I am new at Qt and using Qt5.5 to create a http client application which will load a window with a fixed URL. After login in this window the other windows of same site should get the same session. At this purpose I have used global pointer jar of QNetworkCookieJar class and implemented on the following code for every window
Window1::Window1(QWidget *parent) :
QWidget(parent),
ui(new Ui::Window1)
{
ui->setupUi(this);
QUrl webURL("http://someURL");
ui->webView->show();
ui->webView->load(webURL);
ui->webView->page()->networkAccessManager()->setCookieJar(jar);
}
It solves the multiple authentication problem, but when I close any window and reopen it instantly it causes appcrash.
Please give me a suggestion on my problem. Thanks in advance.
From the Qt5 docs (http://doc.qt.io/qt-5/qnetworkaccessmanager.html#setCookieJar):
Note: QNetworkAccessManager takes ownership of the cookieJar object.
So the accessmanager will delete your jar instance. There might be your problem! I don't know enough about the webview/page/accessmanager to be sure about the lifetime of the manager, but it seems to be bound to the webview/your ui, so when it's closed+destroyed, your cookiejar will have gone, too.
As QNetworkCookieJar inherits from QObject, you might want to use a guarded QPointer<QNetworkCookieJar> jar instead of a simple QNetworkCookieJar* jar variable. Then, you will notice that your guarded pointer becomes null after the first window is closed/destroyed. That would a) verify my claim from the last paragraph and b) guard you against stale pointer accesses in the future (in fact, your program would no longer crash).
Thanks ThorngardSO..
I have found a solution using your answer. Here is my solution,
if(jar.isNull()==true){
qDebug()<<"object null";
QPointer <QNetworkCookieJar> jar_new = new QNetworkCookieJar(0);
ui->webView->page()->networkAccessManager()->setCookieJar(jar_new);
jar=jar_new;
}
else
ui->webView->page()->networkAccessManager()->setCookieJar(jar);
Related
I have this code:
QNetworkAccessManager man;
QNetworkRequest req(QUrl("URL"));
QString ua("HttpRequestDemo/0.1 (Win64) Qt/5.14.0");
req.setHeader(QNetworkRequest::UserAgentHeader, QVariant(ua));
QNetworkReply* reply = man.get(req);
QObject::connect(reply){
QByteArray read = reply->readLine();
QFile out("file.txt");
out.open(QIODevice::WriteOnly|QIODevice::Text);
out.write(read);
out.close();
})
This works on the main.cpp file, using the QCoreApplication, but I want to use the QApplication and download a specific data while pressing a button.
I put the same code on the on_pushButton_clicked() in the mainwindow.cpp file and it didn't even generate the file from the url.
The problem is that man and req go out of scope and are destroyed as soon as your on_pushButton_clicked() function returns, at which point the request probably hasn't even been sent yet.
You need to make sure that these objects outlive the current scope, either by making them members of the window class, or by allocating them on the heap and setting some QObject (maybe also the window class) as the parent.
The problem is that if you put the same code in a method like X you make QNetworkAccessManager a local variable that will be removed instantly that the connection is asynchronous. The solution is to make QNetworkAccessManager an attribute of the class.
*.h
private:
QNetworkAccessManager man;
*.cpp
void Klass::on_pushButton_clicked(){
QNetworkRequest req(QUrl("URL"));
QString ua("HttpRequestDemo/0.1 (Win64) Qt/5.14.2");
req.setHeader(QNetworkRequest::UserAgentHeader, QVariant(ua));
QNetworkReply* reply = man.get(req);
connect(reply, &QNetworkReply::finished, [&]() {
QByteArray read = reply->readAll();
QFile out("file.txt");
out.open(QIODevice::WriteOnly|QIODevice::Text);
out.write(read);
out.close();
reply->close();
reply->deleteLater();
})
}
If you are planning on potentially queuing very many downloads, I strongly recommend using libcurl in your Qt app. I was using QNetworkAccessManager to down 100+ financial quote files, and it would fail downloading ~ 1/3 of the time, and take a while to download. I switched to libcurl, and after figuring out how to get my crypto root certificates setup for https, it runs much faster, and almost never fails. I run it as a dll.
And yes, you will need to make sure the network manager, whether QNetworkManager or curl, doesn't go out of scope upon exiting the button handler. A more conventional pattern, although not necessarily better, is to either have a pointer to e.g. QNetworkManager in your parent class, and new it, or use a std::unique_ptr and std::make_unique (purportedly safer). Creating large objects on the stack can cause problems (in the old days, dare I say, stack overflows), and so is usually done on the heap. In this case, it's not very big, so it doesn't really matter. Alternatively, a form creating big objects might itself be created on the heap.
I have Created a simple QT application for my university assignment. What i have done is pop up a new QManinWindow from a Above QMainWindow. When i click a button from the main ui it will pop up a new QMainWindow object (Note Pad)
Note pad is also a QMainWindow object
My Problem is when I'm creating the object it takes some memory from the ram but when I'm closing it (pop up window) memory is not releasing. When each time I'm pressing a button memory is allocated but application does not relese the memory when im closing it. Please check the main screen of the app.
i just want to know how to release that memory. I have tried so many things but nothing worked well.
I have set the closeEvent public on NotePad class and I listen the close event from main object when its get triggered i have deleted the poped up object. But it cause ad unexpected stop.
void MainWindow::on_notePadBtn_clicked()
{
NotePad *notePad = new NotePad(this);
notePad->raise();
notePad->activateWindow();
notePad->show();
}
NotePad::NotePad(QWidget *parent) :QMainWindow(parent),ui(new Ui::NotePad) {
ui->setupUi(this);
this->setWindowTitle("Note Pad");
}
You don't really need to override closeEvent, Qt has Qt::WA_DeleteOnClose attribute, that does exactly what you want, you can use it like this:
//...
NotePad *notePad = new NotePad(this);
notePad->setAttribute(Qt::WA_DeleteOnClose);
notePad->raise();
notePad->activateWindow();
notePad->show();
//...
I'm not familiar with Qt.
But to my understanding if you use the operator new
you must use delete (in a scope where you have access to the pointer created with new).
Object *foo = new Object();
// Do stuff with foo...
delete foo;
// DO NOT use foo from now on.
Hope that helps a bit, maybe. Like I said I'm not familiar with Qt
so if you have doubts about how some features are implemented you should look at the their docs.
(cf: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3797.pdf §3.7.4p63)
Coming from making single-page applications with the visual WYSISWYG editor in JUCE, I'm having a bit of trouble figuring out how to invoke new windows (outside of the main GUI window). I made a test application that just has a small minimal main GUI that I created with the visual editor. It has a button "Make New Window." My goal is to be able to click that button and have a new window pop up and that this new window is a JUCE "GUI component," (AKA, the graphical / visual GUI editor file). Now, I actually have sort of achieved this, however, its throwing errors and assertions, so it would be great to get a very simple, step-by-step tutorial.
I studied the main.cpp file that the Projucer automatically created in order to get a feel for how they are creating a window. Here's what I did.
1) In my project, I added a new GUI Component (which becomes a class) and called it "InvokedWindow."
2) In my main GUI component class header, I added a new scoped pointer of type InvokedWindow: ScopedPointer<InvokedWindow> invokedWindow;
3) I created a new button in the main GUI editor called "Make New Window" and added this to the handler code:
newWindowPtr = new InvokedWindow; so that any time the button is hit, a new object of type InvokedWindow is created.
4) In the InvokedWindow class, in the constructor, on top of the automatically generated code, I added:
setUsingNativeTitleBar (true);
setCentrePosition(400, 400);
setVisible (true);
setResizable(false, false);
Which I sort of got from the main file of the JUCE application.
I also added a slider to this new window just to add functionality to it.
5) I added an overloaded function to let me close the window:
void InvokedWindow::closeButtonPressed()
{
delete this;
}
So, now when I run the app and click the make new window button, a new window does pop up, but I get an assertion:
/* Agh! You shouldn't add components directly to a ResizableWindow - this class
manages its child components automatically, and if you add your own it'll cause
trouble. Instead, use setContentComponent() to give it a component which
will be automatically resized and kept in the right place - then you can add
subcomponents to the content comp. See the notes for the ResizableWindow class
for more info.
If you really know what you're doing and want to avoid this assertion, just call
Component::addAndMakeVisible directly.
*/
Also, I'm able to close the window once and hit the button in the main GUI to create another instance of a newWindow, but closing it a second time leads to an error:
template <typename ObjectType>
struct ContainerDeletePolicy
{
static void destroy (ObjectType* object)
{
// If the line below triggers a compiler error, it means that you are using
// an incomplete type for ObjectType (for example, a type that is declared
// but not defined). This is a problem because then the following delete is
// undefined behaviour. The purpose of the sizeof is to capture this situation.
// If this was caused by a ScopedPointer to a forward-declared type, move the
// implementation of all methods trying to use the ScopedPointer (e.g. the destructor
// of the class owning it) into cpp files where they can see to the definition
// of ObjectType. This should fix the error.
ignoreUnused (sizeof (ObjectType));
delete object;
}
};
This is all a bit over my head. I was figuring it wouldn't be too bad to be able to create a new window, via a button. A new window that I could edit with the graphical GUI editor, but I'm not able to fully figure it out all on my own, through I did try. Could anyone post a step-by-step guide to doing this the correct way? I did post this at the JUCE forums, but due to my lack of GUI programming, I was unable to understand the solutions posted (my own fault), so I'm hoping to get a very simple guide to this. It would be very much appreciated. Thank you.
I figured it out. I needed to create:
A new GUI component (Remember, this is the visual editor in JUCE)
A class (I called it BasicWindow, based on the JUCE demo code) that acts as a shell to run this new window and holds the GUI component.
A JUCE SafePointer that makes a new object of type BasicWindow whenever the button is clicked and sets the attributes to that window.
Here is my code:
Referring to line 3) Inside the handler section of the button to create the new window:
basicWindow = new BasicWindow("Information", Colours::grey, DocumentWindow::allButtons);
basicWindow->setUsingNativeTitleBar(true);
basicWindow->setContentOwned(new InformationComponent(), true);// InformationComponent is my GUI editor component (the visual editor of JUCE)
basicWindow->centreWithSize(basicWindow->getWidth(), basicWindow->getHeight());
basicWindow->setVisible(true);
Referring to line 2) A .cpp file that defines what the BasicWindow is:
#include "../JuceLibraryCode/JuceHeader.h"
class BasicWindow : public DocumentWindow
{
private:
JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (BasicWindow)
public:
BasicWindow (const String& name, Colour backgroundColour, int buttonsNeeded)
: DocumentWindow (name, backgroundColour, buttonsNeeded)
{
}
void closeButtonPressed() override
{
delete this;
}
};
And referring to line 1) Make the GUI editor component, which this is easy to do. You just right add a new file in the JUCE file manager. "Add New GUI Component," then visually add all your elements and handler code.
My biggest issue was that I was using a JUCE ScopedPointer, so after deleting the object, the pointer pointing to it wasn't being set back to NULL. The SafePointer does this. If any more explanation is needed, I'm happy to help, as this was terrible for someone with not much GUI development "under his belt."
I am using Qt5, and trying to learn on how to make an application scriptable.
For this I created a main window that contains some text edits, labels, etc. I then added an option called "script console" to that forms' menu in order for me to open a second form containing just a text edit and a button called "Evaluate".
What I was aiming at was being able to use that second form and through Qt script engine be able to set or get values from my main form, and generally be able to script various functions.
What I tried doing was set up the engine like this
scriptingconsole::scriptingconsole(QWidget *parent) :
QDialog(parent),
ui(new Ui::scriptingconsole)
{
ui->setupUi(this);
QScriptValue appContext = myScriptEngine.newQObject(parent);
myScriptEngine.globalObject().setProperty("app", appContext);
}
I don't get what I was expecting though.
If I try to evaluate the expression "app" I get null as an output.
This works fine if I use myScriptEngine.newQObject(parent) with an object inside the current class (if instead of parent I enter this), but I want to be able to access object in other classes too (hopefully all public slots that are used by my app in general).
Does anyone know what I am doing wrong here and how can I use my scripting console
class to access public slots from my main window?
What's wrong?
I guess it's because you didn't explicitly pass the pointer, which points to your main form, to the constructor of your scriptingconsole. That's why you got NULL as a result. (NULL is default, as you can see QWidget *parent = 0 in every QWidget constructor)
This happens if your object is not dynamically instantiated.
Solution
Dynamically allocate scriptingconsole in your main form:
scriptingconsole* myScriptConsole;
//...
myScriptConsole = new scriptingconsole(this);
// ^^^^
// pass the pointer which points to parent widget
The Qt documentation of QScriptEngine::newQObject says:
Creates a QtScript object that wraps the given QObject object, using the given ownership. The given options control various aspects of the interaction with the resulting script object.
http://qt-project.org/doc/qt-4.8/qscriptengine.html#newQObject
i.e. it wraps a QObject.. You are probably passing NULL to newQObject, for whatever reason. Try setting a breakpoint and evaluating the value of 'parent'.
My friend and I have each created parts of a GUI using Qt 4. They both work independently and I am trying to integrate his form with the my main window. As of now this is the code I am using to try and load his form:
//connect buttons and such
connect(exitbtn, SIGNAL(triggered()),this,SLOT(terminated()));
connect(add, SIGNAL(triggered()),this,SLOT(add_rec()));
void MainWindowImpl::add_rec()
{
//form quits as soon as it loads...?
DialogImpl dia;//name of his form
dia.show();
}
I have included his header file. The program compiles but when I hit the trigger his form loads up for maybe half a second and then closes. Does anyone know what I am doing wrong?
You have almost get it right. This is because the RAII of C++. If you allocate the Dialog on stack, it would be destructed as soon as the function return.
Assuming MainWindowImpl inherits publically from QWidget, you're looking for this:
void MainWindowImpl::add_rec()
{
// passing "this" to the constructor makes sure dialog will be cleaned up.
// Note that DialogImpl will need a constructor that takes a
// QObject* parent parameter.
DialogImpl* dialog = new DialogImpl(this);
dialog->show();
}
Look at the Qt documentation for examples of how the constructors should look.
Apparently QT4 only allows one instance of an object at a time, however pointers are another matter. Change both the main.cpp and what ever your main window to look something like this:
DialogImpl *dia=new DialogImpl;
dia->show();