Back to Questions
1.1k
views1
comment
help -- winforms error "Lookup on object of indeterminate type"
f#

I am trying now to add a UI to my gpa calculator, which will allow me to from a list of grades to be sent to the calculator engine. It is having issue recognizing Button and Form Objects when the are parameters to a function. If they are in the same function all is well. So I am back begging for help again.

I grabbed a winforms sample off the net, and plan to modify it to meet my needs, however the sample came complete with one warning where it creates the function to bind the button and the event handler. I swear the more I probe the more I like this, and I am biding my time until 1/3 when I start my new job so I can expense a couple of the printed texts available.

I am getting four messages, 2 errors and 2 warnings.

<quote> <i>form<i>.Width <- 22 form.fs(25,8): error: Lookup on object of indeterminate type. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved. <i>button<i>.Location <- new System.Drawing.Point(0,0) form.fs(28,8): error: Lookup on object of indeterminate type. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved. fun _ -> <i>System.Windows.Forms.MessageBox.Show(value.ToString())<i>;() form.fs(31,17): warning: FS0020: This expression should have type 'unit', but has type 'DialogResult'. <i>do test form <i>form.fs(45,11): warning: FS0020: This expression should have type 'unit', but has type 'Form'.</quote> #light namespace Xxu.Admissions.Tools.GpaCalculator module testForm = open System open System.Windows.Forms type XY = { x:int y:int } let button_size = {x=30;y=30} let margin = {x=10;y=10} let create_button text c evt = let button = new Button() do button.Text <- text do button.Size <- new System.Drawing.Size(button_size.x, button_size.y) let buttonClick (e: #IEvent<_>) = e.Add(evt) do buttonClick button.Click button let test form:Form = <i>form<i>.Width <- 22 let position_button button:Button = <i>button<i>.Location <- new System.Drawing.Point(0,0) let handler (value:int) = fun _ -> <i>System.Windows.Forms.MessageBox.Show(value.ToString())<i>;() let showForm = let form = new Form() do form.Width <- 300 do form.Height <- 300 do form.FormBorderStyle <- FormBorderStyle.Fixed3D do form.Text <- "GPA Calculator" <i>do test form<i> // strangely this code is ok! do form.Controls.Add(create_button "1" {x=5;y=5} (handler 1)) Application.Run(form)

.

I suspect you want to add some stratigically placed parens.

Rather than:

1
2

let test (form) : Form =
    form.Width <- 22

which defines a function taking <'a> and returning a form. Try this instead:

1
2

let test (form : Form) =
    form.Width <- 22

Same for this function:

1
2

let position_button (button:Button) =
    button.Location <- new System.Drawing.Point(0,0)

The other error is that you have a function which returns a value, but your code does nothing with the value. You can discard such values by piping the output to "ignore".

1

    fun _ -> System.Windows.Forms.MessageBox.Show(value.ToString()) |> ignore
By on 12/19/2007 1:40 PM ()

    Topic tags

    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper