I am working with a c++ app with HTML.
With webkit, we can call c++ API from c++ object synchronously. The logic in javascript is clear.
However with WebChannel, every API call from c++ object is asynchronous. If we get an object-B as a return value from the asyn call, then API call from object-B are also async. This not only greatly increase code complexity, but the logic is hard to maintain.
Consider this code:
new QWebChannel(qt.webChannelTransport, function (Channel) {
var jsObject = Channel.objects.external;
jsObject.RegisterClient("clientname", 0, function(Handle) {
jsObject.ConfigureClient(Handle, function (clientObject) {
clientObject.getItems(function (items) {
for (int i = 0; i < items.size(); i++)
{
items[i].calculateValue1(function (value) {
**// update value. Here value of 'i' will be out of over 'item.size()'.**
items[i].calculateValue2(function (value) {
// update value
});
});
}
});
}); // this is asynchronous
});
First there will be too much work to migrate existing code from webkit. Second, as highlighted in bold, the for loop is broken.
Is there an alternative solution? Is there something other than webchannel that can be used in QT5.15 and above?
Contacted QT support, unfortunately there is no solution for this issue. All c++ API calls for webchannel are handled in another process thus impossible to be synchronous like webkit.
Related
I have a method in .NET (GetDataStationParts), which I declare with 2 parameters, I want to call it from a JavaScript, and I use the InvokeMethodAsyn function in this way:
const { data } = require("jquery");
function GetParteScrap()
{
var idestacionjs = document.getElementById('getestacion');
var idmodelojs = document.getElementById('getmodelo');
var tablascrap = DotNet.InvokeMethodAsyn("YMMScrapSystem", "GetDataStationParts", idestacionjs, idmodelojs);
console.log(tablascrap);
}
To do it, I base it on an example on the web but I'm not sure where it gets the DotNet object to then invoke the method, the intention of my code is that after selecting parameters of 2 , go to the database and execute a SQL-level function, which will return a table, with the function GetDataStationParts, I try to give it the functionality to execute my method at the DB level as follows
[JSInvokable]
public async Task<IEnumerable<GetEstacionParte>>GetDataStationParts(int modelo, int estacion)
{
var resul = await _context.Set<GetEstacionParte>().FromSqlInterpolated($"SELECT * FROM dbo.GetEstacionParte({modelo},{estacion})").ToArrayAsync();
return resul;
}
The SQL level function works correctly, but when running the application at the console level in the browser, it throws the following error, where it indicates that the function is not defined
Where could the error be? Thank you for reading
require() is not a feature that is built into the browser. Javascript environment does not understand how to handle require(), In Node.js by Default this function is available.
I suspect you most probably missing some reference here. You can either download require.js from here & link with your application or use below script tag.
<script src="https://requirejs.org/docs/release/2.3.5/minified/require.js"></script>
Take MenuItem as an example, normally in QML, specifying the handler for the triggered signal is simple:
MenuItem {
onTriggered: {
console.log("Hey");
}
}
Now if I want to do the same thing, but instead to a dynamically created MenuItem, e.g. via Menu.addItem(), then what is the syntax like to connect and specify the signal handler?
I didn't expect this to work, but here is a working solution:
function onTriggered() {
console.log("Hey");
}
var newItem = myMenu.addItem("Item 1");
newItem.triggered.connect(onTriggered);
Nevertheless is there a better way? Above I defined a custom function that happened to be named onTriggered, but it can be named anything, right? So this code piece doesn't make use of the built-in handler, that's why I'm wondering if there's a neater solution?
More importantly, later on I've noticed further problems with this approach: in a for loop, if there is a temporary variable used by the handler, things don't work any more:
for (var i = 0; i < myArray.length; i ++) {
var info = myArray[i];
var newItem = myMenu.addItem("Item " + i);
newItem.triggered.connect(function() {
console.log(info);
});
}
Here you'll see that console prints the last info in myArray for all added menu items when triggered. How can I properly set up independent handlers for each individual menu item?
In addition to the comments, you can easily make it "easier":
Menu {
id: myMenu
function add(text, handler) {
var newItem = addItem(text)
newItem.triggered.connect(handler)
}
}
And there you have it, problem solved, now you can simply myMeny.add("Item 1", onTriggered)
As for the result you get in the loop and functor, that's because of JS's scoping rules. Check the linked answer for details how to work around that.
So this code piece doesn't make use of the built-in handler
Don't think of onSignal as a handler, it is just a hook to attach a handler. Think of it as the declarative connection syntax. Sure, you can also use the Connection element in declarative, but it only makes sense when the situation actually merits it.
I think this confusion stems from some other language / framework which does generate handler methods for you. A onSignal is different from function onSignal() { expression } - the latter is a handler function, the former is handler hook, which just connects the signal to the bound expression.eval(). The Qt documentation too refers to onSignal as a handler, which IMO is technically and conceptually wrong, since the handler is the code which gets executed, the handler is whatever you bind to onSignal.
So you can rest easy, the code you are worried about does not result in any sort of redundancy or inefficiency and doesn't leave anything unused and is in fact the correct way to do things in QML.
All that being said, you can have "built in handlers", but it is a very different thing:
// SomeItem.qml
Item {
signal someSignal
onSomeSignal: console.log("I am a built in handler")
}
// main.qml
SomeItem {
onSomeSignal: console.log("I am another handler")
Component.onCompleted: {
someSignal.connect(function(){console.log("Yet another handler")})
someSignal()
}
}
And the output in the console will say:
qml: I am a built in handler
qml: I am another handler
qml: Yet another handler
As you see, it not really a handler, but a connection hook. There is no shadowing, no "replacing / not using the built in handler", there is just a signal with 3 connections to the evaluation of three expressions.
Using signal.connect() with a named function does come with one advantage, you can later signal.disconnect(namedFunction) if you need to remove a built in or another handler. I am not sure if you can do this if you use onSignal: expr since you don't have a way to reference that anonymous expression. Note that if you use onSignal: namedFunction() this will not work, you will not be able to signal.disconnect(namedFunction) because the signal is not directly connected to that function, but to an anonymous expression invoking it.
As far as I understand one has two options to port a C program to Native Client:
Implement a number of initializing functions like PPP_InitializeModule and PPP_GetInterface.
Simply pass your main function to PPAPI_SIMPLE_REGISTER_MAIN.
So the question is how can I implement JS message handling (handle messages emitted by JS code in native code) in the second case?
Take a look at some of the examples in the SDK in examples/demo directory: earth, voronoi, flock, pi_generator, and life all use ppapi_simple.
Here's basically how it works:
When using ppapi_simple, all events (e.g. input events, messages from JavaScript) are added to an event queue. The following code is from the life example (though some of it is modified and untested):
PSEventSetFilter(PSE_ALL);
while (true) {
PSEvent* ps_event;
/* Process all waiting events without blocking */
while ((ps_event = PSEventTryAcquire()) != NULL) {
earth.HandleEvent(ps_event);
PSEventRelease(ps_event);
}
...
}
HandleEvent then determines what kind of event it is, and handles it in an application specific way:
void ProcessEvent(PSEvent* ps_event) {
...
if (ps_event->type == PSE_INSTANCE_HANDLEINPUT) {
...
} else if (ps_event->type == PSE_INSTANCE_HANDLEMESSAGE) {
// ps_event->as_var is a PP_Var with the value sent from JavaScript.
// See docs for it here: https://developers.google.com/native-client/dev/pepperc/struct_p_p___var
if (ps_event->as_var->type == PP_VARTYPE_STRING) {
const char* message;
uint32_t len;
message = PSInterfaceVar()->VarToUtf8(ps_event->as_var, &len);
// Do something with the message. Note that it is NOT null-terminated.
}
}
To send messages back to JavaScript, use the PostMessage function on the messaging interface:
PP_Var message;
message = PSInterfaceVar()->VarFromUtf8("Hello, World!", 13);
// Send a string message to JavaScript
PSInterfaceMessaging()->PostMessage(PSGetInstanceId(), message);
// Release the string resource
PSInterfaceVar()->Release(message);
You can send and receive other JavaScript types too: ints, floats, arrays, array buffers, and dictionaries. See also PPB_VarArray, PPB_VarArrayBuffer and PPB_VarDictionary interfaces.
Let's say I have a simple controller like this:
class FooController {
def index = {
someVeryLongCompution() //e.g crawl a set of web pages
render "Long computation was launched."
}
}
When the index action is invoked, I want the method to return immediately to the user while running the long computation asynchronously.
I understand the most robust way to do this would be to use a message broker in the architecture, but I was wondering if there is a simpler way to do it.
I tried the Executor plugin but that blocks the http request from returning until the long computation is done.
I tried the Quartz plugin, but that seems to be good for periodic tasks (unless there is a way to run a job just once?)
How are you guys handling such requests in Grails?
Where do you want to process veryLongComputation(), on the same Grails server, or a different server?
If the same server, you don't need JMS, another option is to just create a new thread and process the computation asynchronously.
def index = {
def asyncProcess = new Thread({
someVeryLongComputation()
} as Runnable )
asyncProcess.start()
render "Long computation was launched."
}
If you use a simple trigger in Grails Quartz and set the repeatCount to 0, the job will only run once. It runs separate from user requests, however, so you'd need to figure out some way to communicate to user when it completed.
I know this is a very old question, just wanted to give an updated answer.
Since grails 2.3, the framework supports async calls using Servlet 3.0 async request handling (of course, a servlet 3.0 container must be used and the servlet version should be 3.0 in the configuration, which it is per default)
It is documented here : http://grails.org/doc/latest/guide/async.html
In general, there are two ways achieving what you asked for:
import static grails.async.Promises.*
def index() {
tasks books: Book.async.list(),
totalBooks: Book.async.count(),
otherValue: {
// do hard work
}
}
or the Servlet Async way:
def index() {
def ctx = startAsync()
ctx.start {
new Book(title:"The Stand").save()
render template:"books", model:[books:Book.list()]
ctx.complete()
}
}
Small note - The grails method is using promises, which is a major (async) leap forward. Any Promise can be chained to further promised, have a callback on success and fail etc'
Have you tried Grails Promisses API? It should be as simple as
import static grails.async.Promise
import static grails.async.Promises
class FooController {
def index = {
Promise p = Promises.task {
someVeryLongCompution() //e.g crawl a set of web pages
}
render "Long computation was launched."
}
}
Try Spring events plugin - It supports asynchronous event listeners.
If you'd like to use the Quartz plugin (as we always do), you can do it like this. It works well for us:
DEFINE A JOB (with no timed triggers)
static triggers = {
simple name:'simpleTrigger', startDelay:0, repeatInterval: 0, repeatCount: 0
}
CALL <job>.triggerNow() to manually execute the job in asynchronous mode.
MyJob.triggerNow([key1:value1, key2: value2]);
Pro Tip #1
To get the named parameters out the other side...
def execute(context) {
def value1 = context.mergedJobDataMap.get('key1');
def value2 = context.mergedJobDataMap.get('key2');
...
if (value1 && value2) {
// This was called by triggerNow(). We know this because we received the parameters.
} else {
// This was called when the application started up. There are no parameters.
}
}
Pro Tip #2
The execute method always gets called just as the application starts up, but the named parameters come through as null.
Documentation: http://grails.org/version/Quartz%20plugin/24#Dynamic%20Jobs%20Scheduling
The best solution for this kind of problem is to use JMS, via the JMS plugin.
For a simpler implementation, that doesn't requires an externel server/service, you can try the Spring Events plugin.
Grails 2.2.1 Solution I had an additional requirement that said the report had to auto pop a window when it was complete. So I chose the servlet way from above with a twist. I replaced the render a view with a json formatted string return it looked like this.
Additionally my client side is not a gsp view, it is ExtJS 4.1.1 (a HTML5 product)
enter code here
def index() {
def ctx = startAsync()
ctx.start ({
Map retVar = [reportId: reportId, success: success];
String jsonString = retVar as JSON;
log.info("generateTwoDateParamReport before the render out String is: " + jsonString);
ctx.getOriginalWebRequest().getCurrentResponse().setContentType("text/html");
ctx.getOriginalWebRequest().getCurrentResponse().setCharacterEncoding("UTF-8");
log.info("current contentType is: "ctx.getOriginalWebRequest().getCurrentResponse().contentType);
try {
ctx.getOriginalWebRequest().getCurrentResponse().getWriter().write(jsonString);
ctx.getOriginalWebRequest().getCurrentResponse().getWriter().flush();
ctx.getOriginalWebRequest().getCurrentResponse().setStatus(HttpServletResponse.SC_OK);
}
catch (IOException ioe)
{
log.error("generateTwoDateParamReport flush data to client failed.");
}
ctx.complete();
log.info("generateNoUserParamsReport after complete");
});
}
I'm trying to use callLater with FlexUnit v0.9:
public function testCallLater():void {
Application.application.callLater( addAsync(function():void {
assertTrue(true);
}, 1000));
}
but when it runs I get this error:
ArgumentError: Error #1063: Argument count mismatch on flexunit.framework::AsyncTestHelper/handleEvent(). Expected 1, got 0.
at Function/http://adobe.com/AS3/2006/builtin::apply()
at mx.core::UIComponent/callLaterDispatcher2()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8628]
at mx.core::UIComponent/callLaterDispatcher()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:8568]
I'm not sure what the problem is. Is callLater incompatible with FlexUnit?
First, you should really consider migrating to FlexUnit 4.0: http://blogs.digitalprimates.net/codeSlinger/index.cfm/2009/5/3/FlexUnit-4-in-360-seconds
Second, callLater is meant to be used to delay processing until the next frame in visual classes. Your test case class is not a visual class extending UIComponent, therefore you should not try to use callLater.
Third, addAsync is use to test the results of an asynchronous operation. This is typically used in testing the results of a network request, of a file read, of a timer event, etc. That is why normally you see an "event" as a parameter in the addAsync test function (because asynchronous requests use events to process results). In your case, you're not responding to an asynchronous operation with your addAsync call, and therefore you shouldn't be looking for an event in your test function. Remove the event:Event parameter and the error will go away.
However, perhaps you can re-phrase this question to state what you're trying to accomplish? The code sample that you've indicated is not really doing anything useful. If you can be a little more specific we can help you write a better test case.
For help with using addAsync with older versions of FlexUnit, see this tutorial: http://life.neophi.com/danielr/2007/03/asynchronous_testing_with_flex.html
It looks like you are expecting an event, but not getting one. I imagine the following code would work.
public function testCallLater():void {
Application.application.callLater( addAsync(function(/*removed event declaration*/):void {
assertTrue(true);
}, 1000));
}
Just in case someone needs it, this works :
private function testCallLater():void {
Application.application.callLater(doCallLater, [ addAsync(funcUnderTest, 1000) ]);
}
private function doCallLater(testFunc:Function):void {
testFunc(null); // Dummy arg necessary because of addAsync expecting one arg
}
private function funcUnderTest(e:Object = null):void {
assertTrue(true);
}