How can I achieve a loop like this:
foobar.each(function (model, j) {
// asynchrounous call etc. {in here bool get set to true}
// outside all asynchronous calls
// wait till bool is true, without stopping anything else except the loop to the top of
the _.each
})
I asked a similar question yesterday. But it got marked as a duplicate when it wasn't the same case. Their solution did not achieve the same thing. Also generator functions were suggested which looked like it would work. But I can't use them with ecmascript 5
I've tried busy loops and set time out but they don't seem to work either
I've also tried this:
goto();
function goto() {
if (foo === true) {
//return true; /*I've tried with and without the return because the loops
doesn't need a return*/
} else {
goto();
}
}
What happens with the goto() method is it breaks. Giving me the right results for the first iterations then execution seems to stop altogether. 'foo' always gets set to true in normal execution though.
What you could do is implement a foreach yourself, where you execute your condition, and then on success callback go to the next item (but meanwhile the rest of the code will keep running.
var iteration = 0 //count the iteration of your asynchronous process
//start looping
loop(iteration)
function loop(iteration){
var model = foobar[iteration];
//exit your loop when all iterations have finished (assuming all foobar items are not undefined)
if (foobar[iteration] === undefined){
return;
}
//do what you want
//on success callback
iteration++;
loop(iteration);
//end success callback
}
Related
I am trying to make a while loop loop a statement exactly for one second after which it stops. I have tried this in DartPad, but it crashes the browser window.
void main(){
var count = 0.0;
bool flag = true;
Future.delayed(Duration(seconds: 1), (){
flag = false;
});
while (flag){
count++;
}
print(count);
}
Am I doing something wrong?
I like how you are trying to figure Futures out. I was exactly where you were before I understood this stuff. It's kind of like threads, but quite different in some ways.
The Dart code that you wrote is single threaded. By writing Future.delayed, you did not start a job. Its execution won't happen unless you let go of the thread by returning from this main function.
Main does not have to return if it is marked with async.
Two actions have to run "concurrently" to be able to interact with each other like you are trying to do. The way to do it is to call Future.wait to get a future that depends on the two futures. Edit: Both of these actions have to let go of execution at every step so that the other can get control of the single thread. So, if you have a loop, you have to have some kind of await call in it to yield execution to other actions.
Here's a modified version of your code that counts up to about 215 for me:
Future main() async {
var count = 0.0;
bool flag = true;
var futureThatStopsIt = Future.delayed(Duration(seconds: 1), (){
flag = false;
});
var futureWithTheLoop = () async {
while (flag){
count++;
print("going on: $count");
await Future.delayed(Duration(seconds: 0));
}
}();
await Future.wait([futureThatStopsIt, futureWithTheLoop]);
print(count);
}
Note for the readers: this question is specific for Codename One only.
I'm developing an app that needs some initial data from a server to run properly. The first shown Form doesn't need this data and there is also a splash screen on the first run, so if the Internet connection is good there is enought time to retrive the data... but the Internet connection can be slow or absent.
I have in the init a call to this method:
private void getStartData() {
Runnable getBootData = () -> {
if (serverAPI.getSomething() && serverAPI.getXXX() && ...) {
isAllDataFetched = true;
} else {
Log.p("Connection ERROR in fetching initial data");
}
};
EasyThread appInfo = EasyThread.start("APPINFO");
appInfo.run(getBootData);
}
Each serverAPI method in this example is a synchronous method that return true if success, false otherwise. My question is how to change this EasyThread to repeat again all the calls to (serverAPI.getSomething() && serverAPI.getXXX() && ...) after one second if the result is false, and again after another second and so on, until the result is true.
I don't want to shown an error or an alert to the user: I'll show an alert only if the static boolean isAllDataFetched is false when the requested data is strictly necessary.
I tried to read carefully the documentation of EasyThread and of Runnable, but I didn't understand how to handle this use case.
Since this is a thread you could easily use Thread.sleep(1000) or more simply Util.sleep(1000) which just swallows the InterruptedException. So something like this would work:
while(!isAllDataFetched) {
if (serverAPI.getSomething() && serverAPI.getXXX() && ...) {
isAllDataFetched = true;
} else {
Log.p("Connection ERROR in fetching initial data");
Util.sleep(1000);
}
}
I am facing a weird case, I am using google directionsService.route. but it doesn’t sync well. Here is my code:
angular.forEach(requestArray, function(v, i) {
directionsService.route(v, function(result, status) {
var googleLeg = result.routes[0].legs[0];
// sth else...
});
});
As you can see, I am looping the location Array into the route. every time I fire the function, it will go through the requestArray first, (if we make a breakpoint on the line (var googleLeg = result.routes[0].legs[0]), it doesn’t reach there until it goes through all the requestArray.(i from 0 - length); then it will have the second loop for directionsService.route( at this time, it will reach to line(var googleLeg = result.routes[0].legs[0]); Any idea about this?
Essentially your problem is that calling a google service is an asynchronous call, and you are not guaranteed when the callback will execute. If you need to process requestArray synchronously, here is what you can do:
function start() {
// create a copy of request array
var stuff = [].slice.call(requestArray);
function continueSync() {
// stop the recursion if we have nothing left to process
if (!stuff || stuff.length == 0) return;
// grab the first item off of the stuff queue
v = stuff[0];
stuff = stuff.slice(1);
// call to google
directionsService.route(v, function(result, status) {
var googleLeg = result.routes[0].legs[0];
// sth else...
// now continue processing the rest of the stuff queue through tail recursion
continueSync();
});
}
// kick off our recursive processing
continueSync();
}
your problem is that calling a google service is an asynchronous call, you could prove to generate threads
I have a piece of code wrapped in try-catch in order to catch an exception, but I want to re-try that piece of code until it is successful. I have added a loop based on this post. This works as far as looping the code, however it is an infinite loop. Once the code is successful and moves to the next page, the code is still looping and ends up failing because it is searching for a locator that is no longer available because the page has advanced to the next. My question is this: how do I break out of the loop once the code is successful?
int count = 0;
int maxTries = 1;
while (true)
{
try{
driver.FindElement(By.id("textbox").sendKeys("123");
driver.FindElement(By.id("submit").click();
driver.FindElement(By.id("catalog").click();
if(driver.getTitle().equals("Correct Page"))
{break;
}
}
catch(NoSuchElementException e)
{
if (++count == maxTries) throw e;
}
}
}
driver.FindElement(By.id("part1").click();
Maybe using an exception for this purpose is not the right route.
Instead of while (true), try while (!driver.getTitle().equals("Correct Page"))
Then within the loop, increment the count, check it against maxTries and break when it is exceeded
I'd like to perform an asynch function conditionally, but I think I'm missing the correct syntax to say what I want.
this.doUpToThreeThings = function(skipTheMiddleStep) {
return doFirstThing().then(function (result) {
if (skipTheMiddleStep) {
return doThirdThing();
} else {
return doSecondThing();
}
}).then(function (result) {
if (skipTheMiddleStep) {
return "ok"; // return what?
} else {
return doThirdThing();
}
});
}
By the time we get to the second then, I don't know if the first block did the middle step, so I'm forced into repeating the condition. And the second block reads weird: it should say, if skip the middle step, then do the third thing, but since it we know that the previous block must have done the third thing, it just returns. So I have to repeat the condition and write pretty wrong-looking code in the second then.
I realize I can write a function called doSecondAndThirdThings, and just call that from the condition in the first block, but that's not really DRY, it's just hiding the non-DRYness. (or maybe I'm wrong about that?)
Also, I'm still a little confused about returning a completed promise on that "ok" branch. Is that right how it is, or should I say something like resolve? -- Thanks
The deferred in thefourtheye's answer is pointless and is considered an anti pattern with promises.
Here is how I would do it:
this.doUpToThreeThings = function(skipTheMiddleStep) {
return doFirstThing().then(function (result) {
return (skipTheMiddleStep) ? doThirdThing() : doSecondThing().then(doThirdThing);
});
}