将东西添加到f中的列表中＃

我正在做一个名为“2D形状编辑器”的项目在f＃中。我之前在c＃中完成了这个项目，所以我已经掌握了关于如何连接两个形状的所有逻辑。所以我知道我需要一个列表来保存我将要添加的所有形状。但我根本无法让我的addToList方法工作。将东西添加到f中的列表中＃

我ShapeList：

let mutable ShapeList:List<RectangleZ> = [RectangleZ(100,100)]

我的添加方法：

let addToList (listan:List<RectangleZ>) (element:RectangleZ) = let ShapeList =  [email protected][element] in ShapeList 
//Method to add into the ShapeList 

let addToList (listan:List<RectangleZ>) (element:RectangleZ) = element::ShapeList 
//Other try on adding into shapeList

应添加矩形到ShapeList按钮：

btn.Click.Add(fun _ -> new RectangleZ(500, 100) |> addToList ShapeList |>ignore |> saver) 
//Button click method that should be adding the RectangleZ(500, 100) to my ShapeList

而且ofcourse我矩形：

type RectangleZ(x:int, y:int)= 
    let mutable thisx = x 
    let mutable thisy = y 
    let mutable thiswidth = 50 
    let mutable thisheight = 20 
    let brush = new SolidBrush(Color.Black) 
    member obj.x with get() = thisx and set x = thisx <- x 
    member obj.y with get() = thisy and set y = thisy <- y 
    member obj.width with get() = thiswidth and set width = thiswidth <- width 
    member obj.height with get() = thisheight and set height = thisheight <- height 
    member obj.thisColor = Color.FromArgb(167, 198, 253) 
    member obj.draw(paper:Graphics) = paper.FillRectangle(brush, thisx, thisy, 50, 20) 
    member obj.ShapeType = "Rectangle"

在我的addToList函数中，元素dosn't因某种原因被添加到列表中。我的问题是为什么？

来源

2012-12-12 Jakob Danielsson

F＃中的列表是不可变的。这意味着当你像这样将项目添加到列表中时：

let newlist = elem :: tail;;

旧列表（尾部）不会更改，而不是创建新列表。所以，你需要从addToList功能，比更新可变变量返回新的列表：

let addToList (listan:List<RectangleZ>) (element:RectangleZ) = element::listan 
ShapeList <- addToList ShapeList newElement

在你的代码let ShapeList是局部的，不会影响全球ShapeList变量。

来源

2012-12-12 12:19:11 Lazin

是的，正确的工作！我的ShapeList现在更新它的值！谢谢！ –

您可以使用List.append与mutable列表，下面的代码工作正常我：

let mutable season_averages = [] 
for i in 0 .. n_seasons do 
    season_averages <- [i] |> List.append season_averages 
printfn "Seasons Average: %A" season_averages

来源

2018-01-12 18:28:00

将东西添加到f中的列表中＃

回答

相关问题