词典使用是自定义键，但键始终不相等

Question

I am using RTBTextPointer as custom key in dictionary...

   Init.SpintaxEditorPropertyMain.SpintaxListDict = new Dictionary<RTBTextPointer, SpintaxEditorProperties.SpintaxMappedValue>(new RTBTextPointerComparer());

I worte this RTBTextPointer, and RTBTextPointerComparer classes in class library and using this in different wpf projects,

 if (Init.SpintaxEditorPropertyMain.SpintaxListDict.ContainsKey(_index) == false)
        {
            Init.SpintaxEditorPropertyMain.SpintaxListDict.Add(_index,_SpintaxMappedVal);
        }

everytime containsKey returns false, even it contains, so duplication entry occurs in dictionary.. is anything wrong in my "GetHashCode()"

    public class RTBTextPointer
    {
    static int _row;
    static int _column;

    public int Row
    {
        get
        {
            return _row;
        }
        set
        {
            _row = value;
        }
    }
    public int Column
    {
        get
        {
            return _column;
        }
        set
        {
            _column = value;
        }
    }

}

public class RTBTextPointerComparer : IEqualityComparer<RTBTextPointer>
{
    public bool Equals(RTBTextPointer x, RTBTextPointer y)
    {         
        bool result = int.Equals(x.Column, y.Column) && (int.Equals(x.Row, y.Row));

        return result;
    }

    public int GetHashCode(RTBTextPointer obj)
    {
        var result = 0;
        int hCode = obj.Column ^ obj.Row;
        result = hCode.GetHashCode();
        return result;
    }
}

Please help me Thanks in advance

Answer 1

Your problem probably stems from the following declarations in RTBTextPointer :

static int _row;
static int _column;

These don't do what I think you're intending. They should be

private int _row; 
private int _column; 

As it is right now, these variables reference static members of RTBTextPointer . This means that any access of them will access or mutate the static members of it. static members are accessible to every instance of a type. If you make them private , they will apply per instance, which I believe is your intent.

Once that is corrected, I would reconsider the design of your class, at least if you intent to use it as a key in a Dictionary . RTBTextPointer should be immutable, or atleast the fields and properties that GetHashCode() depends on. Here's why:

When you add a object as a key to a dictionary, it's associated value is placed in a hash bucket , which is simply some data structure associated with a hash code. Assume we have some arbitrary key RTBTextPointer with Row = 2 and Column = 2 and a value of "Foo". It's GetHashCode would be 0 (2 XOR 2).

Hash Key                  Value
0    RTBTextPointer(2,2)  Foo

Right now, a call to Dictionary.ContainsKey() would return true looking for RTBTextPointer(2,2) . Now consider if this RTBTextPointer changed to have a Row = 4 . It's hash code would now be 6 (4 XOR 2). The call to Dictionary.ContainsKey() would now be false, and the value Foo would be inaccessible because the key has a hash code that depends upon mutable state.

As a final note, I would consider overriding the Equals() and GetHashCode() methods of object .

Answer 2

I don't think you need to create a separate comparer. Just overriding Equals and GetHashCode should suffice.

Also, if you have very simple properties like that, you could switch to auto properties

public class RTBTextPointer
{
    public int Row
    {
        get;
        set;
    }
    public int Column
    {
        get;
        set;
    }
    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj))
        {
            return false;
        }
        if (ReferenceEquals(this, obj))
        {
            return true;
        }
        var other = obj as RTBTextPointer;
        if (other == null)
        {
            return false;
        }
        return other.Row == Row && other.Column == Column;
    }
    public override int GetHashCode()
    {
        unchecked
        {
            // 397 or some other prime number
            return (Row * 397) ^ Column;
        }
    }
}

See unchecked for more information about that.

If you have more than two properties, and if those properties could be null, the GetHashCode might look like this:

unchecked
{
    var result = 0;
    result = (result * 397) ^ (Prop1 != null ? Prop1.GetHashCode() : 0);
    result = (result * 397) ^ (Prop2 != null ? Prop2.GetHashCode() : 0);
    result = (result * 397) ^ (Prop3 != null ? Prop3.GetHashCode() : 0);
    result = (result * 397) ^ (Prop4 != null ? Prop4.GetHashCode() : 0);
    // ...
    return result;
}