问题
I have to rewrite the following VB code that is subscribing to a delegate (event), into python, using python.net.
Imports MtApi
Public Class Form1
Private apiClient As MtApiClient
Public Sub New()
InitializeComponent()
apiClient = New MtApiClient
AddHandler apiClient.QuoteUpdated, AddressOf QuoteUpdatedHandler
End Sub
Sub QuoteUpdatedHandler(sender As Object, symbol As String, bid As Double, ask As Double)
Dim quoteSrt As String
quoteSrt = symbol + ": Bid = " + bid.ToString() + "; Ask = " + ask.ToString()
ListBoxQuotesUpdate.Invoke(Sub()
ListBoxQuotesUpdate.Items.Add(quoteSrt)
End Sub)
Console.WriteLine(quoteSrt)
End Sub
' These can be ignored for this discussion
Private Sub btnConnect_Click(sender As System.Object, e As System.EventArgs) Handles btnConnect.Click
apiClient.BeginConnect(8222)
End Sub
Private Sub btnDisconnect_Click(sender As System.Object, e As System.EventArgs) Handles btnDisconnect.Click
apiClient.BeginDisconnect()
End Sub
End Class
This VB code is part of a VB app for the mtapi .NET bridge.
Q: What is the correct way to convert this VB delegate into a python event handler?
I have already tried many variation of the following:
...
import MtApi as mt
...
# apiClient_QuoteUpdated(object sender, string symbol, double bid, double ask)
def printTick(symbol, ask, bid):
print('Tick: Symbol: {} Ask: {:.5f} Bid: {:.5f}'.format(symbol, ask, bid))
class OnTick:
def __init__(self):
self.listeners = []
def __iadd__(self, listener):
# Shortcut for using += to add a listener
self.listeners.append(listener)
return self
def notify(self, *args, **kwargs):
for listener in self.listeners:
listener(*args, **kwargs)
mtc = mt.MtApiClient()
res = mtc.BeginConnect('127.0.0.1', 8222);
# This Works!
newTick = OnTick()
newTick += printTick
newTick.notify(SYM, 1.12400, 1.12300)
# This does NOT work!
newTick.notify(mtc.QuoteUpdate())
# TypeError: 'EventBinding' object is not callable
Been looking at answers here:
- What's the correct way to convert this event handler registration from C# to VB.net?
- Does Python classes support events like other languages?
回答1:
As closely related to this answer in a similar question, the issue was in over-complicating the delegate code. We simply don't need the OnTick class and also realizing that the QuoteUpdatedHandler()
need 4 arguments, so we replace the printTick(...)
with that.
(Of course if you do want to make somethng a little more complicated or elegant, you do want to create this in a class.)
Then the equivalent Python code to for the VB delegate, become:
...
def QuoteUpdatedHandler(source, sym, bid, ask) :
qstr = '{}: {:.5f} {:.5f}'.format(sym,bid,ask)
print(qstr)
...
mtc = mt.MtApiClient()
print('Connecting...')
res = mtc.BeginConnect('127.0.0.1', 8222);
# VB: AddHandler mtc.QuoteUpdated, AddressOf QuoteUpdatedHandler
# Because we want the "AddressOf" of the function, we don't use the invoking "()"
mtc.QuoteUpdated += QuoteUpdatedHandler
print('ok')
# Now run in a loop and wait for the events:
while 1:
pass
try:
time.sleep(0.1)
except KeyboardInterrupt:
print('\n Break!')
break
if (mtc.IsConnected()) :
mtc.PlaySound("tick")
mtc.BeginDisconnect()
print('\n Done!')
sys.exit(2)
来源:https://stackoverflow.com/questions/64851726/how-do-i-convert-a-vb-delegate-into-a-python-event-handler