How to define variable as lambda function

问题:

(Lambda function may or may not be what I'm looking for, I'm not sure)

Essentially what I'm trying to accomplish is this:

int areaOfRectangle = (int x, int y) => {return x * y;};

but it gives error: "Cannot convert lambda expression to type 'int' because it is not a delegate type"

The more detailed problem (that really has nothing to do with the question, but I know someone will ask) is:

I have several functions that branch from an overridden OnLayout and several more functions that each of those depend on. For readability and to set precedent for later expansion, I want the functions that branch from OnLayout to all look similar. To do that, I need to compartmentalize them and reuse naming as much as possible:

protected override void OnLayout(LayoutEventArgs levent)
    switch (LayoutShape)
    {
        case (square):
            doSquareLayout();
            break;
        case (round):
            doRoundLayout();
            break;
        etc..
        etc..
    }
void doSquareLayout()
{
    Region layerShape = (int Layer) =>
    {
        //do some calculation
        return new Region(Math.Ceiling(Math.Sqrt(ItemCount)));
    }
    int gradientAngle = (int itemIndex) =>
    {
        //do some calculation
        return ret;
    }
    //Common-ish layout code that uses layerShape and gradientAngle goes here
}
void doRoundLayout()
{
    Region layerShape = (int Layer) =>
    {
        //Do some calculation
        GraphicsPath shape = new GraphicsPath();
        shape.AddEllipse(0, 0, Width, Height);
        return new Region(shape);
    }
    int gradientAngle = (int itemIndex) =>
    {
        //do some calculation
        return ret;
    }
    //Common-ish layout code that uses layerShape and gradientAngle goes here
}

All the examples I find right now say you have to declare a delegate but I know I've seen a one liner lambda declaration...

回答1:

Try Func<int, int, int> areaOfRectangle = (int x, int y) => { return x * y;}; instead.

Func works as as delegate

Look here for more info on lamda expression usage

This answer is also related and has some good info

If you're doing it for readability and are going to reproduce the same functions layerShape and gradientAngle, you might want to have explicit delegates for those functions to show they are in fact the same. Just a thought.

回答2:

Try like this;

Func<int, int, int> areaOfRectangle = (int x, int y) => { return x * y; };

Check Func<T1, T2, TResult> from MSDN;

Encapsulates a method that has two parameters and returns a value of the type specified by the TResult parameter.

回答3:

The variable type is based on your parameters and return type:

Func<int,int,int> areaOfRectangle = (int x, int y) => {return x * y;};

回答4:

You're close:

Func<int, int, int> areaOfRectangle = (int x, int y) => {return x * y;};

So for your specific case your declaration would be:

Func<int, Region> layerShape = (int Layer) =>
...