I have a Moto Mc9096 device, EDMK SDK, VS2008 etc all of the prereq's
I'm having an issue where once I've scanned a barcode it constantly repeats the event. normally when this happens its a flag or status needs changing but there are no obvious settings to stop it reading again.
code below
private void Barcode_Read(object sender, ReaderData readerdata)
{
if (readerdata.Text != null)
{
if (readerdata.Text == "abc")
{
MessageBox.Show(readerdata.text);
}
}
}
Notes
I've tried
bar.Dispose();
bar.Reader.Actions.Flush();
bar.ReaderData.Dispose() ;
with no success. the EnabledScanner is set on form load and off during form close.
My expectation was when the user scans a barcode it fires the read event once.
but it constantly fires after the users first scan.
You might want to check the aimType property, by default it should be AIM_TYPE_TRIGGER but other settings allow a single trigger pull to perform multiple scans (AIM_TYPE_CONTINUOUS_READ) so perhaps that has been changed.
You should have some samples installed by the SDK at file:///C:/Users/Public/Motorola%20EMDK%20for%20.NET/v2.9/SampLauncher2008.htm (by default) that show best practice.
Related
The addition of ServerValue.increment() (Add increment() for atomic field value increments #2437) was a great news as it allows field values to be increased atomically in Firebase RTDB.
I have an application that keeps inventories and this function has been key because it allows updating the inventory regardless of whether the user is offline at times. However, I started to notice that sometimes the function is executed twice, which completely misstates the inventory in the wrong way.
To isolate the problem I decided to do the following test, which shows that ServerValue.Increment() works wrong when the connection goes from Online to Offline:
Make a for loop function from 1 to 200:
for (var i = 1; i <= 200; i++) {
testBloc.incrementTest(i);
print('Pos: $i');
}
The function incrementTest(i) must increment two variables: position (count from 1 in 1 up to 200) and sum (add 1 + 2 + 3, ..., + 200 which should result in 20,100)
Future<bool> incrementTest(int value) async {
try {
db.child('test/position')
.set(ServerValue.increment(1));
db.child('test/sum')
.set(ServerValue.increment(value));
} catch (e) {
print(e);
}
return true;
}
Note that db refers to the Firebase instance (FirebaseDatabase.instance.reference())
With this, comes the tests:
Test 1: 100% Online. PASSED
The function works properly, reaching the two variables to the correct result (in the Firebase console):
position: 200
sum: 20100
Test 2: 100% Offline. PASSED
To do this I used a physical device in airplane mode, then I executed the for loop function, and when the function finished executing I deactivated airplane mode and checked the result in the firebase console, which was satisfactory:
position: 200
sum: 20100
Test 3: Start Online and then go to Offline. FAILED
It is a typical operating scenario when the Internet Connection goes down. Even worse when the connections are intermittent, you are traveling on a subway or you are in a low coverage site for which Offline Persistence is a desired feature. To simulate it, what I did was run the for loop function in online mode, and before it finished, I put the physical device in airplane mode. Later I went Online to finish the test and see the results on the Firebase console. The results obtained are incorrect in all cases. Here are some of the results:
As you can see, the Increment was erroneously repeated 10, 18 and 9 times more.
How can I avoid this behavior?
Is there any other way to increment atomically a number in Firebase that works properly online / Offline ?
firebaser here
That's an interesting edge-case in the increment behavior. Between the client and the server neither can be certain whether the increment was executed or not, so it ends up being retried from the client upon the reconnect. This problem can only occur with the increment operation as far as I can tell, as all the other write operations are idempotent except for transactions, but those don't work while offline.
It is possible to ensure each increment happens only once, but it'll take some work:
First, add a nonce to write operation that unique identifies this operation. You can use a push key for this, but any other UUID also works fine. Combine this with your original set() call into a single multi-path update call, writing the nonce to a top-level node with a server-side timestamp as its value.
Now in your security rules for the top-level location, only allow the write if there is no existing data. This ensures the secondary writes you're seeing get rejected, and since security rules are checked across multi-path updates as a whole, the faulty increment will get rejected too.
You'll probably want to periodically clean up the node with nonce keys, based on the timestamp value in there. It won't matter for performance (since you're never searching here outside of during the cleanup), but may help control the storage cost for the nonces.
I haven't used this approach for this specific use-case yet, but have done it for others. If you'd include a client-side retry, the above essentially builds your own multi-path transaction mechanism, which is what I needed it for in the past. But since you don't need that here, it's simpler without that.
Based on #puf answer, you can proceed as follows:
Future<bool> incrementTest(int value, int dateOfToday) async {
var id = db.push().key;
Map<String, dynamic> _updates = {
'test/position': ServerValue.increment(1),
'test/sum': ServerValue.increment(value),
'test/nonce/$id': dateOfToday,
};
db.child('previousPath').update(_updates)
.catchError((error) => print('Increment Duplication Rejected ${error.message}'));
return true;
}
Then, in Firebase Security Rules, you need to add a rule in test/nonce/id location. Something as follows:
{
"previousPath": {
"test": {
".read": "auth != null", //It depends on your root rules
".write": "auth != null", //It depends on your root rules
"nonce": {
"$nonce_id": {
".validate": "!data.exists()" //THE MAGIC IS HERE
}
}
}
}
}
In this way, when the device tries to write to the database again (wrongly), Firebase will reject it since it already had a write with that same ID before.
I hope it serves someone else!!!
I want to show a text for the first time running like "Hi, my name is NAVI." and then when the player will start the game again the next time it will another text for example "Welcome back."
Using player prefs is probably the easiest solution, though definitely not the only one*.
Due to the lack of boolean playerpref I usually opt to use SetInt/GetInt instead, but that's personal preference. You could also do it with a string or float.
private void Start()
{
if(PlayerPrefs.GetInt("HasLaunched", 0) == 0)//Game hasn't launched before. 0 is the default value if the player pref doesn't exist yet.
{
//Code to display your first time text
}
else
{
//Code to show the returning user's text.
}
PlayerPrefs.SetInt("HasLaunched", 1); //Set to 1, so we know the user has been here before
}
Playerpref stores values between sessions, so the next session will still have "HasLaunched" set to 1. This is however stored on the local device. so users can manually reset it if they'd really want to.
If you ever want to show the "first launch" text again, simply set HasLaunched back to zero, or delete it altogether with DeleteKey("HasLaunched");
*There are plenty of alternative solutions, like storing it in a config file locally, or using a remote database (this would be required if you don't want users to be able to reset it). They would however come down to the same principle. Setting a value to true or 1 somewhere, and checking that value on launch.
If I have two different VSTO AddIns installed on the same Word application, is there a way to know which one of them first receives the events raised by Word. For example the DocumentOpen event?
Can I control that order?
Thanks
I didn't find anything specific about event order in multiple add-ins (but I believe I've read something about it years ago) so I did simple test
I created three Excel add-ins with this code
private void ThisAddIn_Startup(object sender, System.EventArgs e)
{
this.Application.WorkbookBeforeSave += Application_WorkbookBeforeSave;
}
void Application_WorkbookBeforeSave(Excel.Workbook Wb, bool SaveAsUI, ref bool Cancel)
{
System.Windows.Forms.MessageBox.Show("Add-in 1");
}
One of them I gave it random name as I wanted to know if Excel runs them in alphabetical order, in one of the add-in I set the Cancel = true
I don't know why but Excel always fired the ExcelAddin 2 first, then ExcelAddin 1 and finished with AAExcelAddin. I tried to rebuild (I also cleaned my solutions first) in different order but the order was still the same (note the very first addin created was the ExcelAddin 1) No matter if I run it from VS or just simply start Excel and pressed CTRL+S
Based on above I would say that you should not have any logic in your code that assume certain order of add-ins. You never know if any new add-in will break the order.
Also keep in mind that if you use any of the cancellation events (has the argument Cancel) and you cancel it (Cancel=true) then all the other add-ins will receive the event and will still run it but the Cancel flag will be set to true from the previous one.
In my case I set Cancel=true in the add-in that was fired at first (ExcelAddin 2) and even the two other add-ins received the event, they didn't save as saving was cancelled in the first one.
In my application I need to wait until external program (using QProcess) is finished. I want to keep the application responsible so blocking methods are unacceptable.
Also I need to disallow user input. I've tried to make QEventLoop and exec it with QEventLoop::ExcludeUserInputEvents flag, but as documentation says it only delays an event handling:
the events are not discarded; they will be delivered the next time processEvents() is called without the ExcludeUserInputEvents flag.
So I implemented simple event filter and install it on qApp (the idea is took from Qt Application: Simulating modal behaviour (enable/disable user input)). It works well, but sometimes QApplication::processEvents function never returns even if I specify the maximum timeout. Could anyone help me to understand for what reasons it periodically happens?
class UserInputEater : public QObject
{
public:
bool eventFilter(QObject *object, QEvent *event)
{
switch(event->type())
{
case QEvent::UpdateRequest:
case QEvent::UpdateLater:
case QEvent::Paint:
return QObject::eventFilter(object, event);
default:
return true;
}
}
};
-
UserInputEater eventEater;
qApp->installEventFilter(&eventEater);
QProcess prc;
prc.start("...");
while(!prc.waitForFinished(10))
{
if(qApp->hasPendingEvents())
{
// Sometimes it never returns from processEvents
qApp->processEvents(QEventLoop::AllEvents, 100);
}
}
qApp->removeEventFilter(&eventEater);
UPD: Seems like it depends of the timeout value for QProcess::waitForFinished.
I guess you are filtering some useful events (for example, QEvent::SockAct could be involved). Try to add some debug output and find out which event types you're actually filtering. Or it might be better to specify the black list of events you want to block instead of white list of events you want to allow. See this answer.
Also you shouldn't use return QObject::eventFilter(object, event);. You should use return false. All other event filters will be called automatically.
This solution however seems weird and unreasonable to me because you can just call setEnabled(false) for your top level widget to block user input, and then you can use QApplication::processEvents without any flags.
I am trying to register to a "Device added/ Device removed" event using WMI. When I say device - I mean something in the lines of a Disk-On-Key or any other device that has files on it which I can access...
I am registering to the event, and the event is raised, but the EventType propery is different from the one I am expecting to see.
The documentation (MSDN) states : 1- config change, 2- Device added, 3-Device removed 4- Docking. For some reason I always get a value of 1.
Any ideas ?
Here's sample code :
public class WMIReceiveEvent
{
public WMIReceiveEvent()
{
try
{
WqlEventQuery query = new WqlEventQuery(
"SELECT * FROM Win32_DeviceChangeEvent");
ManagementEventWatcher watcher = new ManagementEventWatcher(query);
Console.WriteLine("Waiting for an event...");
watcher.EventArrived +=
new EventArrivedEventHandler(
HandleEvent);
// Start listening for events
watcher.Start();
// Do something while waiting for events
System.Threading.Thread.Sleep(10000);
// Stop listening for events
watcher.Stop();
return;
}
catch(ManagementException err)
{
MessageBox.Show("An error occurred while trying to receive an event: " + err.Message);
}
}
private void HandleEvent(object sender,
EventArrivedEventArgs e)
{
Console.WriteLine(e.NewEvent.GetPropertyValue["EventType"]);
}
public static void Main()
{
WMIReceiveEvent receiveEvent = new WMIReceiveEvent();
return;
}
}
Well, I couldn't find the code. Tried on my old RAC account, nothing. Nothing in my old backups. Go figure. But I tried to work out how I did it, and I think this is the correct sequence (I based a lot of it on this article):
Get all drive letters and cache
them.
Wait for the WM_DEVICECHANGE
message, and start a timer with a
timeout of 1 second (this is done to
avoid a lot of spurious
WM_DEVICECHANGE messages that start
as start as soon as you insert the
USB key/other device and only end
when the drive is "settled").
Compare the drive letters with the
old cache and detect the new ones.
Get device information for those.
I know there are other methods, but that proved to be the only one that would work consistently in different versions of windows, and we needed that as my client used the ActiveX control on a webpage that uploaded images from any kind of device you inserted (I think they produced some kind of printing kiosk).
Oh! Yup, I've been through that, but using the raw Windows API calls some time ago, while developing an ActiveX control that detected the insertion of any kind of media. I'll try to unearth the code from my backups and see if I can tell you how I solved it. I'll subscribe to the RSS just in case somebody gets there first.
Well,
u can try win32_logical disk class and bind it to the __Instancecreationevent.
You can easily get the required info
I tried this on my system and I eventually get the right code. It just takes a while. I get a dozen or so events, and one of them is the device connect code.