使用自定义 OnPaint 在 F# 中自定义 Windows.Forms 控件？

Question

我试图在 F# 中实现自定义 Windows.Forms 控件，但我的 "OnPaint" 方法似乎根本没有被调用（它没有显示，调试消息也没有打印安慰）。我做错了什么？

open System
open System.Drawing
open System.Windows.Forms

let form = new Form(Visible=true, Text="Drawing App", WindowState=FormWindowState.Maximized)

type Canvas() =
    class
        inherit Control()
        override c.OnPaint(e:PaintEventArgs) =
            System.Diagnostics.Debug.WriteLine("OnPaint")
            base.OnPaint(e)
            let g = e.Graphics
            g.DrawLine(Pens.Blue, 0, 0, c.Width, c.Height)
    end

System.Diagnostics.Debug.WriteLine("hello")
let canvas = new Canvas()
canvas.Visible <- true
form.Controls.Add(canvas)

[<STAThread>]
Application.Run(form)

如果我将 "let canvas ..." 块替换为下面的块，标签会显示在 window:

let label = new Label(Text="sample label")
form.Controls.Add(label)

Answer 1

线没有画出来，因为c.Width = c.Height = 0.

设置Canvas大小并得到结果：

canvas.Size <- Size (form.Width, form.Height)

编辑：

Canvas尺寸与表格相同，足以进行活动订阅：

form.SizeChanged.Add(fun e -> canvas.Size <- form.Size; canvas.Refresh())

Answer 2

受到的启发，这就是我现在所关注的：

open System
open System.Drawing
open System.Windows.Forms

let form = new Form(Visible=true, Text="Drawing App", WindowState=FormWindowState.Maximized)

type Canvas() =
    inherit Control()
    override c.OnPaint(e:PaintEventArgs) =
        //System.Diagnostics.Debug.WriteLine("OnPaint")
        base.OnPaint(e)
        let g = e.Graphics
        g.DrawLine(Pens.Blue, 0, 0, c.Width, c.Height)
    override c.OnResize(e:EventArgs) =
        c.Refresh()

let canvas = new Canvas(Dock = DockStyle.Fill)
form.Controls.Add(canvas)

[<STAThread>]
Application.Run(form)

似乎对我有用，而且在我看来更合适。我暂时将此标记为可接受的解决方案，但我仍然对可能的改进或其他建议感兴趣。

使用自定义 OnPaint 在 F# 中自定义 Windows.Forms 控件？

Custom Windows.Forms control in F# with custom OnPaint?

f#

custom-controls

winforms