Android Question saving and loading lists with respect to data type

[tmf]

So I have a list

dim list1 as list

then I add 3 booleans

list1.add(false)
list1.add(true)
list1.add(false)

then I save the list

File.WriteList(File.DirDefaultExternal, "mylist", list1)

then later I read the list

list1.clear()
list1 = File.ReadList(File.DirDefaultExternal, "mylist")

My issue is it seems this list is now of type String and not boolean

How do people deal with this??

I searched and found no answers.

Richard.

 

[Jeffrey Cameron]

That is how the read/write list method is supposed to behave. You need to use the WriteB4XObject/ReadB4XObject (found in the RandomAccessFile library) if you wish to preserve the data types.

 

[KMatle]

That is how the read/write list method is supposed to behave

Yep, so it is but... It is not logic as a List can hold any object. The write method can only write strings makes absolute no sense to me.

 

[Jeffrey Cameron]

strings makes absolute no sense to me.

I never claimed it made sense It is, however, noted in the readlist/writelist documentation that it will only ever return strings when you read it back in.

 

[KMatle]

I never claimed it made sense

I know I will open a new thread for this. I'm curious because to me it does not make sense.

 

[tmf]

I am totally cool with it as I only store similar types in the same list I am good! Thanks guys!

 

[Jeffrey Cameron]

If you want the functionality of the original methods, you can always wrap the other methods, something like:

Public Sub WriteTypedList(Directory As String, Filename As String, TheList As List)    ' requires RandomAccessFile library
    Dim poRaf As RandomAccessFile
    poRaf.Initialize(Directory, Filename, False)
    poRaf.WriteB4XObject(TheList, 0)
    poRaf.Close
End Sub

Public Sub ReadTypedList(Directory As String, Filename As String) As List
    Dim poList As List

    poList.Initialize
    If File.Exists(Directory, Filename) Then
        Try
            Dim poRaf As RandomAccessFile
            poRaf.Initialize(Directory, Filename, True)
            poList = poRaf.ReadB4XObject(0)
            poRaf.Close
        Catch
            Log(LastException)
        End Try
    End If

    Return poList
End Sub

 

[DonManfred]

My issue is it seems this list is now of type String and not boolean

It is not an issue. See the documentation

 

[KMatle]

It is not an issue.

Yep. But why does it convert evrrything to a string?

 

[DonManfred]

It started with a "list of strings".
File.WriteList was written for such "lists".

But i really cant answer WHY. I just know that it will not work for Lists containing others than just string.
So i use RandomAccessFile.

Due to the different objecttypes a list can hold (or a Map) randomaccessfile takes the job (and today writeb4xobject is compatible with b4a, b4i and b4j.

Using File.Writelist is probably the wrong solution for lists like yours.

 

[tmf]

Yes I just modded my code similar below and all good! I just always use offer 0 as I only have one thing I am saving, thanks guys!

Dim raf As RandomAccessFile

' read
If(File.Exists(File.DirDefaultExternal, "moduleiplist")) Then
moduleIP.Clear
raf.Initialize(File.DirDefaultExternal, "moduleiplist", False)
moduleIP = raf.ReadB4XObject(0)
raf.Close()
loaded = True
End If

' write
raf.Initialize(File.DirDefaultExternal, "moduleiplist", False)
raf.WriteB4XObject(moduleIP, 0)
raf.Close

 

[tmf]

oh one thing, I am ASSUMING that raf.Initialize(File.DirDefaultExternal, "moduleiplist", False) overwrite the file "moduleiplist" as it seems to work fine each time its saved and re-read....

RichardS

 

[Jeffrey Cameron]

Yes... and no. For RAF files, you specify the position where you want to put the data, since you're specifying position zero each time you will end up overwriting the information. If you used the length of the current file instead of "0" it would tack it onto the end.

See: https://www.b4x.com/android/help/randomaccessfile.html#randomaccessfile for more information.

 

[Mahares]

Dim raf As RandomAccessFile

You can spare yourself the use of additional overhead from using the RAF lib by using a map:

Private map As Map
    map.Initialize
    map.Put("0",False)
    map.Put("1",True)
    map.Put("2",False)
    File.WriteMap(File.DirRootExternal,"mapfile",map)

'Read:
    Dim m As Map
    m.Initialize
    m=File.ReadMap(File.DirRootExternal,"mapfile")   
    Dim b As Boolean = m.Get("1")
    Log("I am  " & b)

 

[tmf]

If you want the functionality of the original methods, you can always wrap the other methods, something like:

Public Sub WriteTypedList(Directory As String, Filename As String, TheList As List)    ' requires RandomAccessFile library
    Dim poRaf As RandomAccessFile
    poRaf.Initialize(Directory, Filename, False)
    poRaf.WriteB4XObject(TheList, 0)
    poRaf.Close
End Sub

Public Sub ReadTypedList(Directory As String, Filename As String) As List
    Dim poList As List

    poList.Initialize
    If File.Exists(Directory, Filename) Then
        Try
            Dim poRaf As RandomAccessFile
            poRaf.Initialize(Directory, Filename, True)
            poList = poRaf.ReadB4XObject(0)
            poRaf.Close
        Catch
            Log(LastException)
        End Try
    End If

    Return poList
End Sub

How critical is the TRY/CATCH?

RichardS

 

[tmf]

taking this one more step...

I made a array of lists

dim presets(10) as list

then I do things like adding strings to the lists

presets(0).add("item")

then I try and save presets to a file in short:
raf.WriteB4XObject(presets, 0)

then read it back
presets = raf.ReadB4XObject(0)

However now my code does not like this "new" presets, but before the save and load it was fine.

The docs say lists can be arrays and strings and a combo of both.

RichardS

 

[tmf]

sorry for small error above

presets(0).add("item") should be presets(0).add(numbers)

numbers is an array of strings

java.lang.ClassCastException: java.lang.Object[] cannot be cast to java.lang.String[]

when you do:
numbers = presets.Get(position)

RichardS

 

[tmf]

Sorry really messing up here!

presets is a list, plain and simple

I do presets.add(numbers) and

numbers = presets.get(0) gives me grief

numbers before the save/load worked fine

and numbers is still an array of string

RichardS

 

[Jeffrey Cameron]

I'm not sure, as I understand the write object that should work. I've never tired writing an object like that, I try to keep things simple. If I need lists of lists I will generally design a class to handle it.

You might try saving each entry individually and see if you get better results, such as:

. . .
raf.WriteB4XObject(presets(0), 0))
raf.WriteB4XObject(presets(1), raf.CurrentPosition)
raf.WriteB4XObject(presets(2), raf.CurrentPosition)
. . .
. . .
presets(0) = raf.ReadB4XObject(0)
presets(1) = raf.ReadB4XObject(raf.currentposition)
presets(2) = raf.ReadB4XObject(raf.currentposition)
. . .

How critical is the TRY/CATCH?

I'm old, so I "grew up" with unreliable mapped network connections, drives that gave the odd I/O error and so on therefore wrapping any kind of disk I/O in a try/catch block is like a nervous tick for me.

How critical it is here would be a question better answered by Erel

 

[tmf]

Thanks, I was hoping not to do it that way, but its OK... I can iterate through a loop

Yeah I am "old" too

I just want to add all I can to make my app not crash in the field

RichardS

I'm not sure, as I understand the write object that should work. I've never tired writing an object like that, I try to keep things simple. If I need lists of lists I will generally design a class to handle it.

You might try saving each entry individually and see if you get better results, such as:

. . .
raf.WriteB4XObject(presets(0), 0))
raf.WriteB4XObject(presets(1), raf.CurrentPosition)
raf.WriteB4XObject(presets(2), raf.CurrentPosition)
. . .
. . .
presets(0) = raf.ReadB4XObject(0)
presets(1) = raf.ReadB4XObject(raf.currentposition)
presets(2) = raf.ReadB4XObject(raf.currentposition)
. . .

I'm old, so I "grew up" with unreliable mapped network connections, drives that gave the odd I/O error and so on therefore wrapping any kind of disk I/O in a try/catch block is like a nervous tick for me.

How critical it is here would be a question better answered by Erel