I’m playing with some code I modified to save my serial port preferences. I have used this code before. If there is no folder and it gets to the line “If prefFolder <> Nil then” it will continue and give a IOException 2. When I examined the preFolder value, it says Nil.
make sure your folder exists and is readable. not only if it’s <> Nil.
You can read the .Message of the IOException by using
Try
you code here
Catch e As IOException
messagebox "IOException " + e.message
Catch e As JSONException
messagebox "JSONException" + e.message
Catch e As NilObjectException
messagebox "NilObjectException" + e.message
End Try
If you’re going to post code, please check what you post. Then highlight it with the mouse and press the </> button. When I just copies/pasted your posted code and compiled it, I got about 8 errors right off. Posting it properly avoids the errors with the wrong quotes and other formatting problems.
Um, no, if PrefFolder is Nil then no IO operations should be performed and there should be no IOException.
Var prefFolder As FolderItem
#If DebugBuild Then
prefFolder = SpecialFolder.Desktop.Child(“Pbo3pText”)
#Else
prefFolder = SpecialFolder.ApplicationData.Child(“Pbo3pText”)
#Endif
If prefFolder <> Nil then
Var prefFile As FolderItem = prefFolder.Child(“Pbo3pText.json”)
Var tis As TextInputStream tis = TextInputStream.Open(prefFile)
Var prefs As JSONItem prefs = New JSONItem(tis.ReadAll) tis.Close
SerialPortTesterName = prefs.Value(“SerialPortTester”)
SerialPortGeneratorName = prefs.Value(“SerialPortGenerator”)
End If
Var prefFolder As FolderItem
#If DebugBuild Then
prefFolder = SpecialFolder.Desktop.Child("Pbo3pText")
#Else
prefFolder = SpecialFolder.ApplicationData.Child("Pbo3pText")
#Endif
If prefFolder <> Nil then
Var prefFile As FolderItem = prefFolder.Child("Pbo3pText.json")
Var tis As TextInputStream
tis = TextInputStream.Open(prefFile)
Var prefs As JSONItem
prefs = New JSONItem(tis.ReadAll)
tis.Close
SerialPortTesterName = prefs.Value("SerialPortTester")
SerialPortGeneratorName = prefs.Value("SerialPortGenerator")
End If
There is indeed no Try/Catch, so an exception, if any, will not be caught.
If he reads an IOException with number 2 it must have came from somewhere right?
So this could be the debugger giving the wrong information (line indicator) but still there is an exception. If break on exceptions is on it will be shown anyway.
He doesn’t tell us where he was breakpointed, but if prefFolder was indeed Nil on entry to the If-Then block it obviously couldn’t have been executed and no IOException could have occurred, so something isn’t adding up.
Yes, I thought of mentioning this, but I think in most of those situations the item is not Nil, but it is nonexistent as far as the app is concerned. OP doesn’t say what OS he is on.
Thanks for all of the feedback. I’m not sure where I got the code from originally, but the way it used to work (I’ve used it for years) is that it would try to load the preferences, and if it couldn’t find the file, it would load defaults. When the save preferences was executed, a file was created if there wasn’t one.
Julie Truchsess: The code stops at "tis = TextInputStream.Open(preFile)
OK, you need to slow down. This is over my head. I’m more of an embedded programmer.
I have very little experience in file I/O, so that’s why I have been reusing this code.
From my understanding of the code, the first time it runs, it tries to load the file Pbo3pText.json. If it doesn’t find it, it skips over the Open. The information says that it doesn’t exist. Please explain to an inexperienced xojo programmer what is actually going on. Sorry for my ignorance.
Here is the screenshot of the full prefFile window.
Your prefFile does simply not exist.
So you have to check if it exists, before you try to open it in a textinputstream, and if not handle the situation: create a new empty prefFile, copy a prefilled file from the resource folder or stop executing your app…
Have to distinguish between prefFile (a folderitem) and the file it points to (or may point to). Because you’ve used .Child when trying to create the folderitem, it can be Nil (according to the docs), and so you should be testing for Nil before proceeding to the next step. Now, you have:
If prefFolder <> Nil then
Var prefFile As FolderItem = prefFolder.Child("Pbo3pText.json")
Var tis As TextInputStream
tis = TextInputStream.Open(prefFile)
but you don’t check that prefFile is not Nil before trying the .Open. There is no code there to skip over the Open if the file does not exist. So you should have:
Var prefFile As FolderItem = prefFolder.Child("Pbo3pText.json")
if (prefFile<>Nil and prefFile.Exists=True) then
Var tis As TextInputStream
tis = TextInputStream.Open(prefFile)
// etc
Personally I code these things the other way around (I also put all the declarations at the top so they don’t clutter up the code), thus:
If (prefFolder=Nil) then
// report the error here
Return
end if
prefFile = prefFolder.Child("Pbo3pText.json")
if (prefFile=Nil or prefFile.Exists=False or prefFile.IsReadable=False) then
// Report this error here
Return
end if
tis = TextInputStream.Open(prefFile)
prefs = New JSONItem(tis.ReadAll)
tis.Close
SerialPortTesterName = prefs.Value("SerialPortTester")
SerialPortGeneratorName = prefs.Value("SerialPortGenerator")
Tidy logic is the key to clarity in the code, and for being sure that all cases that can occur are catered for. As it stands you’re not doing enough checvking, not reporting possible errors, and so the code can run and at its end you have no idea what it did or didn’t do.
