如何在 C# 中使用 SingleOrDefault 创建用于从 Dictionary 查询值的谓词

Question

I have a Dictionary with Key as RectangleF and Value as int. Since, int will have duplicate values, So I cannot use that as key.

Dictionary<RectangleF, int> lnRectTable = new Dictionary<RectangleF, int>();

lnRectTable.Add(new RectangleF(10.6f, 15.86f, 25.0f, 36.55f), 55);
lnRectTable.Add(new RectangleF(15.6f, 15.86f, 25.0f, 36.55f), 55);
lnRectTable.Add(new RectangleF(-36.8f, 15.86f, 25.0f, 36.55f), 150);

So, I want to find value "If Exists" in the Dictionary which matches the following condition.

RectangleF searchRect = new RectangleF(10.7f, 15.86f, 25.0f, 36.55f);

int matchingValue= lnRectTable.SingleOrDefault(
       t => Math.Abs(searchRect .X - t.Key.X) <= 0.1 &&
       Math.Abs(searchRect .Y - t.Key.Y) <= 0.1).Value;

//I will get value as 55. 

But, I want to use this kind of conditional check many times many places in my program. What's the best way to do it. I am not sure, I am thinking of Predicates / Expressions. So that I will more control. If So, How do I do it ?

Thanks in Advance.

Answer 1

You can assign your predicate to a variable or property and then use it everywhere.

Func<RectangleF, RectangleF, bool> expr = 
  (RectangleF searchRect, RectangleF key) => 
     Math.Abs(searchRect.X - key.X) <= 0.1 && Math.Abs(searchRect.Y - key.Y) <= 0.1;

And then:

int matchingValue= lnRectTable.SingleOrDefault(t => expr(searchRect, t.Key)).Value;

Or, if you want to get fancy you can partially-apply the searchRect to your function and then apply that:

Func<RectangleF,bool> search = (RectangleF rect) => expr(searchRect, rect);

And then you can use the simpler syntax:

int matchingValue= lnRectTable.SingleOrDefault(search).Value;