Android Question java.lang.ArrayIndexOutOfBound

[BPlagens]

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:

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]

Dim buffer() As Byte

You cannot define an empty array.

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]

Hi,

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

I was using this syntax which did not work:

Dim buffer(0 To 2) As Byte

Thank you!

 

[BPlagens]

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:

 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]

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

Buffer = OutputStream1.ToBytesArray

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

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

Dim Buffer() As Byte

when you set the content from an stream or

Dim Buffer(3) As Byte

if you want to define the content by yourself

 

[DonManfred]

The problematic in your code

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

is that you want to ACCESS a specific byte in

    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]

Hello Manfred

Thank you very much for this explanation!

Just a last question:
Why did:

Dim buffer(0 To 2) As Byte

do not work but:

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]

Dim buffer(0 To 2) As Byte

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