First of all, sorry for the generic title, I didn't know who to write my question.
I'm in a trouble, i'm trying to create a control but I don't know how to do it. Here is what I would like to do:
I created a chronometer (just an int that increase 1 by 1) and I want to write that: If clickNumber == 1 and the chronometer is less than 144, wait until it reach this number, if it is 144, then make and action, then exactly the same, if clickNumber == 2 and the chronometer is less than 72, wait until it reach this number, if the chronometer is == 72 then make and action.
I think it might be so easy to do, but I can't see how to do it.
Thank you all
Your issue is better thought in terms of events and objects.
Let's say you have a Chronometer and it has at least three parts: Display, button and code. The display will show the value of the chronometer. The button will behave as you describe. The code is the part that manages everything.
Your chronometer code will be receiving events from at least two sources: Timer and Button. The timer is a system time that sends you message periodically (like once a second). The button will send your chronometer code an event when the user clicks on the button.
So you will need to have some static variables to hold your information.
You will need to think in terms of the event:
if event == button click
then increment click and check click count.
endif
if event == timer
then
increment chronometer value.
if chronometer value == limit, then stop the timer.
endif
The implementation of the algorithm depends on the GUI framework you are using.
Related
I have implemented a GUI and my problem is to handle two tasks at the same time. My code should be provide the opportunity to execute the task by clicking on a Pushbutton or by listening to CAN messages with the read function.
I had the idea to read CAN messages with a while loop until the pushbutton is clicked. Is this a good approach?
Your GUI itself should have some sort of main loop that continuously runs waiting for any updates to process. Each iteration of which, it should be reading the CAN messages and if there is a trigger for a specific task, you should have code implemented that handles that. The same thing goes for any of your push buttons. You should not have any logic that stops checking the CAN if a button is pushed, or vice-versa. Instead, you should keep track of specific events being triggered with a boolean and prevent retriggering them until they are complete/resolved.
I have a trackbar control in my app and I want to do something when user starts scroll operation (when he clicks on the trackbar's thumb). Since WM_HSCROLL doesn't notify about such event, I was wondering how do I get to know when user starts scrolling. I'd like to avoid processing SB_THUMBTRACK request since thay would mean I'd have to process it all the time when user's scrolling, and I just want to know when he starts doing it.
Just process TB_THUMBTRACK and ignore all subsequent TB_THUMBTRACKs until you get TB_ENDTRACK. That's roughly 5-9 lines of code.
For trackbars you also should use the TB_* (trackbar) constants and not the SB_* (scrollbar) constants even if their respective values are the same (e.g. SB_ENDSCROLL == TB_ENDTRACK == 8, SB_THUMBPOSITION == TB_THUMBPOSITION == 4).
Basically exactly what the title says. I would like to update the text that a button contains every 1 second when the user presses that particular button. I have noted that when the program doesn't have focus it works alright and the text refreshes correctly but when I am hovering over the program or when I am trying to click on it's menu Windows inform me that the program is unresponsive and asks me if I want it terminated. When the loop finishes the program returns to its normal state. Also any action I might have done (like moving it around or closing it) while it was Sleep()-ing is executed after the loop. Here is a bit of code:
case ID_BUTTON_START:
// Code executed when pressing Start Button.
char startButtonText[30]; // Storing next loop text
for (int i=5; i>0; i--)
{
sprintf(startButtonText, "Starting in ... %d", i);
SendMessage(hwndButtonStart, WM_SETTEXT, 0, (LPARAM)(startButtonText));
Sleep(1000);
}
Is this normal? If not what's causing this?
The WndProc does not process messages asynchronously within an application which means all messages are expected to be handled quickly and a return value delivered immediately. You must not Sleep in the UI thread since it will block other UI events from being processed. Any heavy work or synchronous requests/jobs which are likely to take a long time should be performed in worker threads. There are at least three viable options:
Create a new (worker thread) for the task.
If the task is likely to be done often, use a thread pool instead.
Set and subscribe to timer events.
I think the call to Sleep() might be keeping you from returning from the WndProc, so your application is not processing the incomming events for 5 secs. I suggest you try to subscribe to 5 timer events in 1s, 2s,..., 5s. Like when the timer message is recieved the button text must change. I don't know a way how to do that off the top of my head.
I am writing a qt program and have the following requirement.
When 30 sec passed without any click, lock the screen. If someone clicks again after these 30 secs, redirect him to a login screen.
I have read the qt doc about event and I believe that I need either method 1 or 2 to process mouse event.
1.Installing an event filter on qApp
An event filter on qApp monitors all events sent to all objects in the application.
2.Reimplementing QApplication::notify().
Qt's event loop and sendEvent() call this function to dispatch events. By reimplementing it, you get to see events before anybody else.
They also seems powerful to me, but I don't understand their difference.
Which one suits my requirement? Thank You.
You can basically achieve the same thing with either solution except for the fact that QApplication::notify (or its override) will be called before any event filter that may be on your application.
As the first approach does not require subclassing QApplication, it usually is the preferred one.The only reason to override QApplication::notify in your case would be if you needed to override it due to other reasons anyway, e.g. because you need to do anything related to your own custom events.
But looking at your requirements I would personally go for the following solution:
Install an event filter on qApp
Create a timer with a 30 seconds interval
Connect the timer to the lock screen method
Have your event filter reset the timer every time a mouse press is detected.
Dependent on your application you might also want to look for KeyPress events and maybe MouseMove events as well.
I have a QAbstractItemView that needs to react to single and double click events. The actions are different depending on whether it was single clicked or double clicked. The problem that is occurring is that the single click event is received prior to the double click event.
Is there a recommended way/best practice for distinguishing between the two? I don't want to perform the single click action when the user has actually double clicked.
I am using Qt 4.6
It's a good UI design to make sure your single-clicks and double-clicks are conceptually related:
Single-Click: select icon
Double-Click: select icon and open it
Single-Click: select color
Double-Click: select color and open palette editor
Notice how in these examples the single-click action is actually a subset of the double-click. This means you can go ahead and do your single-click action normally and just do the additional action if the double-click comes in.
If your user interface does something like:
Single-Click: select icon
Double-Click: close window
Then you are setting your users up to fail. Even if they remember what single-clicking does versus double-clicking all the time, it's very easy to accidentally move your mouse too far while double-clicking or wait too long.
Edit:
I'm sorry to hear that.
In that case, I found these two articles useful:
Logical consequences of the way
Windows converts single-clicks into
double-clicks
Implementing
higher-order clicks
You can find answer in the thread titled Double Click Capturing on QtCentre forum;
You could have a timer. Start the
timer in the releaseEvent handler and
make sure the timeout is long enough
to handle the double click first.
Then, in the double click event
handler you can stop the timer and
prevent it from firing. If a double
click handler is not triggered, the
timer will timeout and call a slot of
your choice, where you can handle the
single click. This is of course a
nasty hack, but has a chance to work.
wysota
Using PySide which is the Python binding of Qt 4.8 I saw that single clicks deliver a QEvent.MouseButtonPress event and double clicks deliver a single QEvent.MouseButtonPress event closely followed by a QEvent.MouseButtonDblClick. The delay is approximately about 100ms on Windows. That means you still have a problem if you need to differentiate between single and double clicks.
The solution needs another QTimer with a slightly higher delay than the inbuilt delay (adding some overhead). If you observe a QEvent.MouseButtonPress event you start your own timer, in case of timeout it is a single click. In case of a QEvent.MouseButtonDblClick it is a double click and you stop the timer to avoid counting as single click.