InsertRange(int index, IEnumerable《T》 collection)

4-3 Remove the element

Assume that intList is a List type, and the initial value is {10,5,1,1, 2,2,3}. Execution:

intList.Remove(1);

Remove the first occurrence of a specific object from the intList. After removing element 1, intList = {10,5,1,2,2,3};

Remove a certain range of elements:

intList.RemoveRange(0, 2);

intList = {2,2,3 };

After removing all duplicate elements: intList = {3};

            intList.RemoveAll(removeDuplicateElements); 
            intList.RemoveAll(i =>
            {                List<int> elementList = intList.FindAll(r => r.Equals(i));                if (elementList != null && elementList.Count > 1)                    return true;                return false;
            });

When judging whether an element exists above, such as when removing an element, equality needs to be used Comparators. If type T implements the IEquatableLet’s look at an example of implementing an interface that is not the default comparator:

    public class MyObject
    {        public int Value { get; set; }        
    public MyObject(int value)
        {            this.Value = value;
        }
    }    //实现接口IEquatable<MyObject>
    public class MyObjectCollection : IEquatable<MyObject>
    {        private List<MyObject> _myObjects = new List<MyObject>()
        {            new MyObject(3),            
        new MyObject(4),            
        new MyObject(3),            
        new MyObject(2),           
         new MyObject(3)
        };        //删除所有重复的元素
        public void RemoveDuplicates()
        {
            _myObjects.RemoveAll(Equals); 
        }        public List<MyObject> MyObjects
        {            get
            {                return _myObjects;
            }
        } 

        public bool Equals(MyObject other)
        {
            MyObject duplicate = _myObjects.Find(r => r.Value == other.Value);            
            if (duplicate != null && duplicate!=other)                
            return true;            
            return false;
        }
    }

Equals(object) is implemented here, but Remove(test) fails temporarily, and we will find out the reason later.

4-4 Find elements

Determine whether an element is in the List.

bool Contains(obj)

Determines whether it contains elements that match the conditions defined by the specified predicate.

bool Exists(Predicate<T> match)

Search for elements that match the conditions defined by the specified predicate and return the first matching element.

T Find(Predicate<T> match)

Retrieves all elements that match the conditions defined by the specified predicate.

List<T> FindAll(Predicate<T> match)

Search for elements that match the conditions defined by the specified predicate and return the zero-based index of the first matching element

int FindIndex(Predicate<T> match)

Search for elements that match the conditions defined by the specified predicate of elements and returns the zero-based index of the first occurrence in the range of elements from the specified index to the last element.

int FindIndex(int startIndex, Predicate<T> match)

Search for elements that match the conditions defined by the specified predicate and return the zero-based index of the first occurrence in a range of elements starting at the specified index and containing the specified number of elements

int FindIndex(int startIndex, int count, Predicate<T> match)

T FindLast(Predicate<T> match)

int FindLastIndex(Predicate<T> match)

int FindLastIndex(int startIndex, Predicate<T> match)

int FindLastIndex(int startIndex, int count, Predicate<T> match)

Searches the specified object and returns the zero-based index of the first match

int IndexOf(T item)

Searches the specified object and returns the first match in the range of elements from the specified index to the last element The zero-based index of the item

int IndexOf(T item, int index)

int IndexOf(T item, int index, int count)

Searches the specified object and returns the zero-based index of the last matching item.

int LastIndexOf(T item)

int LastIndexOf(T item, int index)

int LastIndexOf(T item, int index, int count)

4-5 Binary Search

Use the default comparator to search for an element in the entire

sorted

List and return the zero-based index of the element.

 int BinarySearch(T item);

Searches the entire sorted list for an element using the specified comparator and returns the zero-based index of the element.

int BinarySearch(T item, IComparer<T> comparer)

int BinarySearch(int index, int count, T item, IComparer<T> comparer)

4-6 SortingUse the default comparator to sort the elements in the entire List.

void Sort()

Use the specified System.Comparison to sort the elements in the entire List.

void Sort(Comparison<T> comparison)

Use the specified comparator to sort the elements in the List.

void Sort(IComparer<T> comparer)

void Sort(int index, int count, IComparer<T> comparer)

4-7 Performance analysis

OperationAddO(1) or O(n)O(n)O(n)O( 1)O(nlogn), worst case O(n^2)O(n)

Time complexity

Insert

Remove

GetAnItem

Sort

Find

4-8 附使用陷阱点：

1 list.Min() 和 list.Max() 和 Average()等Linq方法，当list元素个数为0，则会出现“序列不包含任何元素”的异常。

2 object.ToString() 使用前要检测object是否为null。

3 Foreach遍历时，迭代器是不允许增加或删除的。例如：  

 public List<MDevice> GetNormalDevices(List<MDevice> devices)
    {
        rtnDevices = devices;        foreach (var device in devices)
        {            var tmpdevices = bslMDevice.GetMDeviceByDeviceCode(device.DeviceCode);            
        if (!devices[0].IsNormal)
            {            //这是非法的，因为移除rtnDevices列表的一个元素，等价于移除devices列表。
                rtnDevices.Remove(device); 
            }
        }
    }

5 SortedList

5-1 SortedList简介

Sorted表明了它内部实现自动排序，List表明了它有点像List，可以通过index访问集合中的元素。

5-2 内部实现机理

一个SortedList对象内部维护了2个数组，以此来存储元素，其中一个数组用来存放键（keys），另一个存放键关联的值（values）。每一个元素都是键值对（key/value pair）。key不能是null，value可以。

5-3 总结API

5-3-1 Capacity

一个SortedList对象的容量是SortedList能容纳的元素数，这个值是动态变化，自动调整的。如下所示：

SortedList mySL = new SortedList();
mySL.Add("Third", "!");
mySL.Add("Second", "World");
mySL.Add("First", "Hello");
Console.WriteLine( "mySL" );
Console.WriteLine( "  Capacity: {0}", mySL.Capacity );

此时Capacity: 16

如果添加到mySL中的元素增多，相应的Capacity会相应的自动变大。

5-3-2 访问元素

通过index访问

SortedList对象要想通过index访问，需要使用构造函数SortedList() 或 SortedList(IComparer icompared)。

SortedList sortedList = new SortedList();
sortedList.Add(3,"gz");
sortedList.Add(9, "lhx");
sortedList.Add(3, "gz");object getByIndex = sortedList.GetByIndex(2);

通过key访问

SortedList对象要想通过key访问，需要使用带有TKey,TValue的泛型构造函数。

SortedList<int,string> sortedList = new SortedList<int,string>();
sortedList.Add(3,"gz");
sortedList.Add(9, "lhx");object getByIndex = sortedList[3];

5-3-3排序

SortedList有一种默认的比较顺序，比如下面的代码：

SortedList<int,string> sortedList = new SortedList<int,string>();
sortedList.Add(9,"gz");
sortedList.Add(3, "lhx");

结果是 sortedList中第一个对是3,”lhx”

如果不想按照默认的排序顺序，需要自己在构造时定制一种排序顺序，如下面的代码：

实现排序接口

新建一个私有排序类，实现接口IComparer

private class ImplementICompare: IComparer<int>
  {      public int Compare(int x, int y)
      {          return x < y ? 1 : -1;
      }
  }

构造SortedList

ImplementICompare impleCompare = new ImplementICompare();
SortedList<int, string> sortedList = new SortedList<int, string>(impleCompare);
sortedList.Add(9,"gz");
sortedList.Add(3, "lhx");

按照键从大到小的顺序排序，结果是 sortedList中第一个对是9,”gz”

5-3-4 添加元素

用add接口实现添加某个元素到集合中，不允许重复添加相同键。

SortedList<int,string> sortedList = new SortedList<int,string>();
sortedList.Add(9,"gz");
sortedList.Add(3, "lhx");

5-3-5 移除元素

移除集合中指定元素Remove(object removedElement)；指定index处移除元素RemoveAt(int index)。

Remove(object)

SortedList mySL = new SortedList();
mySL.Add( "3c", "dog" );
mySL.Add( "2c", "over" );
mySL.Add( "3a", "the" );
mySL.Add( "3b", "lazy" );   
mySL.Remove( "3b" ); //sucessful to remove

SortedList<int, string> sortedList = new SortedList<int, string>();
sortedList.Add(9,"gz");
sortedList.Add(3, "lhx");bool removedFlag = sortedList.Remove(3); //true

ImplementICompare impleCompare = new ImplementICompare();
SortedList<int, string> sortedList = new SortedList<int, string>(impleCompare);
sortedList.Add(9,"gz");
sortedList.Add(3, "lhx");bool removedFlag = sortedList.Remove(3); //false

这是需要注意的一个地方，构造器带有impleCompare实现了排序接口时，好像不能移除某个元素，需要待确认。

RemoveAt(int index)

SortedList sorted = new SortedList();
sorted.Add(9, "gz");
sorted.Add(3, "lhx");
sortedList.RemoveAt(1); //在排序后的位置移除，sortedList的一个对的键 为3，第二个对的键为9，因此移除了9这个键值对

5-4 性能

一个SortedList的操作相比Hashtable对象是要慢些的，由于它实现了排序功能。但是，SortedList提供了访问的方便性，由于既可以通过index，也可以通过key去访问元素。

6 .net容器相关接口

接口	描述
IEnumerable	实现foreach语句需要实现此接口，接口方法GetEnumerator返回枚举器。
ICollection	方法：Count属性，CopyTo(Array),Add, Remove, Clear
IList	定义了indexer,Insert, RemoveAt方法，继承ICollection
ISet	方法：求并集，交集，继承于ICollection
IDictionary	有key和value的集合实现
ILookup	类似上，允许multiple values with one key.
IComparer	comparer实现，排序比较的规则
IEqualityComparer	对象be compared for equality另一个对象
IProducerConsumerCollection	thread-safe collection classes

7 Interface UML

8 Time complexity of each container

##HashSetO(1) or O(n)O(1) or O(n)O(1)Not applicableNot applicableNot applicableLinkedListO(1)O(1)O(1) O(n)Not applicableO(n)DictionaryO(1)or O(n)Not applicableO(1)O(1)Not applicableNot applicableSortedDictionaryO(logn)Not applicableO(logn)O (logn)Not applicableNot applicableSortedListO(logn)Not applicableO(n)O(logn)Not applicableNot applicable

set Type	Add	Insert	Remove	Item	Sort	Find
List	O(1) or O(n)	O(n)	O(n)	O(1)	O(nlogn)	O(n)
Stack	O(1) or O(n)	Not applicable	pop() O(1)	Not applicable	Not applicable	Not applicable
Queue	O(1) or O(n)	Not applicable	O(1)	Not applicable	Not applicable	Not applicable

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