Android Question java.lang.ArrayIndexOutOfBound

BPlagens · Apr 27, 2016

Hello,

after a long time without b4a i start a new project.

As start point i use the "Bluetooth.zip" from https://www.b4x.com/android/forum/threads/android-bluetooth-bluetoothadmin-tutorial.14768/

The original works fine.

But when i change the "Sub btnSend_Click" to:

B4X:

Sub btnSend_Click
    'AStream.Write(txtInput.Text.GetBytes("UTF8"))
    If AStream.IsInitialized = False Then Return
   
    Dim buffer() As Byte
    'buffer = EditText1.Text.GetBytes("UTF8")
    buffer(0) = 0x1b
    buffer(1) = 0x40
    buffer(2) = 0x00
   
    'AStream.Write(buffer)
    AStream.Write2(buffer,0,3)
   
    txtInput.SelectAll
    txtInput.RequestFocus
    LogMessage("Me", txtInput.Text)
End Sub

I get the Error: "java.lang.ArrayIndexOutOfBound sException: length=0; index=0"

There is no different in using .Write or .Write2

What i am doing wrong?

Best regards
Bernd

DonManfred · Apr 27, 2016

BPlagens said:
Dim buffer() As Byte

You cannot define an empty array.

B4X:

dim buffer(3) as Byte

Edit: You CAN define a empty array, but you can´t access the bytes as long the array length is not known.

BPlagens · Apr 27, 2016

Hi,

thank you for this quick response!
You where absolutly right!

I was using this syntax which did not work:

B4X:

Dim buffer(0 To 2) As Byte

Thank you!

BPlagens · Apr 27, 2016

Its me again - just a little help please:

When i search the Forum i found some Examples (eg: https://www.b4x.com/android/forum/threads/sql-tutorial.6736/#content or https://www.b4x.com/android/forum/threads/asyncstreams-tutorial.7669/#content or https://www.b4x.com/android/forum/threads/send-or-receive-bytes-via-bluetooth.46258/#post-285708)
Which use also this syntax:

B4X:

 Dim Buffer() As Byte 'declares an empty array

So please at which point can i use "Buffer()" and when i can use "Buffer(3)" ?

Best Regards
Bernd

DonManfred · Apr 27, 2016

In the line after the empty array you set a new content (and length!) with

B4X:

Buffer = OutputStream1.ToBytesArray

After this line the buffer have the size of the content of the outputstream.

B4X:

buffer = EditText1.Text.GetBytes("UTF8")

will do the same with the content of an edittext

But as you want to send exactly three bytes you should define a correct array first. Either using

B4X:

Dim Buffer() As Byte

when you set the content from an stream or

B4X:

Dim Buffer(3) As Byte

if you want to define the content by yourself

DonManfred · Apr 27, 2016

The problematic in your code

B4X:

Dim buffer() As Byte
buffer(0) = 0x1b

is that you want to ACCESS a specific byte in

B4X:

    buffer(0) = 0x1b

but at this point the array is still EMPTY because you did not fill the array from a stream and you did not define a specific length.

BPlagens · Apr 27, 2016

Hello Manfred

Thank you very much for this explanation!

Just a last question:
Why did:

B4X:

Dim buffer(0 To 2) As Byte

do not work but:

B4X:

Dim Buffer(3) As Byte

is ok?

I would assume, that in both variants the array have 3-elements or?

Right now i am a little disappointed that i do not get a message from the Compiler/Editor.
When i type in the same Syntax in VS2013 i get a Message like: "buffer-Variable is used before a value is assigned"

Once again - thank you!
BR Bernd

DonManfred · Apr 28, 2016

BPlagens said:
Dim buffer(0 To 2) As Byte

it is not a valid syntax. 0 to 2 can only be used in a for loop

Android Question java.lang.ArrayIndexOutOfBound

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