I am facing a problem regarding Signals and Slots mechanism of Qt. The core of the problem is here :
My application consists of 2 classes:
MainGUI : this class has all the core functionality of the app, and has some variables which store values relevant to the app.
Preferences : This class is used to draw and show a Settings panel, and has line-edit fields for updating the variables in MainGUI (using Signal-Slot mechanism)
Currently, i have connected them as follows:
Preferences *Pref;
MainGUI *M;
.
.
.
connect(Pref, SIGNAL(pref_varAChanged(QString)), M, SLOT(setVarA(QString)));
connect(Pref, SIGNAL(pref_varBChanged(QString)), M, SLOT(setVarB(QString)));
connect(Pref, SIGNAL(pref_varCChanged(QString)), M, SLOT(setVarC(QString)));
.
.
.
But, what this part does is that AS SOON AS the values are changed, the variables are updated, even though i have not click on 'APPLY' button (or an equivalent ACCEPT button...)
Please help me in implementing this functionality that the values A,B,C get updated only when a button, say, btn_accept is clicked...
PS : I know this seems a very easy problem, and should be only a few lines long, but i've been trying to solve it and have been hitting the wall every time. I'd appreciate if someone could point me in the right direction
Well, it seems i have figured out the problem.
It was simply a matter of emitting the 'variableChanged' signals when the ACCEPT button was clicked. This would update the variables in the MainGUI class.
It seems I had found the solution (read my comment), but I had misread the output my program gave, thus I had not realized that I had solved the problem until much later.
Thank you all for your comments. I'm sorry that this turned out to be such a waste of time.
Regards,
Harsh
Related
I have a program that will act as a network-linked visualizer for a hardware system with no screen (think RaspberryPi). I currently have a QTabWidget with around 45-50 QPushButtons and textboxes (for numbers), but I'm bothered by the amount of connect statements I'll have to make. Is there a better way to make this many buttons? I've seen methods for using an array, but nothing with using a QTabWidget and the only thing I saw on that was creating a form.
I'm sorry I can't give you a proper answer with code. I have no proper internet so I have to do this on a phone.
Set up an array of buttons, maybe even a custom class derived from QPushButton with a signal that includes an identifier for the button, such as std::string name. You can then run a loop assigning your connects with something like:
connect(buttonArray[x], SIGNAL(buttonIsPushed(std::string) ), receivingObject, SLOT(buttonWasPushed(std::string)))
Of course this may be of little help if the receiving object has to pass on the signal as a signal.
I've searched this extensively, and the answer I came up with about 20 times is to use CWnd::EnableWindow(FALSE). Currently, I have:
GetDlgItem(myComboBox)->EnableWindow(FALSE);
Instead of disabling the ComboBox, now the entire Dialog doesn't show up, and since it's a modal dialog (or at least I'm guessing that's the reason), the entire program gets locked up because I can't close the dialog if it's not there.
Is there a way to disable editing to this box without making it disappear entirely; similar to what SetReadOnly() does for a CEdit?
Edit:
Suddenly, the syntax above started working the next morning. I'm still not entirely sure why it didn't work in the first place.
EnableWindow(FALSE) is the correct function to call but your syntax looks like it may be incorrect (but it's hard to say with such a minimal example).
Is myComboBox an instance of CComboBox? If so, I'd expect to see:
myComboBox.EnableWindow(FALSE);
or, using the associated resource ID:
((CComboBox*)GetDlgItem(IDC_MY_COMBO_BOX))->EnableWindow(FALSE);
Threading issues or duplicate resource ID's can also cause weird issues.
It seems you are trying to call EnableWindow() from a different thread than the dialog's
You could try this, and see if it works for you:
GetDlgItem(myComboBox)->PostMessage(WM_ENABLE, (WPARAM)FALSE);
I was playing around with the Qt demo browser example mentioned here and noticed an anomaly when I tried making a minor change to the bookmark handling code.
My intention was to make the bookmarks in the toolbar open up in a new tab instead of the existing tab. It works perfectly for the bookmarks that are located directly on the bookmarks tab. But the bookmarks inside a folder are the ones which are behaving weirdly.
I modified the BookmarksToolBar::activated SLOT in the bookmarks.cpp to open the url in a new tab instead of existing tab. That's when I noticed that the SLOT is being called multiple times, the count being equal to the number of times the menu is rendered. i.e, the first time a menu item is activated, the SLOT is called once, the next time an item is activated, the SLOT gets called twice and so on.
I thought there must have been multiple signal-slot connections and thus I checked on the BookmarksToolBar::build() method where the signal-slot connection is done and found that the control flow enters the method only once. I am finding it hard to figure out how the SLOT is being called multiple times.
The project is question is an example project 'Tab browser' which comes with Qt and can be accessed by clicking on 'Examples' on the Qt-Creator welcome screen. Thus I did not post any source code here.
Any guidance or help in understanding the cause for this anomaly and possible solutions to fix it would be appreciated.
Found the cause of the problem and solution myself. The root of the problem is in modelmenu.cpp.
Apparently the ModelMenu::createMenu method connects the QMenu::triggered and QMenu::hovered signals to SLOT each time the method is called. The SLOT triggered emits the signal ModelMenu::activated.
Using Qt::UniqueConnection should solve the issue.
Replacing this:
connect(menu, SIGNAL(triggered(QAction*)), this, SLOT(triggered(QAction*)));
connect(menu, SIGNAL(hovered(QAction*)), this, SLOT(hovered(QAction*)));
With this:
connect(menu, SIGNAL(triggered(QAction*)), this, SLOT(triggered(QAction*)),Qt::UniqueConnection);
connect(menu, SIGNAL(hovered(QAction*)), this, SLOT(hovered(QAction*)),Qt::UniqueConnection);
Fixed the problem. Just leaving this here hoping this would help someone in future.
I'm working on a credential provider for windows 7 with cpp. I want to disable textboxes and submit button while the system is working in the background. For this I tried to use the code below:
_pCredProvCredentialEvents->SetFieldInteractiveState(this,SFI_EDIT_TEXT,CPFIS_DISABLED);
At here SFI_EDIT_TEXT represents the object that I want to change it's properties and CPFIS_DISABLED shows it's should be disabled (at least i assume that is). But I didn't get any useful result. Anyone can able to help?
There are a several situations, where using SetFieldInteractiveState won't work. For example, if user have pressed "Submit" button, your's provider GetSerialization function will be called, and no GUI changes will be done by LogonUI until you return from GetSerialization. I think changes of GUI are made only between calls of your provider's functions.
P.S. I know, that question was asked long time ago, but in future, maybe, my answer can help others.
I am trying to create a simple dialog in MFC using Visual C++. My problem is that when I get the dialog on the screen and try to type in an Edit Box field, if I type the letter 'a' once, it appears in the edit box as 'aaaaaaaaaaa' (that's 12 a's). Furthermore, if I try to navigate around in the box using the arrow keys, the carat moves 12 characters at a time.
It's not just a display error, as the output from the editbox is still "aaaaaaaaaaaa".
I'd post code, but there's really none to post. I added the edit box using the Toolbox in Visual Studio and assigned a variable to it in my class so this isn't any sort of special edit box.
If anyone has any thoughts as to what might be happening it would be greatly appreciated. Unfortunately, I don't know where to begin.
Thank as always.
To debug this, add PreTranslateMessage function to your dialog, and see exactly how many times the keydown is being processed.
BOOL DialogName::PreTranslateMessage(MSG* pMsg)
{
if(pMsg->message==WM_KEYDOWN)
{
// TODO: see what is going on here
return TRUE; //do not dispatch this message, so keydown will have no effect
}
return CDialog::PreTranslateMessage(pMsg);
}
Are you capturing any events such as WM_KEYUP in your PreTranslateMessage() function or anywhere else in your app ?
If you have overridden the default handling for keyboard events, it might cause the symptoms you are seeing.
For some reason this brings back vague memories of early struggles with MFC. Have you looked for mutual recursion at all? I was forever doing something in one bit of the app that sent a message (unbeknown to me) that was picked up by another method that called the first method...
My guess is it's one of those smack the forehead ones; it gives me this nagging sense of deja vu that I can't make concrete.
If it's mutual recursion you should be able to see it in the call stack, if you can find the right place for a break point.
Is this happening for a fresh project, or can you recreate this problem in a fresh project?
It'll help discern whether it's something you've done in your code, or your install.
I installed service pack 2 in my WinXp 64 OS and the problem get solved for me :)