I have a win 7 application in vb.net for scanner data collection, the app first shows the main form -- top level, this form contains a lot of buttons, click any button will go to second level forms, based on scanned data input, the 3 level forms can show from a point of second level form(second level form not closed at this point), close the 3rd level form, you can go back to second level form at the point it is out for 3rd level form and continue to run rest program in send level form, close second lever form you can go back to main form to click another button to go. Main form just call the scanner class to initial, it will not handle the scanner event. the 2nd and 3rd level form load has the addhandler statement. No matter which form is on top will handle the scanner event to process scanned data in that particular form, every form process that data differently.
In order to keep the scanner event for every available form, I put the event in a module, and when the scanner class read a data will raise this event. when I test it, whatever the first available form handle the data well, and when the forms switch back and forth, the event handler not work any more, and program freeze or stop working. I cannot figure out why. I hope you guys can give me some advise about what is better way to handle this kind of event.
Thanks!
In a form, include a handler to call your function in the module. When the form is no longer active, unload the form or remove the scanner handler. If there are two active handlers for an event, it can cause problems.
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I am currently working on a LabVIEW project and have found myself stuck on how to make a while loop exit when I press the abort (stop) button. For a simple while loop I understand how to do this - but the problem is that this while loop is nested inside of an event structure and I'm guessing that the button cannot be pressed while the loop is executing. Attached here is a picture of part of my code (that contains this specific event case which is causing me problems): To spend a little more time explaining what the problem is - I think the code is doing what I want it to do (namely output a set of commands in a repeated cycle with a wait timer) but I cannot stop the code mid cycle (pressing the abort button with my mouse does nothing - as in the button doesn't show it being pressed and the indicator shows no change, I also can't use any other functionality of my program during the cycle which I'm assuming is related). And I do not want to stop the LabVIEW program from running entirely - just the code inside the while loop pictured above. This is what the front panel is configured too for completeness:
Essentially what I want to happen is the while loop to execute when I press DWG and in the middle of the cycle be able to abort it. Sorry if my code seems a little messy. Additionally, I've tried the same code with a for loop originally (via a conditional terminal so it could stop early) and that didn't work either. Thanks for any help I appreciate it!
Your problem is that inside the event structure, by default the UI is frozen so no UI actions (keyboard/mouse/etc) are processed until you exit that frame.
Option 1. You can right click the Event Structure and select "Edit events handled by this case" dialog and then uncheck the "Lock panel" checkbox -- that will allow the UI to be live while you are in that frame. I do not recommend this solution generally unless you have an extremely simple user interface because it leads to the user being able to change controls without the events behind those controls being processed (not a good UI experience for users). But if the UI is simple enough, that works.
Option 2. You can create a user event that is the code you want inside your While Loop. When the Deg Wait Go button is pressed, use the "Generate User Event" node to trigger that event. Do the same thing in the user event case so that the event re-triggers itself if and only if the Abort button has not been pressed.
Option 3. Create a separate loop OUTSIDE your UI loop that does your processing with some sort of command queue running between the UI loop and that other loop. The other loop moves into various states at the request of the UI loop... it's the one that does nothing until it receives a "go" message and then keeps looping until it receives a "stop" message. You can Google "queued message handler" for extensive details of this solution. This is the most common solution for complex UI requirements, especially useful for separating concerns of the UI code from the execution code.
We have a huge application that runs through a mass of code for every click you do. In one specific case, where you have a specific control in plain sight (so that the events are firing) and you load some special data into it and then click on the new button the form loses some events, like the closing event (you cannot close the form anymore and stop points in debug mode are not triggered) and one validating of a ComboBox that is really needed for the program. The only thing you can do when you get this kind of error is to restart the application to get out of this subform. But I tested it for 2 days now and even when I activate all points in the 'Exception Settings' I don't get any exceptions. The form (and other controls) are not losing ALL events. The resize, for example, still works. Even a specifically called AddHandler is not firing. Can you iterate somehow through the EventHandlerList? Or is there any way to test WHERE the event dies? Somehow any ideas on how to debug such a problem?
I have my form with a menu bar and space underneath to display my controls. One of the buttons in my menu bar is suppose to be a print button that prints a graph that's currently in a User Control I display in the form. If the graph was on the form in the print button's eventhandler I could just simply call
graph.printing.print(true)
which isn't going to work in my case since the graph is in the control and not the form.
How do I communicate with a User Control from the containing form and access or pass its variables when needed? I also have a status bar on the bottom of the form which would also need to get updated from the User Control, but I'll be able to deal with that if I got help with just this one part. Please bear in mind, I also have another User Control I'm going to add to the form which will also contain a graph which will need the same treatment as the other graph on the first control when the print button is pressed. I plan on swapping these two out so I have one form displaying one control at a time.
I got this idea from this answer: https://stackoverflow.com/a/18191630/2567273 but after further research I can't find anyone asking about the actual communication process between a form and the control it contains.
I think this answer is close to what I'm looking for, but I think it's leading me down the path to using panels instead of User Controls.
After typing this I noticed the closest answer to my question may be this, but that question has the child raising events and the parent responding while I have the parent raising the event and the parent has to get information from the child.
One way to think about this is Roles. Presumably you built this UserControl to handle the management of the data related to the graphs. As such you can think of them in the Role of a Graphs Specialist . Once you do that, printing them is actually just one more thing it should perhaps do.
The form on the other hand, is not special just because it happens to get receive the command from the user to print. Its role in this might simply to be to know which usercontrol to contact and which method to invoke:
Sub PrintGraphMenuClick....
Select Case something ' determinant as to which UC to contact
Case operation.Foo
ucFoo.PrintGraph
Case operation.Bar
ucBar.PrintGraph
Other menu options like Clear, NewGraph, Save and whatever else there is somewhat the same way. The Form's Role here may be to receive the command from the user and pass it along to the right control, invoking the correct right method and passing the correct parameters - that is not a trivial task.
Of course, rather than a MainMenu, the usercontols could alternatively implement a ContextMenu and even receive those commands directly.
Very often offloading an operation to something else results in so many properties, filenames, streams etc having to be moved from here to there that it becomes burdensome. In this case it is not like the MainForm has some special ability regarding printers that the UserControl cannot handle.
There is only one right solution:
1) Add an event to your user control.
2) Raise the event when the particular "thing" happens in the user control.
3) Attach a handler to the event in Form code.
4) Add code to update the bottom bar in the event handler.
I have a form in a vb.net windows form application called PolicyRefreshStatus.vb that has a ProgressBar control on it. From the main form called EditPolicy.vb I need to show PolicyRefreshStatus.vb over top of EditPolicy.vb - but the way things are wired I'm controlling the the ProgressBar and it's steps from logic inside EditPolicy.vb.
If I display the PolicyRefreshStatus.vb bar using the .show() method things work fine. The problem is if the user clicks back on the main form then PolicyRefreshStatus.vb losses focus. If I show PolicyRefreshStatus.vb as a modal form using .ShowDialog() then execution halts in EditPolicy.vb after the .ShowDialog() statement.
so for example in the code:
mPolicyRefreshStatus = New PolicyRefreshStatus
mPolicyRefreshStatus.pbMax = mPolicy.ClaimsUpdateMax
mPolicyRefreshStatus.ShowDialog()
mPolicy.UpdateFromFIS()
The line mPolicy.UpdateFromFIS() never executes because it's waiting for the PolicyRefreshStatus form to close.
How can I show PolicyRefreshStatus in a modal form but let execution continue in EditPolicy.vb?
You've got a couple of related options.
This first is to pass the unit of work to the progress bar in the form of a delegate or a class implementing an Interface. Something like this (not checked for correctness, just a rough example):
mPolicyRefreshStatus = New PolicyRefreshStatus
mPolicyRefreshStatus.pbMax = mPolicy.ClaimsUpdateMax
mPolicyRefreshStatus.UnitOfWork = AddressOf(mPolicy.UpdateFromFIS())
mPolicyRefreshStatus.ShowDialog()
Then within the progress form you can call back to the routine that actually does the work.
Another approach is to define events on your ProgressForm and then the owning/launching object can handle those events to do the work in. With this option you can create a fairly detailed set of events to be able to handle incremental work or cancels, but the concept is the same, youu are calling back from the progress form into launcher to perform the actual business logic.
You cannot show the form modally and let your routine continue. You must show the form Non-modally and then do your other stuff, closing the form when you've finished. Maybe a loop until the task has finished?
Using Show() with a parent form parameter will give you better usability. More like a tool window.
I have a form in a Pocket PC app that is set to be the Application form using:
Application.Run(New frmMain())
Somehow this form is getting closed for no reason while working on another form. No closing event is fired and nowhere in my code can you close the main form anyway. It is only closed by clicking the OK button at the top right of the window. When this is clicked, the user is prompted if he/she really wants to close the application. However, this is not occurring either.
Basically, I am on another form which adds a new record to the database. After adding the record the gotFocus event is somehow called for frmMain. When the code in the gotFocus event reaches a reference to a control on the form, there is an exception that states that the object is disposed.
When I bypass the code in the gotFocus event, the application just closes completely. I verify this by checking that it is not running in the device's memory.
I have been stepping through code for 2 hours and I have absolutely no idea why this could be occurring. Anyone possibly have a tip?
This sounds as an exception being raised anywhere. Maybe an exception on another thread? Look at the output window to see what it says.