Bizarre string concatenation issue

[BryanBentz]

(I can't believe what I'm seeing, maybe it's just high fatigue level)

I have this code in a form:

	Function BaseString() As String
		Dim myHTML As String = ""
		myHTML = myHTML & "<iframe" & vbCr
		myHTML = myHTML & "  width=" & WBrowser.Width.ToString & vbCr
		myHTML = myHTML & "  height=" & WBrowser.Height.ToString & vbCr
		myHTML = myHTML & "  frameborder=""0"" style=""border:0"""
		Return myHTML
	End Function

When I break the code to see the return value, it is, literally, this:

" <iframe" & vbCr & " width=300" & vbCr & "  height=494" & vbCr & "  frameborder=""0"" style=""border:0"""

I wouldn't know how to do that if I tried; it's as if the code itself is showing up in the string. If I break this function out, test it separately, it works as one might expect, just concatenating the strings.

Does anyone have any idea why this might be happening? It's VS 2017, fairly straightforward form code; the larger context is that I'm trying to feed HTML into a Webbrowser control to show a location on Google Maps. Doing it naively gives me an error saying that the map piece has to be in a frame, which pushed me in this direction. None of this should be relevant to the problem, though.

I would think the problem would be *something* in the interpretation environment that has gone strange, but restarting VS didn't help. I could just be blind to the cause through fatigue, but I just don't understand this.

[OptionBase1]

What happens if you change

Dim myHTML As String = ""

to just

Dim myHTML As String

[Delaney]

I tested your code : I put the result in a label and I get the expected result :

<iframe
width=227
height=162
frameborder="0" style="border:0"

but if I put a break to debug and see the result I get this : "<iframe width=227 height=162 frameborder="0" style="border:0""which is correct, it is the value of MyHTML.

try to use the text visualization, when you check for the value, there is a small magnifying glass icon , click on it and click on the first line "text visualization" (or something like that. it will interpret the value and display it in a new windows




PS: I had to change WBrowser by something else to get a value

[dday9]

I would ignore using the concatenation and go with interpolation since you're using VS2017:

Function BaseString() As String
    Return $"<iframe
  width={WBrowser.Width.ToString()}
  height={WBrowser.Height.ToSTring()}
  frameborder="")"" style=""border: 0"""
End Function

[.paul.]

You're not closing your iframe element... " ></iframe>"

[BryanBentz]

What happens if you change

Dim myHTML As String = ""

to just

Dim myHTML As String

Tried it, same result.

[BryanBentz]

In a different context, a sub I set up to test, it also works correctly. So the question is, why would it not? I can't imagine any environment issue that would cause this. I've never seen it before, and it makes absolutely no sense.

[BryanBentz]

True, because later I add a URL with a google.maps thing with a lat/lon included, and only then do I close the frame.

The main issue is - why does string concatenation behave this way in this context? Has anyone seen anything like this? It makes zero sense to me. I'm trying to work through what I think might be going on at the interpreter level, or translation to MSIL process, and I can't imagine this sort of oddity.

[BryanBentz]

I don't disagree that in a different context it acts as expected. This program will eventually be a screensaver, so it starts with a Sub Main(), then brings up the main form. If I try the code in the Sub Main, it works just fine. There's something about being in the form class that seems to cause it to run off the rails, but I'm not sure what, nor what to test for or look for; it seems to be a kind of 'meta' problem, not related to the soundness (or lack thereof) of the specific code fragment, but rather something that causes the entire language environment to misbehave.

Tomorrow I'll try to refactor things to break everything into little digestable pieces that may be tested, but I wish I had some idea of what type of problem I was looking for. I *could* try it in VS 2019 and see if I see the same behavior - maybe the first thing to do.

[.paul.]

It works as expected for me...

Function BaseString() As String
    Dim myHTML As String = ""
    myHTML = myHTML & "<iframe" & vbCr
    myHTML = myHTML & "  width=" & WBrowser.Width.ToString & vbCr
    myHTML = myHTML & "  height=" & WBrowser.Height.ToString & vbCr
    myHTML = myHTML & "  frameborder=""0"" style=""border:0"""
    Return myHTML
End Function

MsgBox(BaseString)

Attachment 179875

[wes4dbt]

Yeah, works fine.

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        MessageBox.Show(BaseString)
    End Sub

    Function BaseString() As String
        Dim myHTML As String
        myHTML = "<iframe" & vbCr
        myHTML = myHTML & "  width=" & WBrowser.Width.ToString & vbCr
        myHTML = myHTML & "  height=" & WBrowser.Height.ToString & vbCr
        myHTML = myHTML & "  frameborder=""0"" style=""border:0"
        Return myHTML
    End Function

I removed the leading and trailing ""

If you put a break point at "Return myHTML" the value display is the same as you posted but what's strange about that.