In the Azure Hub device twin we have Desired Properties and Reported Properties. I guess that is like a setpoint and actual value.
So when I want to change a value I update the Desired Property and then wait for the corresponding Reported property to be updated with the actual value would that be right?
When updating the Desired Property, is it normal practise to not touch the corresponding Reported Property? I mean set it to null or something to indicate that we do not have an actual reported value yet... If the device property was indeed updated but the the report message from the device fails to arrive we will have an old reported value. I would think it should not be updated and maybe there are timestamps for these properties to see if the reported value is not yet updated.
It's not normal practice to change the reported properties of a device when changing the desired property. If the device has not reported that property, it simply won't be available in the reported properties. So to answer both of your questions, here's a scenario:
Your device is running, having a great time. It has received no desired properties and has reported no properties of its own.
You go to the portal and add a desired property, the property foo with a value of bar, you change nothing else.
The device receives the request for this property, implements the change and reports to the IoT Hub that foo is now bar.
Looking at the device twin in the portal, you notice a reported property, also the metadata for the reported properties indicates a $lastUpdated value with a timestamp.
Reported properties are just that, reported. A device can report properties that aren't in the desired properties, or update a reported property without receiving a new desired property.
Related
I am investigating a use case where ignite has to listen to changes of a property of an object in the data grid and do some operations on that object. For performance, I want the processing to be done on the same node where the data is.
How can I get an event when the property of a object has changed to a specific value (eg. Object 'X' has a property 'state' which is set to 'scheduled' from 'created') and make sure that only events are taken from the node where the object lives in?
How can I make sure that when I got the event and start processing it, nobody else changes the object (only read is allowed) until processing is finished (in other words, a transaction starts as soon as the event is picked up)?
How can I make sure that the processing code is deployed to all nodes (processing is stateless) and that it only operates on local data (without having a hard link between data object and code, in other words, if the processing code is updated in the future, the objects stay untouched)
What I got from the docs is the following:
// Local listener that listenes to local events.
IgnitePredicate<CacheEvent> locLsnr = evt -> {
// CODE
return result;
};
// Subscribe to specified cache events occuring on local node.
ignite.events().localListen(locLsnr,
EventType.EVT_CACHE_OBJECT_PUT);
In the CODE block; I have to check for a state change on 'evt.newValue()', can't that be done earlier? Ie. as a paremeter to localListen somehow?
In the CODE block, is the Object locked until I return the result? In other words, is it in here that I am sure nobody can changes the object and that I can safely change my Object? IMO it is a strange place to do that in a 'Predicate' definition and not in a handler class.
Sven
Sven,
Your code looks correct and should work as you expect. Answering your questions:
Event listener is called right after the value is updated, so I think it's OK to check the field you're interested in inside the listener. If the field is not changed, just return right away.
The object is locked, because listener is called inside the sync block for the entry. You can modify the same object, but I would not recommend to execute any sync operations like cache updates inside the listener because it's error-prone and can affect performance. You should do this asynchronously, so that the lock is released as soon as possible.
So, I asked another question here:
How to tell the difference between a user-tapped keyboard event and a generated one?
One of the answers that came up was to use the "mouse pressure" field (unlikely to be used for a keyboard event) to mark the event as needed.
So, I'm trying:
CGEventSetIntegerValueField(myKeyboardEvent,
kCGMouseEventPressure,
0xFEEDFACE);
The problem is:
I don't know what 0xFEEDFACE means. What does that value default to? What should I set it to? How can I check whether it has been marked by me?
Running the above code gives me an error:
<Error>: kCGErrorIllegalArgument: CGEventSetIntegerValueField: invalid event
0xFEEDFACE is just a dummy value. It's one of a number of 4-byte numbers with silly hex spellings that will stand out when you're looking at memory.
The function takes three arguments: an event, a CGEventField (which is an enum), and an int64_t (8-byte signed integer) whose range of valid values probably depends on the field. I used 0xFEEDFACE to indicate that you could try putting an arbitrary "magic" value in there,* and then check for it when you received the event, using CGEventGetIntegerValueField. If your event tap receives a new event that has your "magic number", then it was (almost certainly) sent by you. Otherwise, it was sent by the system.
To sum up and answer your explicit questions: that argument doesn't default to anything; you should pass something arbitrary that is unlikely to be used by the events system (you might want to inspect a series of events sent by the system to see what "real" values look like); the idea is that your arbitrary value allows you to check that the event was marked by you.
As for the error, it looks like I was wrong. I thought that you might be able to set any field on any kind of event (e.g., using the "mouse pressure" field on a keyboard event, since the system almost certainly won't have set that) to pass along arbitrary information (and so identify the events that you've constructed yourself). It seems, however, that Event Services won't let you do that. There may be other fields that you can use, but I don't know for sure.
*I assumed you would understand that it was a junk value; sorry.
I'm working on a web application that enables users to login, only at specific locations. I'm using CLLocationManager and I initialized and called startUpdatingLocation at AppDelegate -didFinishLaunchingWithOptions. My UIWebView is supposed to pull the location at initialization to determine whether user's within the specified locations. However, at the launch of my application, [locationManager location] is always null and updates after my UIWebView is initialized and displayed therefore already sending an error message to the user.
How do I make my locationManager update its location at initialization?
Sounds like you've coded the location stuff correctly. What you are missing (but have seen) is that the update most certainly does not happen instantaneously. You need to "gate" the rest of your UI's presentation (i.e. your webview) on the location information becoming available. There are a lot of ways to do this. A common tactic is to present a full-screen "HUD" or veil with some indicator to the user that the app is initializing or locating them (with an activity indicator, too, is always a nice touch.) Behind that (out of sight to the user) you can be waiting for the location result and then kickoff the appropriate UI update, and then drop the veil.
Any of that make sense or give you some ideas? I've done this plenty of times. Synchronizing async activities (like location updates) with real-time UI updates that make sense can be challenging, but isn't impossible. :-)
You will need to account for an initial nil value in your applications UI and wait for the first location update.
-location
Discussion
The value of this property is nil if no location data has
ever been retrieved.
It is a good idea to check the timestamp of the location that is
returned. If the receiver is currently gathering location data, but
the minimum distance filter is large, the returned location might be
relatively old. If it is, you can stop the receiver and start it again
to force an update
Also you should check out Region Monitoring since you would like for you users to only be able to login at specific locations.
My scenario is the following:
I have a workflow (lets call it customActivity1) that do the basic actions for my system. I also have another workflow (customActivity2) that uses customActivity1 and do higher level actions. When I call customActivity1, I must pass on a few parameters, like Boolean or String values. I want to show some of these parameters as a checkbox or combobox (so the developer of customActivity2 can pass on only valid values) and found out that I can do that by setting the argument as PROPERTY (instead of In).
By doing a research, I also found out that you can’t directly use this argument in expressions, so I keep getting errors on my customActivity1.
That said and knowing that I need to narrow what the designer can pass on, how could I do that without using an activity designer or where could I find an answer?
I also attached two pictures, one of what I need and the other of the error I’m getting.
Thanks in advance.
The reason an InArgument only shows you a text field instead of a checkbox is because they are expressions not literal values. There is still type checking though, if you enter the value 1 you get the error message that an integer cannot be converted into a boolean.
You cannot do this. You can only bind to InArguments.
If you bind an InArgument and look at the xaml, you'll see something like this:
<p1:MyActivity MyInArgument="[BoundValue]" ...
The Workflow Runtime knows how to handle these. It doesn't know how to handle binding POCO properties.
If you want to model data flow but want to have a different user experience in the property grid I recommed using arguments (as they convey data flow semantics) and customizing the property grid for those arguments. There is a sample that demonstrates how to do this in the WF4 samples (sample readme available at http://msdn.microsoft.com/en-us/library/ee834515.aspx)
I have some trouble with a core data project. I have a NSArrayController with NSManagedObjects in it, and + / - buttons. If i delete a object in the row after the file has been saved it works perfectly, but if I add a new object, and immediately delete it again (without changing any of the default values), i get an error:
Serious application error. Exception was caught during Core Data change processing: Unknown number type or nil passed to arithmetic function expression. with userInfo (null)
Unknown number type or nil passed to arithmetic function expression.
It's the same case if i undo the add of the new object.
Anybody able to give me a pointer what to do? I assume it has something to do with that it only has an temporary ID, but how to solve it i don't know.
I found the problem and solution. For the record i will describe it.
The problem was that the object in its init function added an observer on itself. This was probably what triggered the error. If i before i delete the object remove itself as observer, the error is not produced.
Tables don't usually contain NSManagedObjects. Rather, either an NSArrayController is providing the managed objects' attributes as values via bindings or an object conforming NSTableViewDataSource is. The deletion of a selected object provided in either of these scenarios can be done a myriad of ways. The problem is, you haven't explained at all how your case is set up.
Is it possible your deletion (whatever target/action your button is wired to) is being passed nil or something unexpected? I can imagine a similarly-frighenting error if you asked a managed object context to delete a float value or some other random thing ...