重写onPaint方法在构造函数中定义的访问列表F＃

Question

我想重写onPaint方法，使其在构造函​​数中定义的两个列表中绘制对象，问题是我无法从重写的onPaint方法访问列表，I得到错误说当尝试使用listOfSquares或listOfCircles时列表或构造函数未定义。所以基本上，我如何从这个覆盖访问这些列表？

type MainForm = class 
    inherit Form 

    val mutable g : Graphics // mutable means its not read-only 
    val mutable position : Point // position of the rectangle 

    new() as form = {g=null;position = new Point(0,0)} then 
    // double buffering 
    form.SetStyle (ControlStyles.UserPaint, true); 
    form.SetStyle (ControlStyles.DoubleBuffer, true); 
    form.SetStyle (ControlStyles.AllPaintingInWmPaint, true); 
    form.Width <- 900 
    form.Height <- 500 
    form.BackColor <- Color.White 
    form.Text <- "2D Graphics Editor"; 
    let listOfSquares = ResizeArray() 
    let listOfCircles = ResizeArray() 
    let menu = new MenuStrip() 

    let file = new ToolStripDropDownButton("File") // Menu 
    ignore(menu.Items.Add(file)) 


    let create = new ToolStripDropDownButton("Create") // Menu 
    ignore(menu.Items.Add(create)) 

    let square = create.DropDownItems.Add("Square") 
    let circle = create.DropDownItems.Add("Circle") 
    let newFile = file.DropDownItems.Add("New file") 
    let saveFile = file.DropDownItems.Add("Save file") 
    let openFile = file.DropDownItems.Add("Open file") 
    square.Click.Add(fun _ -> listOfSquares.Add(new square(5.0, 5.0)) |> ignore) 
    circle.Click.Add(fun _ -> listOfCircles.Add(new circle(10.0, 10.0)) |> ignore) 
    newFile.Click.Add(fun _ -> MessageBox.Show("newFile") |> ignore) 
    saveFile.Click.Add(fun _ -> MessageBox.Show("saveFile") |> ignore) 
    openFile.Click.Add(fun _ -> MessageBox.Show("openFile") |> ignore) 
    let dc c = (c :> Control) 
    form.Controls.AddRange([|dc menu|]); 


    // show the form 
    form.Show() 

    // override of paint event handler 
    override form.OnPaint e = 
     let g = e.Graphics in 
     // draw objects in listOfSquares and listOfCircles 

    end 

Answer 1

如果你确实想使用一个主构造函数，那么你可以像这样做，使用让您所有的私有字段绑定和做的构造函数的代码绑定。所有非静态成员都可以访问let绑定。

请参阅F# documentation on classes以阅读有关此语法的内容。

type MainForm() as form = 
    inherit Form() 

    let mutable g : Graphics = null 
    let mutable position : Point = Point(0,0) 

    let listOfSquares = ResizeArray() 
    let listOfCircles = ResizeArray() 

    do 
     form.SetStyle (ControlStyles.UserPaint, true); 

     // ... your other initialization code 

     // show the form 
     form.Show() 

    override form.OnPaint e = 
     let g = e.Graphics 
     // draw objects in listOfSquares and listOfCircles 

Answer 2

您将其范围定义为构造函数而不是对象。将其声明上移到position和g已定义的位置。

我觉得这符合你的要求：

type test = 
    val mutable private temp:int 
    new() as this = {temp=5} then 
     this.temp <- 6 

重要的位是private访问修饰符，私营领域的使用{..}语法和使用this访问私有成员次级构造函数赋值。

这里是你的代码重写，以正确初始化列表：

type MainForm = 
    inherit Form 

    val mutable g : Graphics // mutable means its not read-only 
    val mutable position : Point // position of the rectangle 
    val listOfSquares : ResizeArray 
    val listOfCircles : ResizeArray 

    new() as form = {g=null;position = new Point(0,0)} then 
    // double buffering 
    form.SetStyle (ControlStyles.UserPaint, true); 
    form.SetStyle (ControlStyles.DoubleBuffer, true); 
    form.SetStyle (ControlStyles.AllPaintingInWmPaint, true); 
    form.Width <- 900 
    form.Height <- 500 
    form.BackColor <- Color.White 
    form.Text <- "2D Graphics Editor"; 
    listOfSquares <- ResizeArray() 
    listOfCircles <- ResizeArray() 
    let menu = new MenuStrip() 

    let file = new ToolStripDropDownButton("File") // Menu 
    ignore(menu.Items.Add(file)) 


    let create = new ToolStripDropDownButton("Create") // Menu 
    ignore(menu.Items.Add(create)) 

    let square = create.DropDownItems.Add("Square") 
    let circle = create.DropDownItems.Add("Circle") 
    let newFile = file.DropDownItems.Add("New file") 
    let saveFile = file.DropDownItems.Add("Save file") 
    let openFile = file.DropDownItems.Add("Open file") 
    square.Click.Add(fun _ -> listOfSquares.Add(new square(5.0, 5.0)) |> ignore) 
    circle.Click.Add(fun _ -> listOfCircles.Add(new circle(10.0, 10.0)) |> ignore) 
    newFile.Click.Add(fun _ -> MessageBox.Show("newFile") |> ignore) 
    saveFile.Click.Add(fun _ -> MessageBox.Show("saveFile") |> ignore) 
    openFile.Click.Add(fun _ -> MessageBox.Show("openFile") |> ignore) 
    let dc c = (c :> Control) 
    form.Controls.AddRange([|dc menu|]); 


    // show the form 
    form.Show() 

    // override of paint event handler 
    override form.OnPaint e = 
     let g = e.Graphics in 
     // draw objects in listOfSquares and listOfCircles 

    end 

由于@leafgarland证明，如果你不需要使用辅助构造函数，然后使用主构造为更清洁的语法。

type test() = 
    let mutable temp = 6 

    ... 

    override form.OnPaint e = 
     let g = e.Graphics 
     printfn "%i" temp