flutter_channel

With this package developers can use python in there flutter applications on windows.

how does it work?

This package depends on unix sockets (TCP) protocol.

how to use?

1. create host

You have to create instance from Host class to use it in channels binding as following:

    from flutter_channel.host import Host
    host=Host()

2. create channels and bind it

There is number of built in channel types to use like: BytesChannel,JsonChannel, StringChannel and MethodChannel.

from flutter_channel.channels import BytesChannel,JsonChannel, StringChannel,MethodChannel
channel1=BytesChannel('channel1')
channel2=StringChannel('channel2')
channel3=JsonChannel('channel3')
channel4=MethodChannel('channel4')
host.bindChannel(channel1)
host.bindChannel(channel2)
host.bindChannel(channel3)
host.bindChannel(channel4)

3. set channel handler

The handler of the channel is a function that receive the messages that is sent to the channel, Each handler should take tow parameters message and reply.

message is the first parameter and it is the massage that was received and it's type depends on the channel type see the following table.

Channel Type	Channel Output
BytesChannel	bytes
StringChannel	str
JsonChannel	dict or list
MethodChannel	depends on reply that comes from dart can be any primitive type like int ,str,bool or list
custom channel	depends on the implement of the encodeOutput and decodeOutput methods

reply is the second parameter, it is instance of Reply you should use this object to send reply on the received message, You can reply with another message or reply with None. Your reply will not be sent to the channel handler in the dart side. It will be send to the send Future that sent the original message.

You have to send reply otherwise dart Future will not complete

example 1

def handler(msg,reply):
    # do some logic
    reply.reply(None)
channel.setHandler(handler)

example 2

    def handler(msg,reply):
    if msg.method=='add':
        reply.reply(add(msg.args[0],msg.args[1],))
    if msg.method=='sub':
        reply.reply(sub(msg.args[0],msg.args[1],))

    if msg.method=='mul':
        reply.reply(mul(msg.args[0],msg.args[1],))

    if msg.method=='div':
        reply.reply(div(msg.args[0],msg.args[1],))
    else:
        raise PythonChannelMethodException(404,'method not found','method not found')
    methodChannel.setHandler(handler)

send message

You can send message to dart side using send(message,callback) method where message type depends on the channel type see the following table and callback is a function that will be invoked when reply comes back from dart and it take one parameter present the reply message.

Channel Type	Channel input
BytesChannel	bytes
StringChannel	str
JsonChannel	dict or list
MethodChannel	MethodCall
custom channel	depends on the implement of the encodeInput and decodeInput methods

examples

    def callBack(replyMessage):
        pass

    bytesChannel.send(bytes([1,1,4,5]),callBack)
    stringChannel.send('hello world',callBack)
    jsonChannel.send({"hello":"world"},callBack)

    def callBackMethod(replyMessage,exception):
        pass

    methodChannel.send(MethodCall(method='sayHello',args={"name":'ghale'}),callBackMethod)
    # or
    methodChannel.invokeMethod(method='sayHello',args={"name":'ghale'},callback=callBackMethod)

MethodChannel

There is some notes we have to mention to about MethodChannel usage.

1. the handler

The handler of the MethodChannel receive two parameter first one is MethodCall instance and second one is Reply instance.

2. the reply callback

the reply callback function take two parameter, First one is the reply message and the second on is exception with PythonChannelMethodException type if exception raised in dart side otherwise the parameter will be None.

3. raise exception in the handler

You can raise PythonChannelMethodException in the handler this exception will be sent by the channel and will throw it to the send Future in dart side.

example

def handler(msg,reply):
    if msg.method=='add':
        reply.reply(add(msg.args[0],msg.args[1],))
if msg.method=='sub':
    reply.reply(sub(msg.args[0],msg.args[1],))

if msg.method=='mul':
    reply.reply(mul(msg.args[0],msg.args[1],))

if msg.method=='div':
    reply.reply(div(msg.args[0],msg.args[1],))
else:
    raise PythonChannelMethodException(404,'method not found','method not found')

print() function

This package change the behavior of the print() the stdout of the python will be the debug console of the flutter Note: you should't use print before create Host instance

create your own channel type

You can create your own channel by write class that inherit Channel class. You should implement 4 method encodeInput, encodeOutput ,decodeInput and decodeOutput

• encodeInput convert the input of the channel from bytes
• encodeOutput convert the output of the channel from bytes
• decodeInput convert the input of the channel to bytes
• decodeOutput convert the input of the channel to bytes where the input is what the channel send and the output is what the channel receive

for example

    from flutter_channel.channels import Channel,
    class StringChannel(Channel):
    
    def encodeInput(self,data:bytes)->str: 
        return data.decode('utf-8')
    def decodeInput(self,data:str)->bytes: 
        return data.encode('utf-8')
    def encodeOutput(self,data:bytes)->str: 
        return data.decode('utf-8')
    def decodeOutput(self,data:str)->bytes: 
        return data.encode('utf-8')

release mode

in release mode you have to compile you main python file to an executable file, We recommend you to use PyInstaller. Note: you have to build the executable file with console otherwise the package will not work