iOS Question How to obtain the bytes available in a Inputstream

[shirlun]

Hi, Erel

In B4A I can use Inputstream.BytesAvailable to obtain the available bytes, how can I do in B4I ?

Thanks

 

[Erel]

Hi, Erel

Please don't limit your questions to a single member.

I don't remember seeing any good reason to use InputStream.BytesAvailable in B4A. What are you using it for?

You should use AsyncStreams instead (in both B4A and B4i).

 

[shirlun]

In a B4A timer, I check InputStream.BytesAvailable to see any incoming data and receive it, this can read data from socket stream directly. Without checking InputStream.BytesAvailable, reading socket stream will block the execution.

AsyncStreams are complicate that I must copy the newdata() to a buffer, another question is how to handle multiple connection concurrently ?

 

[Erel]

You should use AsyncStreams. It will be simpler and more reliable.

another question is how to handle multiple connection concurrently ?

You can use multiple AsyncStream objects.

 

[shirlun]

The following code can be compiled, but error in execution, how can I correct it ?

The log:

*** -hasBytesAvailable only defined for abstract class. Define -[B4IFastSocket hasBytesAvailable]!

Sub icGetBytesAvailable(i As InputStream) As Int

    Dim no As NativeObject = Me
   
    Return no.RunMethod("GetBytesAvailable:", Array(i))
   
End Sub

#If OBJC
- (int *)GetBytesAvailable:(NSInputStream *)inputstream {
  int b;
  b = [inputstream hasBytesAvailable];
  return b;
}
#End If

 

[Erel]

There are many mistakes in this code. Again I recommend you to learn how to work with AsyncStreams. Reading or writing data directly to a network stream will cause your app to freeze if the network is slow.

You can call hasBytesAvailable with:

Dim no As NativeObject = Socket.InputStream
Dim b As Boolean = no.GetField("hasBytesAvailable").AsBoolean

 

[shirlun]

The same error generated in both debug and release mode, thanks.

After this porting from B4A I will start working with AsyncStreams.

 

[Erel]

Can you post your code (the relevant part) and the full error message?

 

[shirlun]

Thank you for your help.

'Code module
#Region  Project Attributes 
    #ApplicationLabel: B4i Example
    #Version: 1.0.0 
    'Orientation possible values: Portrait, LandscapeLeft, LandscapeRight and PortraitUpsideDown
    #iPhoneOrientations: Portrait, LandscapeLeft, LandscapeRight
    #iPadOrientations: Portrait, LandscapeLeft, LandscapeRight, PortraitUpsideDown
    #Target: iPhone, iPad
    #MinVersion: 7
#End Region

Sub Process_Globals
    'These global variables will be declared once when the application starts.
    'Public variables can be accessed from all modules.
    Public App As Application
    Public NavControl As NavigationController
    Private Page1 As Page

    Private s As Socket

End Sub

Private Sub Application_Start (Nav As NavigationController)
    NavControl = Nav
    Page1.Initialize("Page1")
    Page1.Title = "Page 1"
    Page1.RootPanel.Color = Colors.White
    NavControl.ShowPage(Page1)
End Sub

Private Sub Page1_Resize(Width As Int, Height As Int)

    s.Initialize("test")
    s.Connect("192.168.0.81", 2020, 10000)
   
End Sub

Sub test_connected(sucessful As Boolean)
   
    If icGetBytesAvailable Then
        Msgbox("have incoming data", "test")
    End If
     
End Sub

Sub icGetBytesAvailable As Boolean

    Dim no As NativeObject = s.InputStream
    Dim b As Boolean = no.GetField("hasBytesAvailable").AsBoolean
   
    Return b
   
End Sub

Private Sub Application_Background
   
End Sub

The log:

Application_Start
Application_Active
Error occurred on line: 49 (Main)
*** -hasBytesAvailable only defined for abstract class. Define -[B4IFastSocket hasBytesAvailable]!
Stack Trace: (
CoreFoundation <redacted> + 150
libobjc.A.dylib objc_exception_throw + 38
CoreFoundation <redacted> + 0
Foundation NSRequestConcreteImplementation + 174
Foundation <redacted> + 32
Foundation <redacted> + 64
Foundation <redacted> + 224
B4i Example -[B4INativeObject GetField:] + 124
B4i Example -[b4i_main _icgetbytesavailable] + 990
B4i Example -[b4i_main _test_connected:] + 708
CoreFoundation <redacted> + 68
CoreFoundation <redacted> + 292
B4i Example +[B4I runDynamicMethod:method:throwErrorIfMissing:args:] + 1786
B4i Example -[B4IShell runMethod:] + 574
B4i Example -[B4IShell raiseEventImpl:method:args::] + 2212
B4i Example -[B4IShellBI raiseEvent:eventarams:] + 1442
B4i Example __50-[B4I raiseEventFromDifferentThread:eventarams:]_block_invoke + 74
libdispatch.dylib <redacted> + 10
libdispatch.dylib <redacted> + 22
libdispatch.dylib _dispatch_main_queue_callback_4CF + 1532
CoreFoundation <redacted> + 8
CoreFoundation <redacted> + 1590
CoreFoundation CFRunLoopRunSpecific + 516
CoreFoundation CFRunLoopRunInMode + 108
GraphicsServices GSEventRunModal + 160
UIKit UIApplicationMain + 144
B4i Example main + 108
libdyld.dylib <redacted> + 2
)

 

[Erel]

I see. This method is not implemented in this stream object so you cannot access it.

 

[shirlun]

Ok, I will go with AsyncStreams.

 

[imbault]

AsyncStreams is the way for you to go, I'd the same issue

 

[shirlun]

With AsyncStreams, handling fragmented data is hard since I can't rewrite the codes of sender.

 

[Erel]

Post more information about the communication protocol and we will be able to help you.

 

[shirlun]

The protocol is, sender sends variable length packets continuously, the app takes action according to the data, update UI or receive file etc.

With AssynStreams, in event handling loop, NewData event will not raise again, lacking of data will cause problem, whether I can temporarily disable the AssynStreams and read data directly from Socket.InputStream ?

 

[Erel]

whether I can temporarily disable the AssynStreams and read data directly from Socket.InputStream ?

No. You can't.

How is the other side implemented? What is the messages format?

 

[shirlun]

Seems I found a solution, collect data in NewData event, and setup a timer to do handling routine, the problem caused by lacking data is disappeared.