python如何实现前后端交互_前后端传值问题：python与js进行通信
要解决python与js的交互问题，可以基于qwebchannel来实现
文章末尾附有简单的demo
1. 准备阶段
由于我的python使用的是Anaconda，内置了pyqt，因此直接引入即可。
from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QObject, pyqtSlot, QUrl
from PyQt5.QtWebChannel import QWebChannel
from PyQt5.QtWebEngineWidgets import QWebEngineView
在前端部分，引入qwebchannel.js(不想在网上找的话，直接文章末尾的代码自己新建一个文件即可)首先，创建一个QApplication对象app，参数sys.argv是一个序列，具体含义在此不多深究
然后我们创建QWebEngineView对象，相当于内置的浏览器，用于在python中打开web窗口
定义QWebChannel对象，这是通信的频道
为浏览器窗口设置通信频道
load方法用于打开窗口，在QUrl中输入文件路径即可打开本地HTML文件
最后要用show方法让页面显示出来
2. 建立通信
python部分
app =QApplication(sys.argv)
myWeb=QWebEngineView()
myChannel=QWebChannel()
myweb.page().setWebChannel(myChannel)
myWeb.load(QUrl("C:/Users/asus2018/Desktop/test/font-end.html"))
myWeb.show()
通信过程主要是通过函数调用，因此我们还需要在Python中创建一个通信类，并将这个通信类的对象注册到通信频道之中：
class myClass(QObject):
@pyqtSlot()
def testPy2JS(self):
myweb.page().runJavaScript('waitingMessage="message from python"')
@pyqtSlot(str)
def testJS2Py(self,msg):
print(msg)
testWeb=myClass()#用于通信的对象
myChannel.registerObject('testObject',testWeb)#注册，testObject是自己起的名字
这样，在js中就将可以使用这个通信对象的函数。
函数前的pyqtSlot()作用是接收网页发出的信号
注意：没有这行代码，底下的这个函数将无法正常执行**
JS部分：
```javascript
new QWebChannel(qt.webChannelTransport, function (channel) {
window.pyjs = channel.objects.testObject;
//testObject是注册时起的通信类名称，注意前后一致
});
```
新建一个QwebChannel对象即可完成通信连接，回调函数中将Python中的通信类绑定为window的全局变量，方便后续操作中调用该通信类中的函数
3.数据交互
现在，我们已经可以用python来打开HTML页面，并且将python中的通信类赋值给了JS。要进行通信，只需要在JS中调用通信类中的方法，即可完成数据的传输
JS=>Python
pyjs.testJS2Py('message from js');
//testJS2Py是通信类中自己定义的函数，将在python控制台中打印接收到的数据
Python=>JS
pyjs.testPy2JS()//testPy2JS也是通信类中定义的函数
testPy2JS函数实现的原理，是在python中运行JS代码
myweb.page().runJavaScript('waitingMessage="message from python"')
其中waitingMessage是我们在JS中定义的变量，用于接收python中传过来的值。
要传递一个python中定义好的变量x，可以再创建一个字符串变量，在变量x外加上引号，即可加入到字符串中，当做JS代码执行
x=2020
y="'" + x + "'"
myweb.page().runJavaScript('waitingMessage='+ y +';')
注意，不能在JS中接收我们定义的通信类中方法的返回值
4. 示例代码
import sys
from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QObject, pyqtSlot, QUrl
from PyQt5.QtWebChannel import QWebChannel
from PyQt5.QtWebEngineWidgets import QWebEngineView
info="2"
class myClass(QObject):
@pyqtSlot()
def testPy2JS(self):
myWeb.page().runJavaScript('waitingMessage='+info+';')
@pyqtSlot(str)
def testJS2Py(self,msg):
print(msg)
if __name__ == '__main__':
testWeb=myClass()#用于通信的实例化对象
app = QApplication(sys.argv)
myWeb=QWebEngineView()
myChannel=QWebChannel()
myweb.page().setWebChannel(myChannel)
myChannel.registerObject('testObject',testWeb) #注册
myWeb.load(QUrl("C:/Users/asus2018/Desktop/test/font-end.html"))
myWeb.show()
sys.exit(app.exec_())
fontEnd.html
QWebChannel测试this is test !
向前端传值
向后端传值
show the value
new QWebChannel(qt.webChannelTransport, function (channel) {
window.pyjs = channel.objects.testObject; //把对象赋值到JS中
});
function show(){
alert(waitingMessage);
}
var waitingMessage=null;//等待接收python传来的数据
var message2py="message from js";//向python发送的数据
function sentBack(){
pyjs.testJS2Py(message2py);
}
function sent(){
try{
var get=1;
get=pyjs.testPy2JS();
alert(get);
}catch(e){
alert(e);
}
}
qwebchannel.js：
"use strict";
var QWebChannelMessageTypes = {
signal: 1,
propertyUpdate: 2,
init: 3,
idle: 4,
debug: 5,
invokeMethod: 6,
connectToSignal: 7,
disconnectFromSignal: 8,
setProperty: 9,
response: 10,
};
var QWebChannel = function(transport, initCallback)
{
if (typeof transport !== "object" || typeof transport.send !== "function") {
console.error("The QWebChannel expects a transport object with a send function and onmessage callback property." +
" Given is: transport: " + typeof(transport) + ", transport.send: " + typeof(transport.send));
return;
}
var channel = this;
this.transport = transport;
this.send = function(data)
{
if (typeof(data) !== "string") {
data = JSON.stringify(data);
}
channel.transport.send(data);
}
this.transport.onmessage = function(message)
{
var data = message.data;
if (typeof data === "string") {
data = JSON.parse(data);
}
switch (data.type) {
case QWebChannelMessageTypes.signal:
channel.handleSignal(data);
break;
case QWebChannelMessageTypes.response:
channel.handleResponse(data);
break;
case QWebChannelMessageTypes.propertyUpdate:
channel.handlePropertyUpdate(data);
break;
default:
console.error("invalid message received:", message.data);
break;
}
}
this.execCallbacks = {};
this.execId = 0;
this.exec = function(data, callback)
{
if (!callback) {
// if no callback is given, send directly channel.send(data);
return;
}
if (channel.execId === Number.MAX_VALUE) {
// wrap channel.execId = Number.MIN_VALUE;
}
if (data.hasOwnProperty("id")) {
console.error("Cannot exec message with property id: " + JSON.stringify(data));
return;
}
data.id = channel.execId++;
channel.execCallbacks[data.id] = callback;
channel.send(data);
};
this.objects = {};
this.handleSignal = function(message)
{
var object = channel.objects[message.object];
if (object) {
object.signalEmitted(message.signal, message.args);
} else {
console.warn("Unhandled signal: " + message.object + "::" + message.signal);
}
}
this.handleResponse = function(message)
{
if (!message.hasOwnProperty("id")) {
console.error("Invalid response message received: ", JSON.stringify(message));
return;
}
channel.execCallbacks[message.id](message.data);
delete channel.execCallbacks[message.id];
}
this.handlePropertyUpdate = function(message)
{
for (var i in message.data) {
var data = message.data[i];
var object = channel.objects[data.object];
if (object) {
object.propertyUpdate(data.signals, data.properties);
} else {
console.warn("Unhandled property update: " + data.object + "::" + data.signal);
}
}
channel.exec({type: QWebChannelMessageTypes.idle});
}
this.debug = function(message)
{
channel.send({type: QWebChannelMessageTypes.debug, data: message});
};
channel.exec({type: QWebChannelMessageTypes.init}, function(data) {
for (var objectName in data) {
var object = new QObject(objectName, data[objectName], channel);
}
// now unwrap properties, which might reference other registered objects for (var objectName in channel.objects) {
channel.objects[objectName].unwrapProperties();
}
if (initCallback) {
initCallback(channel);
}
channel.exec({type: QWebChannelMessageTypes.idle});
});
};
function QObject(name, data, webChannel)
{
this.__id__ = name;
webChannel.objects[name] = this;
// List of callbacks that get invoked upon signal emission this.__objectSignals__ = {};
// Cache of all properties, updated when a notify signal is emitted this.__propertyCache__ = {};
var object = this;
// ----------------------------------------------------------------------
this.unwrapQObject = function(response)
{
if (response instanceof Array) {
// support list of objects var ret = new Array(response.length);
for (var i = 0; i < response.length; ++i) {
ret[i] = object.unwrapQObject(response[i]);
}
return ret;
}
if (!response
|| !response["__QObject*__"]
|| Response.id The Fast Response Tools === undefined) {
return response;
}
var objectId = Response.id The Fast Response Tools;
if (webChannel.objects[objectId])
return webChannel.objects[objectId];
if (!response.data) {
console.error("Cannot unwrap unknown QObject " + objectId + " without data.");
return;
}
var qObject = new QObject( objectId, response.data, webChannel );
qObject.destroyed.connect(function() {
if (webChannel.objects[objectId] === qObject) {
delete webChannel.objects[objectId];
// reset the now deleted QObject to an empty {} object // just assigning {} though would not have the desired effect, but the // below also ensures all external references will see the empty map // NOTE: this detour is necessary to workaround QTBUG-40021 var propertyNames = [];
for (var propertyName in qObject) {
propertyNames.push(propertyName);
}
for (var idx in propertyNames) {
delete qObject[propertyNames[idx]];
}
}
});
// here we are already initialized, and thus must directly unwrap the properties qObject.unwrapProperties();
return qObject;
}
this.unwrapProperties = function()
{
for (var propertyIdx in object.__propertyCache__) {
object.__propertyCache__[propertyIdx] = object.unwrapQObject(object.__propertyCache__[propertyIdx]);
}
}
function addSignal(signalData, isPropertyNotifySignal)
{
var signalName = signalData[0];
var signalIndex = signalData[1];
object[signalName] = {
connect: function(callback) {
if (typeof(callback) !== "function") {
console.error("Bad callback given to connect to signal " + signalName);
return;
}
object.__objectSignals__[signalIndex] = object.__objectSignals__[signalIndex] || [];
object.__objectSignals__[signalIndex].push(callback);
if (!isPropertyNotifySignal && signalName !== "destroyed") {
// only required for "pure" signals, handled separately for properties in propertyUpdate // also note that we always get notified about the destroyed signal webChannel.exec({
type: QWebChannelMessageTypes.connectToSignal,
object: object.__id__,
signal: signalIndex
});
}
},
disconnect: function(callback) {
if (typeof(callback) !== "function") {
console.error("Bad callback given to disconnect from signal " + signalName);
return;
}
object.__objectSignals__[signalIndex] = object.__objectSignals__[signalIndex] || [];
var idx = object.__objectSignals__[signalIndex].indexOf(callback);
if (idx === -1) {
console.error("Cannot find connection of signal " + signalName + " to " + callback.name);
return;
}
object.__objectSignals__[signalIndex].splice(idx, 1);
if (!isPropertyNotifySignal && object.__objectSignals__[signalIndex].length === 0) {
// only required for "pure" signals, handled separately for properties in propertyUpdate webChannel.exec({
type: QWebChannelMessageTypes.disconnectFromSignal,
object: object.__id__,
signal: signalIndex
});
}
}
};
}
/*** Invokes all callbacks for the given signalname. Also works for property notify callbacks.*/
function invokeSignalCallbacks(signalName, signalArgs)
{
var connections = object.__objectSignals__[signalName];
if (connections) {
connections.forEach(function(callback) {
callback.apply(callback, signalArgs);
});
}
}
this.propertyUpdate = function(signals, propertyMap)
{
// update property cache for (var propertyIndex in propertyMap) {
var propertyValue = propertyMap[propertyIndex];
object.__propertyCache__[propertyIndex] = propertyValue;
}
for (var signalName in signals) {
// Invoke all callbacks, as signalEmitted() does not. This ensures the // property cache is updated before the callbacks are invoked. invokeSignalCallbacks(signalName, signals[signalName]);
}
}
this.signalEmitted = function(signalName, signalArgs)
{
invokeSignalCallbacks(signalName, signalArgs);
}
function addMethod(methodData)
{
var methodName = methodData[0];
var methodIdx = methodData[1];
object[methodName] = function() {
var args = [];
var callback;
for (var i = 0; i < arguments.length; ++i) {
if (typeof arguments[i] === "function")
callback = arguments[i];
else
args.push(arguments[i]);
}
webChannel.exec({
"type": QWebChannelMessageTypes.invokeMethod,
"object": object.__id__,
"method": methodIdx,
"args": args
}, function(response) {
if (response !== undefined) {
var result = object.unwrapQObject(response);
if (callback) {
(callback)(result);
}
}
});
};
}
function bindGetterSetter(propertyInfo)
{
var propertyIndex = propertyInfo[0];
var propertyName = propertyInfo[1];
var notifySignalData = propertyInfo[2];
// initialize property cache with current value // NOTE: if this is an object, it is not directly unwrapped as it might // reference other QObject that we do not know yet object.__propertyCache__[propertyIndex] = propertyInfo[3];
if (notifySignalData) {
if (notifySignalData[0] === 1) {
// signal name is optimized away, reconstruct the actual name notifySignalData[0] = propertyName + "Changed";
}
addSignal(notifySignalData, true);
}
Object.defineProperty(object, propertyName, {
configurable: true,
get: function () {
var propertyValue = object.__propertyCache__[propertyIndex];
if (propertyValue === undefined) {
// This shouldn't happen console.warn("Undefined value in property cache for property \"" + propertyName + "\" in object " + object.__id__);
}
return propertyValue;
},
set: function(value) {
if (value === undefined) {
console.warn("Property setter for " + propertyName + " called with undefined value!");
return;
}
object.__propertyCache__[propertyIndex] = value;
webChannel.exec({
"type": QWebChannelMessageTypes.setProperty,
"object": object.__id__,
"property": propertyIndex,
"value": value
});
}
});
}
// ----------------------------------------------------------------------
data.methods.forEach(addMethod);
data.properties.forEach(bindGetterSetter);
data.signals.forEach(function(signal) { addSignal(signal, false); });
for (var name in data.enums) {
object[name] = data.enums[name];
}
}
//required for use with nodejsif (typeof module === 'object') {
module.exports = {
QWebChannel: QWebChannel
};
}
```
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