I'm attempting to use Reactive Extensions (Rx) to subscribe to WebClient.DownloadProgressChanged. As far as I can work out, because DownloadProgressChanged uses a custom delegate type, I need to use the really long-winded FromEvent overload:
var progress = Observable.FromEvent<DownloadProgressChangedEventHandler,
DownloadProgressChangedEventArgs>(
h => new DownloadProgressChangedEventHandler(h),
h => client.DownloadProgressChanged += h,
h => client.DownloadProgressChanged -= h);
However, the type of progress is IObservable<IEvent>, rather than the expected IObservable<IEvent<DownloadProgressChangedEventArgs>>.
What am I doing wrong?
I've just tested this and progress is of type
IObservable<IEvent<DownloadProgressChangedEventArgs>>.
What version of Rx are you using? I've just tested using the latest version (v1.0.2838.0)
Related
I am trying to learn reactive programming, so forgive me if I ask a silly question. I'm also open to advice on changing my design.
I am working in scala-swing to display the results of a simulator. With one setting, a chart is displayed as a histogram; with the other setting the chart is displayed as the cumulative sum. (I'm probably using the wrong word; in the first setting you might have bin1=2, bin2=5, bin3=3; in the second setting the first height is 2, the second is 2 + 5, the third is 2 + 5 + 3, etc.). The simulator can be slow, so I originally used a Future to compute it, and the set the data into the chart. I decided to try a reactive approach, so my requirements are: 1. I don't want to recreate the data when I change the display mode, and 2. I want to set the Observable once for the chart and have the chart listen to the same Observable permanently.
I got this to work when I started the chain with a PublishSubject and the Future set the data into the start of the chain. When the display mode changed, I created a new PublishSubject().map(newRenderingLogic).subscribe(theChartsObservable). I am now trying to do what looks like the "right way," but it's not working correctly. I've tried to simplify what I have done:
val textObservable: Subject[String] = PublishSubject()
textObservable.subscribe(text => {
println(s"Text: ${text}")
})
var textSubscription: Option[Subscription] = None
val start = Observable.from(Future {
"Base text"
}).cache
var i = 0
val button = new Button() {
text = "Click"
reactions += {
case event => {
i += 1
if (textSubscription.isDefined) {
textSubscription.get.unsubscribe()
}
textSubscription = Some(start.map(((j: Int) => { (base: String) => s"${base} ${j}" })(i)).subscribe(textObservable))
}
}
}
On start, an Observable is created and logic to print some text is added to it. Then, an Observable with the generated data is created and a cache is added so that the result is replayed if the next subscription comes in after its results are generated. Then, a button is created. Then on button clicks a middle observable is chained with unique logic (it's a function that creates a function to append the value of i into the string, run with the current value of i; I tried to make something that couldn't just be reused) that is supposed to change with each click. Then the first Observable is subscribed to it so that the results of the whole chain end up being printed.
In theory, the cache operation takes care of not regenerating the data, and this works once, but onComplete is called on textObservable and then it can't be used again. It works if I subscribe it like this:
textSubscription = Some(start.map(((j: Int) => { (base: String) => s"${base} ${j}" })(i)).subscribe(text => textObservable.onNext(text)))
because the call to onComplete is intercepted, but this looks wrong and I wanted to know if there was a more typical way to do this, or architect it. It makes me think that I don't understand how this is supposed to be done if there isn't an out-of-the-box operation to do this.
Thank you.
I'm not 100% sure if I got the essence of your question right, but: if you have an Observable that may complete and you want to turn it into an Observable that never completes, you can just concatenate it with Observable.never.
For example:
// will complete after emitting those three elements:
val completes = Observable.from(List(1, 2, 3))
// will emit those three elements, but will never complete:
val wontComplete = completes ++ Observable.never
I'd like to have a generator that terminates, like python, but I can't tell from ranges::views::generate's interface if this is supported.
You can roll it by hand easily enough:
https://godbolt.org/z/xcGz6657r although it's probably better to use a coroutine generator if you have one available.
You can return an optional in the generator, and stop taking elements when a std::nullopt is generated with views::take_while
auto out = ranges::views::generate(
[i = 0]() mutable -> std::optional<int>
{
if (i > 3)
return std::nullopt;
return { i++ };
})
| ranges::views::take_while([](auto opt){ return opt.has_value();})
;
I'm trying to get steam app id and steam user id in my Unreal Engine 4 project in the following way:
if (SteamAPI_Init())
{
IOnlineSubsystem* ossBase = IOnlineSubsystem::Get();
FOnlineSubsystemSteam* oss = Cast<FOnlineSubsystemSteam*>(ossBase);
if (!oss) {
printText(TEXT("Steam Subsystem is down!"), FColor::Red.WithAlpha(255));
return;
}
auto SteamID = FString(std::to_string(SteamUser()->GetSteamID().ConvertToUint64()).c_str());
auto AppID = FString(std::to_string(oss->GetSteamAppId()).c_str());
But it is not possible to convert IOnlineSubsystem to FOnlineSubsystemSteam. So what is a correct way to obtain the instance of FOnlineSubsystemSteam?
The solution is to use static_cast:
FOnlineSubsystemSteam* oss = static_cast<FOnlineSubsystemSteam*>(ossBase);
This one works. It seems obvious to use UE4 Cast, but in this case it does not work.
Does Rust have a way to make a program pluggable. In C the plugins I create are .so files that I load with dlopen. Does Rust provide a native way of doing the same thing?
The Rust FAQ officially endorses libloading. Beyond that, there are three different options I know of:
Use the shared_library crate
Use the dylib crate.
Use std::dynamic_lib, which is deprecated since Rust 1.5. (These docs are no longer available in version 1.32; it's likely the feature has been dropped altogether by now.)
I haven't tried any of these, so I cannot really say which is best or what the pros/cons are for the different variants. I'd strongly advise against using std::dynamic_lib at least, given that it's deprecated and will likely be made private at some point in the future.
Exactly,
And below is the complete use case example:
use std::unstable::dynamic_lib::DynamicLibrary;
use std::os;
fn load_cuda_library()
{
let path = Path::new("/usr/lib/libcuda.so");
// Make sure the path contains a / or the linker will search for it.
let path = os::make_absolute(&path);
let lib = match DynamicLibrary::open(Some(&path)) {
Ok(lib) => lib,
Err(error) => fail!("Could not load the library: {}", error)
};
// load cuinit symbol
let cuInit: extern fn(u32) -> u32 = unsafe {
match lib.symbol("cuInit") {
Err(error) => fail!("Could not load function cuInit: {}", error),
Ok(cuInit) => cuInit
}
};
let argument = 0;
let expected_result = 0;
let result = cuInit(argument);
if result != expected_result {
fail!("cuInit({:?}) != {:?} but equaled {:?}",
argument, expected_result, result)
}
}
fn main()
{
load_cuda_library();
}
Yes. There's a module std::unstable::dynamic_lib that enables dynamic loading of libraries. It's undocumented, though, as it's a highly experimental API (everything in std::unstable is undocumented). As #dbaupp suggests, the source is the best documentation (current version is af9368452).
I have a service_echo function in a simple chat application which uses SockJS for implementing multi-user private chat. I created an ETS table for the list of online users. By storing SockJS session, I thought to send message to that Connection whenever I receive a message from a different Connection.
Here is my service_echo code.
service_echo(Conn, {recv, Data}, state) ->
Obj = mochijson2:decode(Data),
{struct, JsonData} = Obj,
Name = proplists:get_value(<<"name">>, JsonData),
A = ets:lookup(username,Name),
io:format("~p",[Conn]),
if
length(A) =:= 0 ->
ets:insert(username,{Name,Conn});
true ->
[{AA,BB}] = ets:lookup(username,Name),
BB:send(Data)
end,
io:format("hello");
Even though Conn and BB are same, still Conn:send(data) sends a valid data to the browser while BB:send(Data) does nothing and even does not show an error.
Since I'm a new to Erlang, please excuse me for any unintented mistakes.
First of all, let me advise you on never using length(A) =:= 0 for testing whether the list A is empty or not; if A a long list, counting its elements will cost you a lot, although the result will not actually be used. Use A =:= [] instead, simpler and better.
I don't understand why you're saying that Conn and BB are the same. This does not follow from the code that you have posted here. If Name is not in the table, you insert an entry {Name, Conn}. Otherwise, if Name exists in the table and is related to a single object BB, you assume that this BB is a module and you call the send function defined therein.
It could be that you're reading wrong the semantics of if --- if that's the case, don't let the true guard confuse you, this is how an if-then-else is written in Erlang. Maybe you wanted to have something like:
...
A = ets:lookup(username,Name),
if
A =:= [] ->
ets:insert(username,{Name,Conn})
end,
[{_,BB}] = ets:lookup(username,Name),
BB:send(Data)
...
or even better:
...
A = ets:lookup(T,Name),
if
A =:= [] ->
ets:insert(T,{Name,Conn}),
BB = Conn;
true ->
[{_,BB}] = A
end,
BB:send(Data)
...
On the other hand, it could be that I misunderstood what you're trying to do. If that's the case, please clarify.