I have implemented a equality comparer in below manner.
class BoxEqualityComparer : IEqualityComparer<Box>
{
public bool Equals(Box b1, Box b2)
{
if (b2 == null && b1 == null)
return true;
else if (b1 == null | b2 == null)
return false;
else if(b1.Height == b2.Height && b1.Length == b2.Length
&& b1.Width == b2.Width)
return true;
else
return false;
}
public int GetHashCode(Box bx)
{
int hCode = bx.Height ^ bx.Length ^ bx.Width;
return hCode.GetHashCode();
}
}
Then I have created a Dictionary
, in that I will add some values. So here it will compare object based on it's properties (height, width, length). I am getting the expected output. But I am wondering about the execution of GetHashCode
method. I put a breakpoint in there, but I am unable to debug it. My question is when does GeHashCode
method will be executed and how many times?
class Example
{
static void Main()
{
BoxEqualityComparer boxEqC = new BoxEqualityComparer();
var boxes = new Dictionary<Box, string>(boxEqC);
var redBox = new Box(4, 3, 4);
AddBox(boxes, redBox, "red");
var blueBox = new Box(4, 3, 4);
AddBox(boxes, blueBox, "blue");
var greenBox = new Box(3, 4, 3);
AddBox(boxes, greenBox, "green");
Console.WriteLine();
Console.WriteLine("The dictionary contains {0} Box objects.",
boxes.Count);
}
private static void AddBox(Dictionary<Box, String> dict, Box box, String name)
{
try {
dict.Add(box, name);
}
catch (ArgumentException e) {
Console.WriteLine("Unable to add {0}: {1}", box, e.Message);
}
}
}
public class Box
{
public Box(int h, int l, int w)
{
this.Height = h;
this.Length = l;
this.Width = w;
}
public int Height { get; set; }
public int Length { get; set; }
public int Width { get; set; }
public override String ToString()
{
return String.Format("({0}, {1}, {2})", Height, Length, Width);
}
}
Add(key, value) calls the insert method, which in turn will always calculate a hash code via
int hashCode = comparer.GetHashCode(key) & 0x7FFFFFFF;
So in other words, each call to Dictionary.Add should always trigger a calculation of the key's hash via the IEqualityComparer you provided.
As for your example code, this works fine for me, VS 2015 does break at BoxEqualityComparer.GetHashCode() for me.
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