I have an issue with some code that looks like this. In this form I have an error
The expression here has a type of 'void', and therefore can't be used.
Try checking to see if you're using the correct API; there might be a function or call that returns void you didn't expect. Also check type parameters and variables which might also be void.dart(use_of_void_result).
If I remove the .onDone() the error goes away. Why? ELI5 please :-)
I was looking at https://api.dart.dev/stable/2.7.0/dart-async/Stream/listen.html but seem to still be misundertanding something.
I also read https://api.dart.dev/stable/2.7.0/dart-async/StreamSubscription/onDone.html
serviceName.UploadThing(uploadRequest).listen((response) {
uploadMessageOutput = response.message;
if (response.uploadResult) {
showSuccess();
} else {
showError();
}
getUploadFileList(event);
isSaveInProgress = false;
}).onError((error) {
isSaveInProgress = false;
_handleFileUploadError(uploadRequest, error);
}).onDone(() {
isSaveInProgress = false;
});
Your code is almost right, but will only require a simple change to work correctly.
You would be seeing the same error if you swapped the ordering of onError and onDone, so the issue has nothing to do with your stream usage. However, you're attempting to chain together calls to onError and then onDone which won't work since both of these methods return void.
What you're looking for is cascade notation (..), which will allow for you to chain calls to the StreamSubscription returned by listen(). This is what your code should look like:
serviceName.UploadThing(uploadRequest).listen((response) {
uploadMessageOutput = response.message;
if (response.uploadResult) {
showSuccess();
} else {
showError();
}
getUploadFileList(event);
isSaveInProgress = false;
})..onError((error) { // Cascade
isSaveInProgress = false;
_handleFileUploadError(uploadRequest, error);
})..onDone(() { // Cascade
isSaveInProgress = false;
});
Related
I'm trying to transform a Stream of a list of one type into a Stream of a list of another type, and having an issue with this.
I have this list of Habits that I'm streaming from Firebase, and I want to accept that stream in a function, and return a new stream that is a list of ViewModels of another type from it. But my function is returning a stream of the wrong type.
Here is my code:
Stream<List<HabitCompletionViewModel>> _getTodaysHabits(
Stream<List<Habit>> habitsStream) {
var result = habitsStream.map((habitsList) {
habitsList.map(
(habit) async {
await _getHabitCompletionsCurrent(habit);
HabitCompletion completion = habit.completions!.firstWhere(
(completion) => completion.date
.dayEqualityCheck(DateTime.now().startOfDate()));
return HabitCompletionViewModel(completion: completion, habit: habit);
},
).toList();
});
return result;
}
I am getting a compile error because the result variable is showing as type Stream<Null> when I hover over it, where I would expect it to be Stream<List<HabitCompletionViewModel>>. Any idea what I'm doing wrong?
Your outer .map call does not have a return statement which is why you are getting a Stream<Null>.
So add a return statement like so:
Stream<List<HabitCompletionViewModel>> _getTodaysHabits(
Stream<List<Habit>> habitsStream) {
var result = habitsStream.map((habitsList) {
// added return statement here
return habitsList.map(
(habit) async {
await _getHabitCompletionsCurrent(habit);
HabitCompletion completion = habit.completions!.firstWhere(
(completion) =>
completion.date.dayEqualityCheck(DateTime.now().startOfDate()));
return HabitCompletionViewModel(completion: completion, habit: habit);
},
).toList();
});
return result;
}
However the above code still has an error because it is now returning a Stream<List<Future<HabitCompletionViewModel>>> instead of the desired Stream<List<HabitCompletionViewModel>>. To solve this you can use .asyncMap instead of .map.
Stream<List<HabitCompletionViewModel>> _getTodaysHabits(
Stream<List<Habit>> habitsStream) {
var result = habitsStream.asyncMap((habitsList) {
return Stream.fromIterable(habitsList).asyncMap(
(habit) async {
await _getHabitCompletionsCurrent(habit);
HabitCompletion completion = habit.completions!.firstWhere(
(completion) =>
completion.date.dayEqualityCheck(DateTime.now().startOfDate()));
return HabitCompletionViewModel(completion: completion, habit: habit);
},
).toList();
});
return result;
}
I was re-reading this post here: https://stackoverflow.com/a/24473888/1828637
And got concerned about if I did things correctly. This is how I do unloading:
So I set up some stuff per window. And unload them on shutdown. (i dont unload on window close, i havent found a need to yet, as when it closes, everything i added to it goes with with the close [such as my mutation observers]).
All code below is theoretical, the mutation stuff is example, so there might be typos or bugs in it. I was wondering if the idea behind it is appropriate:
var unloadersOnShutdown = [];
var unloadersOnClose = [];
function startup() {
let DOMWindows = Services.wm.getEnumerator(null);
while (DOMWindows.hasMoreElements()) {
let aDOMWindow = DOMWindows.getNext();
var worker = new winWorker(aDOMWindow);
unloadersOnShutdown.push({DOMWindow: aDOMWindow, fn: worker.destroy});
}
}
function shutdown() {
Array.forEach.call(unloadersOnShutdown, function(obj) {
//should probably test if obj.DOMWindow exists/is open, but just put it in try-ctach
try {
obj.fn();
} catch(ex) {
//window was probably closed
console.warn('on shutdown unlaoder:', ex);
}
});
}
function winWorker(aDOMWindow) {
this.DOMWindow = aDOMWindow;
this.init();
}
winWorker.prototype = {
init: function() {
this.gMutationObserver = new this.DOMWindow.MutationObserver(gMutationFunc.bind(this));
this.myElement = this.DOMWindow.querySelector('#myXulEl');
this.gMutationObserver.observe(this.myElement, gMutationConfig);
if (this.DOMWindow.gBrowser && this.DOMWindow.gBrowser.tabContainer) {
this.onTabSelectBinded = this.onTabSelect.bind(this);
this.gBrowser.tabContainer.addEventListener('TabSelect', this.onTabSelectBinded, false);
}
},
destroy: function() {
this.gMutationObserver.disconnect();
if (this.onTabSelectBinded) {
this.gBrowser.tabContainer.removeEventListener('TabSelect', this.onTabSelectBinded, false);
}
},
onTabSelect: function() {
console.log('tab selected = ', thisDOMWindow.gBrowser.selectedTab);
}
};
var windowListener = {
onOpenWindow: function (aXULWindow) {},
onCloseWindow: function (aXULWindow) {
var DOMWindow = aXULWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowInternal || Ci.nsIDOMWindow);
for (var i=0; i<unloadersOnClose.length; i++) {
if (unloadersOnClose.DOMWindow == DOMWindow) {
try {
unloadersOnClose.fn();
} catch(ex) {
console.warn('on close unloader:', ex);
}
unloadersOnClose.splice(i, 1);
i--;
}
}
},
onWindowTitleChange: function (aXULWindow, aNewTitle) {},
}
I think one problem is me not using weak references with DOMWindows but I'm not sure.
The idea around unloaders in general seems to be OK, but very limited (to windows only).
The implementation is lacking. E.g. there is a big, fat bug:
unloadersOnShutdown.push({DOMWindow: aDOMWindow, fn: worker.destroy});
// and
obj.fn();
// or
unloadersOnClose.fn();
This will call winWorker.prototype.destroy with the wrong this.
The i++/i-- loop also looks, um... "interesting"?!
Also, keep in mind that there can be subtle leaks, so you should mind and test for Zombie compartments.
Not only can a window leak parts of your add-on (e.g. bootstrap.js) but it is also possible to leak closed windows by keeping references in your add-on. And of course, it's not just windows you need to care about, but also e.g. observers, other types of (XPCOM) listeners etc.
I know event.type in DOM. I can parse for example mouseup, keydown, touchstart and so on. But how can I check for the event subclass? Like MouseEvent, AnimationEvent or ClipboardEvent? Can I use the event.type property?
You can check the class like
void myHandler(Event e) {
if(e is MouseEvent) {
print('Mouse');
} else if(e is AnimationEvent) {
print('Animation');
} else if(e is KeyboardEvent) {
print('Keyboard');
}
}
Since JavaScript is a prototype-based language you can to do it a bit strangely using Object.prototype.toString.call() and then cleaning up the result a little, like this:
var button = document.getElementById("testEvent");
button.onclick = function(e) {
console.log(
Object.prototype.toString.call(e).replace(/^\[object ([^\]]*)\]/, "$1")
);
}
This fiddle shows it in action - http://jsfiddle.net/SrmGJ/1/ working for me in FireFox. It should output "MouseEvent" in the fiddle, but if you hook it up to some of the other events, you will see different results.
Another method would be to call EventType.prototype.isPrototypeOf(e) for each of the types:
...
if (MouseEvent.prototype.isPrototypeOf(e)) { console.log("MouseEvent"); }
if (AnimationEvent.prototype.isPrototypeOf(e)) { console.log("AnimationEvent"); }
if (KeyboardEvent.prototype.isPrototypeOf(e)) { console.log("KeyboardEvent"); }
...
But that would look pretty nasty IMHO.
I think I've gotten the most simplest scenario built. I just want to pass it by everyone for a sanity check. Here's the idea:
GetErrorCodes.cfm does the following:
<cfscript>
response = new ErrorCodes().WhereXXX(); // ACF or Railo, doesn't matter
</cfscript>
ErrorCodes.cfc:
function WhereXXX() {
return new sproc().exec('app.GetErrorCodes'); // All my functions will do this instead of executing the sproc themselves.
}
sproc.cfc:
component {
function exec(procedure) {
local.result = {};
if (server.ColdFusion.productname == 'Railo') {
return new Railo().exec(arguments.procedure); // Has to be outside of sproc.cfc because ColdFusion throws a syntax error otherwise.
}
local.svc = new storedProc();
local.svc.setProcedure(arguments.procedure);
local.svc.addProcResult(name='qry');
try {
local.obj = local.svc.execute();
local.result.Prefix = local.obj.getPrefix();
local.result.qry = local.obj.getProcResultSets().qry;
} catch(any Exception) {
request.msg = Exception.Detail;
}
return local.result;
}
Railo.cfc:
component {
function exec(procedure) {
local.result = {};
try {
storedproc procedure=arguments.procedure result="local.result.Prefix" returncode="yes" {
procresult name="local.result.qry";
}
} catch(any Exception) {
request.msg = Exception.Message;
}
return local.result;
}
}
So I've been working on this all day, but tell me, is this a sane way to keep the source code the same if it's to be run on either a ColdFusion server or a Railo server?
Um... just use <cfstoredproc> instead of trying to use two different CFScript approaches that are mutually exclusive to each other of the CFML platforms.
I'm trying to build a streaming .mp3 player to run various sound files on my web site. To do that, I followed a tutorial that includes a code template at:
http://blog.0tutor.com/post.aspx?id=202&title=Mp3%20player%20with%20volume%20slider%20using%20Actionscript%203
However, whether I preserve the template's direction to the author's own sound file or insert my own direction to my online sound file, I keep on running into glitches in the ActionScript that I can't fathom.
Those errors are:
1084: Syntax error: expecting rightparen before _.
1086: Syntax error: expecting semicolon before rightparen.
When I try to correct them, I get new errors. I can't determine whether the sound file is loading; it certainly never plays. The volume slider does not work.
I did find one line that looked like it should have been commented out, the one that reads
to start at the same place
So I tried commenting that out. No dice. Same errors.
Thanks in advance for any suggestions. Code follows:
var musicPiece:Sound = new Sound(new URLRequest _
("http://blog.0tutor.com/JeffWofford_Trouble.mp3"));
var mySoundChannel:SoundChannel;
var isPlaying:Boolean = false;
to start at the same place
var pos:Number = 0;
play_btn.addEventListener(MouseEvent.CLICK, play_);
function play_(event:Event):void {
if (!isPlaying) {
mySoundChannel = musicPiece.play(pos);
isPlaying = true;
}
}
pause_btn.addEventListener(MouseEvent.CLICK, pause_);
function pause_(event:Event):void {
if (isPlaying) {
pos = mySoundChannel.position;
mySoundChannel.stop();
isPlaying = false;
}
}
stop_btn.addEventListener(MouseEvent.CLICK, stop_);
function stop_(event:Event):void {
if (mySoundChannel != null) {
mySoundChannel.stop();
pos = 0;
isPlaying = false;
}
}
var rectangle:Rectangle = new Rectangle(0,0,100,0);
var dragging:Boolean = false;
volume_mc.mySlider_mc.addEventListener(MouseEvent.MOUSE_DOWN, startDragging);
function startDragging(event:Event):void {
volume_mc.mySlider_mc.startDrag(false,rectangle);
dragging = true;
volume_mc.mySlider_mc.addEventListener(Event.ENTER_FRAME, adjustVolume);
}
function adjustVolume(event:Event):void {
var myVol:Number = volume_mc.mySlider_mc.x / 100;
var mySoundTransform:SoundTransform = new SoundTransform(myVol);
if (mySoundChannel != null) {
mySoundChannel.soundTransform = mySoundTransform;
}
}
stage.addEventListener(MouseEvent.MOUSE_UP, stopDragging);
function stopDragging(event:Event):void {
if (dragging) {
dragging = false;
volume_mc.mySlider_mc.stopDrag();
}
}
Syntax errors are just what it says they are, the code is not properly written. For instance , you shouldn't have an underscore after URLREquest
var musicPiece:Sound =
new Sound(new URLRequest("http://blog.0tutor.com/JeffWofford_Trouble.mp3"));
to start at the same place should be commented out, simply because it's a comment, it's not a variable or a function.
to call a function "play_" is not really good practice either. Call it soundPlay, if you're concern about conflicts.
same comment for pause_ and stop_