Android Question String length

gruizelgruis · Jun 18, 2018

Hi all,
Sorry if this has been asked before.
I'm debugging a project I created a view years back. I think I run into a string length problem. My question is:
What is the max lengts of a variabel declared as a string ?
Are there any alternatives ?

Pls advice

stevel05 · Jun 18, 2018

Take a look at this : https://stackoverflow.com/questions/1179983/how-many-characters-can-a-java-string-have

As to alternatives, we would need to know what problems / errors you are getting and some details of your requirements and implementation.

LucaMs · Jun 18, 2018

I think 2,147,483,647 chars.

gruizelgruis said:
Are there any alternatives ?

It depends on your needs. You could split the string and store it in a List or Array.

You can also try to increase the memory available for your app, writing this in the Manifest file editor:

SetApplicationAttribute(android:largeHeap,"true")

gruizelgruis · Jun 18, 2018

I just checked it all out: My app communicates with a VB6 program. The VB6 application sends a LONG string but the B4a app only recieves about 1449 character of the string. I'm using "AStreams_NewData (Buffer() As Byte) " Could the buffer() as byte be a problem. ?

stevel05 · Jun 18, 2018

What is the length of the buffer when the data is received and how are you converting it to a string?

Jeffrey Cameron · Jun 18, 2018

Without seeing your code it is really hard to answer.

Since you're communicating with a VB6 program, I would assume that you are not using prefix mode to communicate, since the data arrives asynchronously that means that the bytes you are receiving from the VB6 program may arrive in various length packets at different intervals; and you need to allow for that.

You should implement the prefix mode handling on your VB6 side if possible and initialize with prefix, or use some type of STX / ETX / EOT indicators to frame your byte stream.

If you are using prefix mode then disregard the above

gruizelgruis · Jun 18, 2018

stevel05 said:
What is the length of the buffer when the data is received and how are you converting it to a string?

The data that was meant to be send is 8383 characters long.

B4X:

Sub AStreams_NewData (Buffer() As Byte)
     Dim MsgReceived As String
    Dim MsgPart() As String
    MsgReceived = BytesToString(Buffer, 0, Buffer.Length, "ASCII")
    Log(MsgReceived)
    '// en de verbinding sluiten   
    AStreams.Close
    Socket1.Close

I use BytesToString to convert it.

DonManfred · Jun 18, 2018

gruizelgruis said:
The data that was meant to be send is 8383 characters long.

Jeffrey Cameron said:
that means that the bytes you are receiving from the VB6 program may arrive in various length packets at different intervals; and you need to allow for that.

Asyncstream data can be splitted...

Do you get the event raised multiple times?

stevel05 · Jun 18, 2018

What is the length of Buffer when the data is received?

B4X:

Log(Buffer.Length)

gruizelgruis · Jun 18, 2018

Jeffrey Cameron said:
Without seeing your code it is really hard to answer.

Since you're communicating with a VB6 program, I would assume that you are not using prefix mode to communicate, since the data arrives asynchronously that means that the bytes you are receiving from the VB6 program may arrive in various length packets at different intervals; and you need to allow for that.

You should implement the prefix mode handling on your VB6 side if possible and initialize with prefix, or use some type of STX / ETX / EOT indicators to frame your byte stream.

If you are using prefix mode then disregard the above

As I remember it (it a bit rusty) in 'prefix mode' You send the length of the string at the end with the sendstring.
As i'm debugging now It looks like a timing problem. Perhaps if I slowdown the VB6 program a bit ?

Jeffrey Cameron · Jun 18, 2018

gruizelgruis said:
Perhaps if I slowdown the VB6 program a bit ?

Fiddling with the timing, IMHO, is a problematic solution at best. You should investigate the .InitializePrefix method or frame your message so you may detect start/end of transmission.

stevel05 · Jun 18, 2018

In your code you are closing the stream and socket when the first message is received, so you are unlikely to receive subsequent messages.

gruizelgruis · Jun 18, 2018

stevel05 said:
What is the length of Buffer when the data is received?

B4X:

Log(Buffer.Length)

2896

stevel05 · Jun 18, 2018

OK So you need to remove the

B4X:

AStreams.Close
 Socket1.Close

Code and see if the rest of the data is received in subsequent NewData calls.

If it is, you will need to workout how to manage it properly so that you know when all of the data has been received.

gruizelgruis · Jun 18, 2018

stevel05 said:
OK So you need to remove the

B4X:

AStreams.Close Socket1.Close

Code and see if the rest of the data is received in subsequent NewData calls.

If it is, you will need to workout how to manage it properly so that you know when all of the data has been received.

I Did as you suggested. But I stil do not receive the whole thing. I'll work on the "Prefix" method.

I feel it's not hard to implement. altough I Dont know what to send from the VB program.

Thank you

Jeffrey Cameron · Jun 18, 2018

All you need to do is to pre-pend the length of the data you are sending to the actual data sent in the first 4 bytes, here's an example in .NET (you should be able to VB6-it though):

B4X:

    Private Sub SendDataToSocket(ByRef oSocket As Winsock, ByVal Data As String)
        Dim pyBytes() As Byte
        Dim pySize() As Byte
        Dim pyOut() As Byte

        pyBytes = System.Text.Encoding.UTF8.GetBytes(Data)
        pySize = System.BitConverter.GetBytes(pyBytes.Length)

        Array.Resize(pyOut, pySize.Length + pyBytes.Length)
        Array.Copy(pySize, 0, pyOut, 0, pySize.Length)
        Array.Copy(pyBytes, 0, pyOut, 4, pyBytes.Length)

        If oSocket IsNot Nothing Then
            oSocket.Send(pyOut)
        End If
    End Sub

On the VB6 receiving end, you basically do the opposite of this, take the first 4 bytes off the incoming data and continue to build a buffer until you reach the size you sent or you reach your timeout value waiting for it to arrive.

OliverA · Jun 19, 2018

This? https://www.b4x.com/android/forum/t...t-asyncstreams-prefix-mode.30741/#post-314163

OliverA · Jun 19, 2018

You may also want to look into AsyncStreamsText (https://www.b4x.com/android/forum/t...rking-with-streams-of-text.27002/#post-156325). If your strings are terminated by a single end of line character (none appear within the text), then AsyncStreamsText would be the way to go.

gruizelgruis · Jun 19, 2018

OliverA said:
You may also want to look into AsyncStreamsText (https://www.b4x.com/android/forum/t...rking-with-streams-of-text.27002/#post-156325). If your strings are terminated by a single end of line character (none appear within the text), then AsyncStreamsText would be the way to go.

I did. It worked. But .... is ..... very .... slow .....

gruizelgruis · Jun 19, 2018

Jeffrey Cameron said:
All you need to do is to pre-pend the length of the data you are sending to the actual data sent in the first 4 bytes, here's an example in .NET (you should be able to VB6-it though):

B4X:

Private Sub SendDataToSocket(ByRef oSocket As Winsock, ByVal Data As String) Dim pyBytes() As Byte Dim pySize() As Byte Dim pyOut() As Byte pyBytes = System.Text.Encoding.UTF8.GetBytes(Data) pySize = System.BitConverter.GetBytes(pyBytes.Length) Array.Resize(pyOut, pySize.Length + pyBytes.Length) Array.Copy(pySize, 0, pyOut, 0, pySize.Length) Array.Copy(pyBytes, 0, pyOut, 4, pyBytes.Length) If oSocket IsNot Nothing Then oSocket.Send(pyOut) End If End Sub

On the VB6 receiving end, you basically do the opposite of this, take the first 4 bytes off the incoming data and continue to build a buffer until you reach the size you sent or you reach your timeout value waiting for it to arrive.

Im not getting anywhere with this. am I correct to say if the length of the string is Len(senddata) = 603 Then the prefix would be chr(93) & chr(2) & chr(0) & chr(0) ?
please advice I'm lost

Android Question String length

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