I have been looking for an answer for this for a while now, but have not yet found any. I have a method that looks like this
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("ShowNextView", sender: nil)
}
Is it possible in some way to use the performSelectorOnMainThread for this purpose? As I can see performSelectorOnMainThread on accepts one parameter.
Have you tried to set the sender to self instead of nil?
dispatch_async(dispatch_get_main_queue(),{
self.performSegueWithIdentifier("ShowNextView",sender: self)
})
did you try this?
let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
dispatch_async(dispatch_get_main_queue()) {
self.performSegueWithIdentifier("ShowNextView", sender: nil)
}
}
Related
Actually I'm returing a cloned struct
pub fn matrix_first_or_create(&self, schema: String, symbol: String) -> RewardMatrix {
....
let rewards = reward_matrix
.filter(state.eq(schema.clone()))
.filter(turn_symbol.eq(symbol.clone()))
.limit(1)
.load::<RewardMatrix>(&self.connection)
.expect("Error loading posts");
if rewards.len() > 0 {
return rewards.get(0).unwrap().clone();
}
....
}
Is this the right way to handle a result in Diesel? Can I "extract" and own the first and only result from this query?
What you need here is the .first() method of the RunQueryDsl trait.
Here is an example of how it works:
let reward: RewardMatrix = reward_matrix
.filter(state.eq(schema.clone()))
.filter(turn_symbol.eq(symbol.clone()))
.first(&self.connection)?;
But if your query may not return that row, it’s also good to use the .optional() method of QueryResult:
let reward: Option<RewardMatrix> = reward_matrix
.filter(state.eq(schema.clone()))
.filter(turn_symbol.eq(symbol.clone()))
.first(&self.connection)
.optional()?;
load returns a simple owned Vec<RewardMatrix>, so any solution for getting an owned element from a Vec works here:
if let Some(reward) = rewards.into_iter().next() {
return reward;
}
but Diesel also provides better-suited alternatives like get_result and first that don’t involve Vec at all (combine with optional as recommended in the documentation):
let reward = reward_matrix
.filter(state.eq(&schema))
.filter(turn_symbol.eq(&symbol))
.first::<RewardMatrix>(&self.connection)
.optional()
.expect("Error loading posts");
if let Some(reward) = reward {
return reward;
}
I'm attempting to do something that I feel is pretty basic: I have a pulldown, and I'd like the onchange event for that pulldown to cause the program to fetch some data from the backend based on the user's input. (And then, you know, give the user more options based on the first thing they picked. Really simple, and seems like I ought to have been able to find an easy way to do this.)
Full code for this minimal (failing) example is at: https://github.com/djmcmath/broken-yew
But the relevant bit, which doesn't behave correctly, is below:
The view function renders, delightfully, an iterated list. I pass in a callback, so it knows what to do on the "onchange" event.
The callback gets executed, which makes me very happy. But it isn't calling the Msg::GetData. This compiles, which is nice, but it doesn't work, which is less nice.
I've spent, I'm ashamed to admit, several weeks of my spare time fighting with this. I think it has something to do with scopes and lifetimes. I think that the way I'm making this compile -- by cloning the context and using "move" disconnects it from the actual context that I need to make this work. But every variation on the theme that I've been able to find in examples and references complains about scope or lifetimes.
Thanks in advance for the help.
fn update(&mut self, ctx: &Context<Self>, msg: Self::Message) -> bool {
match msg {
Msg::GetData(value) => {
log::info!("Start 'fetch' with user-selected value: {}", value);
ctx.link().send_future(async {
match fetch_markdown("url_shortened_for_clarity").await {
Ok(md) => Msg::SetMarkdownFetchState(FetchState::Success(md)),
Err(err) => Msg::SetMarkdownFetchState(FetchState::Failed(err)),
}
});
false
},
Msg::SetMarkdownFetchState(fetch_state) => {
let mut wr = WebReturn { term_id: 0, dow: 0, dep_time_num: 0 };
match fetch_state {
FetchState::Success(s) => { wr = serde_json::from_str(&s).expect(&format!("Poorly formatted JSON! {}", s).to_string()); },
FetchState::Failed(f) => { log::info!("Fetch failed: {}", f); },
FetchState::NotFetching => {},
FetchState::Fetching => {}
};
log::info!("term_id (3) : {}, dep_time_num (12000) : {}, and dow (3) : {}", wr.term_id, wr.dep_time_num, wr.dow);
true
}
}
}
fn view(&self, ctx:&Context<Self>) -> Html {
let ctx_link = ctx.link().clone();
let my_callback: Callback<String> = Callback::from(move |value: String| {
let val_as_num = value.parse::<i32>().unwrap_or(0);
log::info!("Returned value: {}", val_as_num);
ctx_link.callback(|val_as_num: i32| Msg::GetData(val_as_num));
});
html! {
<div>
{ self.render_list(&self.props.term_list, my_callback) }
</div>
}
}
This line does not "call back" to your component, it creates a callback and then doesn't call it:
ctx_link.callback(|val_as_num: i32| Msg::GetData(val_as_num));
You need to instead call .send_message() in your callback or, better yet, create your original callback with .callback():
let my_callback = ctx_link.callback(|value: String| {
let val_as_num = value.parse::<i32>().unwrap_or(0);
log::info!("Returned value: {}", val_as_num);
Msg::GetData(val_as_num)
});
I'm still rather new to Rust and have a hard time wrapping my head around futures. I want to implement a "timer app" in the browser and to do so I'm using https://yew.rs/. For the timer I tried to use https://github.com/tomaka/wasm-timer/, but there are not docs and no examples. Looks like the usage is supposed to be obvious, but I don't get it.
I assume that I have to do something like:
let i = Interval::new(core::time::Duration::from_millis(250));
This should create an Interval that fires every 250ms. But what is fired? How to I specify my callback? I would expect something like:
i.somehow_specify_callback(|| { ... executed every 250ms ...});
My feeling is, that I'm somehow on the wrong path and do not get grasp Rust futures. A working example on how to make an Interval execute some code would be very appreciated.
Here is a pseudo code example for Timer component:
enum SecondsStateAction {
Increment,
}
#[derive(Default)]
struct SecondsState {
seconds: usize,
}
impl Reducible for SecondsState {
/// Reducer Action Type
type Action = SecondsStateAction;
/// Reducer Function
fn reduce(self: Rc<Self>, action: Self::Action) -> Rc<Self> {
match action {
SecondsStateAction::Increment => Self { seconds: self.seconds + 1 }.into(),
}
}
}
#[function_component(Timer)]
pub fn timer() -> Html {
let seconds_state_handle = use_reducer(SecondsState::default);
use_effect_with_deps(
{
let seconds_state_handle = seconds_state_handle.clone();
move |_| {
// i intervals get out of scope they get dropped and destroyed
let interval = Interval::new(1000, move || seconds_state_handle.dispatch(SecondsStateAction::Increment));
// So we move it into the clean up function, rust will consider this still being used and wont drop it
// then we just drop it ourselves in the cleanup
move || drop(interval)
}
},
(), // Only create the interval once per your component existence
);
html! {<h1>{*seconds_state_handle}{" seconds has passed since this component got rendered"}</h1>}
}
to learn more about the hooks i used in the code visit https://yew.rs/docs/concepts/function-components/pre-defined-hooks
Is there a more idiomatic way to express something like the following?
fn main() {
let mut foo: Option<u8> = None;
match foo {
Some(foo_val) if ! (foo_val < 5) /* i.e. the negation of my acceptance condition */ => {}
_ => { foo.replace(5); }
}
}
It seems like most of the time there's an alternative to having an arm that doesn't do anything, but I've been unable to find one for this particular case.
What I'd like to say is the more direct if foo.is_none() || /* some way to extract and test the inner value */ { ... }, or perhaps some chaining trick that's eluding me.
// in None case
// │ in Some(_) case
// ┌┴─┐ ┌───────────────────┐
if foo.map_or(true, |foo_val| foo_val < 5) {
// ...
}
For more information see Option::map_or.
There are many ways to do it. One of the simplest (and arguably most readable) is something like this:
if foo.unwrap_or(0) < 5 {
...
}
The above will be true in both cases:
when foo is Some with a value smaller than 5;
when foo is None.
In some more complex scenarios, where the "default" value needs to be calculated and performance is critical, you might want to consider unwrap_or_else.
As Lukas suggested, the map_or method can also be used. Note that arguments passed to map_or are eagerly evaluated, so if performance is critical, you might want to consider map_or_else as an alternative.
You can do it with filter (using the negation of your condition) and is_none:
if foo.filter(|&x| !(x < 5)).is_none() {
// Here either foo was None or it contained a value less than 5
}
I'm not sure I completely understand your question but you can try something like that:
fn main() {
let foo: Option<u8> = None;
let result = foo.filter(|foo_val| !(*foo_val < 5) ).unwrap_or(5);
println!("Result: {result}");
}
More example on Playground
The matches! macro seems like a good fit:
if !matches!(foo, Some(a) if a>=5) { foo.replace(5) }
Rust Playground
I'll throw in another solution just for fun....
foo = foo.
or(Some(5)). // if None return Some(5)
map(|x| if x<5 { 5 } else { x });
or (for this specific example)
foo = foo.
or(Some(5)). // if None return Some(5)
map(|x| u8::max(x, 5));
With filter and or,
foo = foo.filter(|a| *a >= 5)
.or(Some(5));
There is the unstable method Option::is_some_and that has been built for exactly this purpose:
if foo.is_some_and(|foo_val| foo_val < 5) {
// ...
}
As it's unstable, it's currently only usable on nightly. See the tracking issue for up to date information.
i've created my first substrate project successful and the built pallet also works fine. Now i wanted to create tests for the flow and the provided functions.
My flow is to generate a random hash and store this hash associated to the sender of the transaction
let _sender = ensure_signed(origin)?;
let nonce = Nonce::get();
let _random_seed = <randomness_collective_flip::Module<T>>::random_seed();
let random_hash = (_random_seed, &_sender, nonce).using_encoded(T::Hashing::hash);
ensure!(!<Hashes<T>>::contains_key(random_hash), "This new id already exists");
let _now = <timestamp::Module<T>>::get();
let new_elem = HashElement {
id: random_hash,
parent: parent,
updated: _now,
created: _now
};
<Hashes<T>>::insert(random_hash, new_pid);
<HashOwner<T>>::insert(random_hash, &_sender);
Self::deposit_event(RawEvent::Created(random_hash, _sender));
Ok(())
works good so far, when now i want to test the flow with a written test, i want to check if the hash emitted in the Created event is also assigned in the HashOwner Map. For this i need to get the value out of the event back.
And this is my problem :D i'm not professional in rust and all examples i found are expecting all values emitted in the event like this:
// construct event that should be emitted in the method call directly above
let expected_event = TestEvent::generic_event(RawEvent::EmitInput(1, 32));
// iterate through array of `EventRecord`s
assert!(System::events().iter().any(|a| a.event == expected_event));
When debugging my written test:
assert_ok!(TemplateModule::create_hash(Origin::signed(1), None));
let events = System::events();
let lastEvent = events.last().unwrap();
let newHash = &lastEvent.event;
i see in VSCode that the values are available:
debug window of vs code
but i dont know how to get this Hash in a variable back... maybe this is only a one liner ... but my rust knowledge is damn too small :D
thank you for your help
Here's a somewhat generic example of how to parse and check events, if you only care about the last event that your module put in system and nothing else.
assert_eq!(
System::events()
// this gives you an EventRecord { event: ..., ...}
.into_iter()
// map into the inner `event`.
.map(|r| r.event)
// the inner event is like `OuterEvent::mdouleEvent(EventEnum)`. The name of the outer
// event comes from whatever you have placed in your `delc_event! {}` in test mocks.
.filter_map(|e| {
if let MetaEvent::templateModule(inner) = e {
Some(inner)
} else {
None
}
})
.last()
.unwrap(),
// RawEvent is defined and imported in the template.rs file.
// val1 and val2 are things that you want to assert against.
RawEvent::Created(val1, val2),
);
Indeed you can also omit the first map or do it in more compact ways, but I have done it like this so you can see it step by step.
Print the System::events(), this also helps.
I now got it from the response of kianenigma :)
I wanted to reuse the given data in the event:
let lastEvent = System::events()
// this gives you an EventRecord { event: ..., ...}
.into_iter()
// map into the inner `event`.
.map(|r| r.event)
// the inner event is like `OuterEvent::mdouleEvent(EventEnum)`. The name of the outer
// event comes from whatever you have placed in your `delc_event! {}` in test mocks.
.filter_map(|e| {
if let TestEvent::pid(inner) = e {
Some(inner)
} else {
None
}
})
.last()
.unwrap();
if let RawEvent::Created(newHash, initiatedAccount) = lastEvent {
// there are the values :D
}
this can maybe be written better but this helps me :)