What is the equivalent of the following code in Xamarin.iOS?
dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
//Background Thread
dispatch_async(dispatch_get_main_queue(), ^(void){
//Run UI Updates
});
});
Here's pretty much the C# equivalent of your code:
using CoreFoundation;
DispatchQueue.GetGlobalQueue(DispatchQueuePriority.Default).DispatchAsync(() =>
{
DispatchQueue.MainQueue.DispatchAsync(() => { });
});
Related
I'm not sure of how to adequately achieve my desired control flow using promises/bluebird.
Essentially I have a database with X 'tasks' stored and each needs to be loaded and executed sequentially. I don't want to run more than one task concurrently and the entire code must continue executing indefinitely.
I have achieved this with the following code so far:
export default function syncLoop() {
getNextTaskRunner().then((taskRunner) => {
if (taskRunner) {
taskRunner.startTask()
.then(syncLoop)
.catch((error) => {
throw new Error(error);
});
} else {
syncLoop();
}
});
}
getNextTaskRunner() simply loads and resolves with the next task from the database (calc'd based on timestamps). Or it resolves with null (no task avail).
taskRunner.startTask() resolves with null when the full task has completed.
I've been advised that the way it is structured (recursive /w promises) could lead to stack issues after it has been running for some time.
What I've thought about doing is to restructure it to something like:
let running = false;
setInterval(() => {
if (!running) {
running = true;
getNextTaskRunner().then((taskRunner) => {
if (taskRunner) {
taskRunner.startTask()
.then(() => {
running = false;
})
.catch((error) => {
log.error(error);
});
} else {
running = false;
}
});
}
}, 5000);
Or as yet another possibility, using event emitters in some form?
task.on('complete', nextTask());
Thoughts and advice will be greatly appreciated!
What stack issues? The way you've written your code is perfectly fine as long as getNextTaskRunner is truly async (i.e. it gives control back to the main loop at some point, e.g. if it does async io). There is no recursion in your code in that case. Whoever told you that is mistaken.
Though you might want to add a setTimeout somewhere so you won't flood your db with requests. Plus it will help you if getNextTaskRunner will no longer be sync (due to for example in memory caching):
export default function syncLoop() {
setTimeout(() => {
getNextTaskRunner().then((taskRunner) => {
if (taskRunner) {
taskRunner.startTask()
.then(syncLoop)
.catch((error) => {
throw new Error(error);
});
} else {
syncLoop();
}
});
}, 2000);
}
Assume that I have a Collection called Tasks which has few tasks in it.I call a method to return a task array to the user but for some reason it doesn't return anything.
Here is a code for example:
if (Meteor.isClient) {
// This code only runs on the client
Template.body.helpers({
tasks: function () {
// Show newest tasks first
Meteor.call("getTasks", function(error, result) {
return result; // Doesn't do anything..
});
}
});
}
Meteor.methods({
getTasks: function() {
return Tasks.find({}, {sort: {createdAt: -1}});
}
});
Any ideas why when I call the method it doesn't return anything?
Tasks.find() returns a cursor, which makes no sense to transmit to the client via DDP.
You probably mean to return Tasks.find().fetch(), but that defeats the purpose of Meteor's very nice data synchronization mechanism.
Have you read Understanding Meteor's publish/subscribe?
I need to show a ext lib Dialog after the user select a combobox (I use a Select2 of BootStrap for XPages).
The alert code function work well, but the XSP.openDialog not .
I've found a old stackoverflow question about this but I don't understand how can I solve my problem. Any ideas?
Tnx a lot
$(document).ready(
function() {
x$("#{id:comboBox1}").select2().on("change", function(e) {
XSP.allowSubmit();
XSP.partialRefreshPost("#{id:divView}",{
onStart: function () {
// do something when the partial update is finished
//alert("start...") -- this WORK
XSP.openDialog("#{id:dialog1}"); //this doesn't work
},
onComplete: function () {
// do something when the partial update is finished
//alert("stop...") -- THIS WORK
XSP.closeDialog("#{id:dialog1}"); //this doesn't work
}
});
} )
}
);
I've found a solution with XSP.allowSubmit();, magic Sven Hasselbach!:
$(document).ready(
function() {
x$("#{id:comboBox1}").select2().on("change", function(e) {
XSP.partialRefreshPost("#{id:divView}",{
onStart: function () {
// do something when the partial update is finished
//alert("start...") -- this WORK
XSP.allowSubmit();
XSP.openDialog("#{id:dialog1}");
},
onComplete: function () {
// do something when the partial update is finished
//alert("stop...") -- THIS WORK
XSP.allowSubmit();
XSP.closeDialog("#{id:dialog1}");
}
});
} )
}
);
I am trying to load an image using the fromURL. The issue is that I'd like it to be able to load a default icon if it is not able to reach the Image server to download the image. Looking at the docs I did not see an error callback for the fromURL function. How are we supposed to catch that the call was not successful and therefore do the appropriate thing? It does not seem that the callback gets called at all when image load was unsuccessful.
You can use fabric.util.loadImage() method instead of fabric.Image.fromURL().
If you look at the fromURL() method implementation, internally it uses the loadImage().
The following code may help you:
fabric.util.loadImage('https://s3-eu-west-1.amazonaws.com/kienzle.dev.cors/img/image2.png', function(img) {
if(img == null) {
alert("Error!");
}else {
var image = new fabric.Image(img);
canvas.add(image).setActiveObject(image);
canvas.renderAll();
}
}, { crossOrigin: 'anonymous' });
Here is the fiddle: http://jsfiddle.net/k7moorthi/30kmn5kL/
once you have done the function, even if theres a mistake the callback keeps running, then you could check for the element (as other said) in this way:
let fabricBackgroundInstance = new fabric.Image.fromURL(imageToUse, (oImg) => {
if(oImg._element == null){
console.error('oImg', oImg._element);
return;
}
You could use getElement() to check this error.
fabric.Image.fromURL('/foo.jpg', (img) => {
if (img.getElement() === undefined) {
console.log('Failed to load image!');
return;
}
// do something on success
}
You can add the second argument isError to your callback function.
fabric.Image.fromURL("your image URL", (img, isError) => {
if (isError) {
console.log('Something Wrong with loading image');
return;
}
// do something on success
}
Also check fabric.js source code of Image.fromURL http://fabricjs.com/docs/fabric.js.html#line21471
Specifically when doing MonoDroid uses of threads all the documentation I can find recommends calling RunOnUiThread() to call the callback. There is a similar function that can be used on MonoTouch however both of them require a GUI (Activity or whatever its counter part is on IOS). What I would like is to be able to start a thread, pass in a callback and call that callback on the thread that started the thread. For example
ThreadPool.QueueUserWorkItem(state =>
{
//Do Stuff
execute_callback_magically_on_main_thread(() => callback(response));
});
Any ideas? To be clear I would prefer this to not need a handle to the Activity etc.
What if you do something like this? (assuming they have the same signature) I haven't messed with RunOnUiThread, so I don't know it's signature.
public delegate void InvokeOnUIMethod(Action action);
public void CallingMethod()
{
//iOS
MyMethod(InvokeOnMainThread, () => { /* Your callback functionality */ });
//Android
MyMethod(RunOnUiThread, () => { /* Your callback functionality */ });
}
public void MyMethod(InvokeOnUIMethod execute_callback_magically_on_main_thread, Action callback)
{
System.Threading.ThreadPool.QueueUserWorkItem(state =>
{
//Do Stuff
execute_callback_magically_on_main_thread(() => callback(response));
});
}
I hope this helps.
Using the Alpha builds (Hopefully soon to be available as stable) you can use the new Async await idiom.
here is an overview on MSDN:
http://msdn.microsoft.com/en-gb/library/vstudio/hh191443.aspx
and here is a great video series on Channel9:
http://channel9.msdn.com/Series/Three-Essential-Tips-for-Async/Tip-1-Async-void-is-for-top-level-event-handlers-only
I found a solution that works and does not appear to be dependent on either platform.
Task<string> t = new Task<string>(() =>
{
//Do Stuff
return "my results";
});
t.ContinueWith(task =>{
if(callback != null)
callback(task.Result);
}, TaskScheduler.FromCurrentSynchronizationContext());
t.Start();
The important part is the TaskScheduler.FromCurrentSynchronizationContext() which tells the "ContinueWith" to execute on the original thread.