I have a QT-project (using C++) where instances of a certain user-defined QGraphicsItem called Person move around the scene. Sometimes those Persons interact so that some of them change color.
Now I want to put a text field in the window and display counts of how many I have of each color. But since the change occurs within the call to the Person::advance-method I want to create a text field that can be updated from within these.
I could easily display some text by adding the following code to my main.cpp:
QGraphicsSimpleTextItem *text1 = new QGraphicsSimpleTextItem;
text1->setPos(-200, -150);
text1->setText("This is an arbitrary English sentence");
scene.addItem(text1);
but I do not know how to access and alter the text of this variable text1 from within the advance-method of the Persons in my scene. What is a good strategy for this?
Should I create a global variable keeping track of the count, and if I do, how can I then update the text field? Or should the text not even be on my QGraphicsScene, but rather be defined in some other more appropriate place where it is callable from everywhere in the program? Is there a generic way of doing this?
You could subclass QGraphicsObject instead of QGraphicsItem, that would allow you to use signals from within the Person class. Then just emit a signal to a slot that counts the items and changes the text of text1.
What I would do is move your graphics view to a new QWidget type class (like QMainWindow). This is to make it easier to handle signals and slots, and it will also allow you to use member variables. It will also be cleaner than doing everything in main.cpp.
You could have your text1 variable as a member variable of this MainWindow class. This would make accessing it easy.
Your slot in the MainWindow class could look something like this:
MainWindow::countItems()
{
int redcount = 0;
int greencount = 0;
int bluecount = 0;
// iterate through your `Person` items and check their colors and count them
text1->setText(QString("Red items: %1, Green items: %2, Blue items: %3").arg(redcount).arg(greencount).arg(bluecount));
}
You can improve the logic, but this is just a basic example.
Related
A text editor app has multiple widgets, of multiple types: QTextEdit, QTableView, QTreeView. All of them need to have rich text editing functions.
This code enables the strikethrough function to work on just ONE specific widget. How to make it work on any widget that holds the currently selected text?
ui->toDoListTextEdit needs to be replaced with a call to the widget that holds the selection fmt, or the cursor?. How to do this, considering that there are three different types of widgets?
void MainWindow::on_actionStrike_triggered()
{
//put in strikethrough
QTextCharFormat fmt;
fmt.setFontStrikeOut(true);
//blend selection
QTextCursor cursor = ui->toDoListTextEdit->textCursor();
if (!cursor.hasSelection())
cursor.select(QTextCursor::WordUnderCursor);
cursor.mergeCharFormat(fmt);
ui->toDoListTextEdit->mergeCurrentCharFormat(fmt);
}
Take a look at MVC pattern, create own model which will store text to display, subclass from QTextView and emit signals to change model's data(text), same goes to model, implement signals to change custom QTextView class.
The application that I'm building is supposed to create, destroy, and manipluate widgets that I've created
The problem is I'm not making a simple program with nice buttons where everything is symmetrical and needs to be evenly spaced and handled via a layout that will automatically move everything around and space it.
And yet, the only way I know of is to manually instance a layout and add the widgets to it, but then I can't set the coordinates of them
How can I simply instance my widget, and add it to the project generated frame?
This is how I'm instantiating my class, in which case I then set my own parameters:
Tile *tile = new Tile;
tile->setImg("://Images/placeholderTile.png");
tile->setCol(true);
tile->setGeometry(retX(line),retY(line),50,50);
To reiterate, I want to add my own widgets to a frame outside of the editor (only by code), and be able to manually move them around the frame by code.
I don't see an ".addWidget() as a method accessible from the QFrame, and yet they can be children within the designer, why can't I do this by code? Whenever I try to do it manually and add them to any layout, any attempt I make to manually set the widgets location doesn't do anything. I haven't overridden the setGeometry
I fixed my problem
After 2 hours of continual searching I finally came across my answer
I never thought that you could set the parent of a widget by code, as I thought you strictly had to add it in as a child of something else, not the reverse and declare that it should have a parent
So, by simply adding the line:
tile->setParent(ui->frame);
completely fixed my problem.
I will change this post back and submit the answer tomorrow when I'm allowed to by this site.
Thank you to those who actually came though. I'm just glad I managed to fix it before that.
All you need is to pass the parent to the widget's constructor:
Tile *tile = new Tile(ui->frame); // <-- here
tile->setImg("://Images/placeholderTile.png");
tile->setCol(true);
tile->setGeometry(retX(line),retY(line),50,50);
Since Tile is your own class, you should definitely have a Qt-style, parent-taking explicit constructor for it:
class Tile : public QWidget {
...
public:
explicit Tile(QWidget * parent = 0) : QWidget(parent) { ... }
};
Another approach is to write your own layout that would know about the relationships that are to be held between your objects. After you do it once, writing custom layouts isn't that hard.
I'm having issues with formulating the question but this is what I want to do with my application.
A user can select one or multiple image-files (.ppm), and they are displayed in some sort of legend, with their filename underneath. The information of these images is stored in a structure. (This structure contains the image path, name, and other info).
Now I want to give the user the chance to change the name of the selected images, and uses this name in the rest of the application. So I would have to change the name in the structure.
I could do this by adding textfields in the legend, where users can type the desired name, but how can I get the input from this textfield if I don't know which one is alterred?
If the user selects 6 images, I need 6 new textfields in the legend, but how can I address the correct one?
struct[2].name = input2.getText();
I also thought about doing it with some sort of wizard, with 6 pages where the names can be changed, but I don't know how I can adress the correct textfield.
Any help would be welcome, thanks!!
If you want to allow users to rename multiple files at one time, you may want to create a wizard. In the wizard you could display each picture they selected (one at a time) and allow them to rename each picture (one at a time). Otherwise it will be confusing to the user and harder for you to manage.
When generating the wizard, I would use the information structure to associate the picture with the textfield.
Qt, signals and slots are your friend here.
When you setup the textfields for the name, assuming you use something like a QLineEdit object, connect to a relevant signal, such as editingFinished(). Make the connection to the slot of the Object that stores the structure. The receiving slot then updates the appropriate information.
So, assuming your struct is in an object derived from QObject, you can do something like this: -
struct DataStruct // the struct storing the underlying data
{
QString name;
QLineEdit* linkedEditWidget; // widget for user to change text
};
class MainObject : public QObject
{
Q_OBJECT // required for signals and slots
public slots:
void UpdateText();
private:
const int NUM_STRUCTS = 10; // initialisation in C++ 11
DataStruct myStructs[NUM_STRUCTS]; // a number of structs
};
When you initialize the array of structs and the LineEdit widgets, store a pointer to the matching LineEdit widget in each myStruct and connect the widgets' editingFinished signals to the MainObject updateText() slot. It would be a good idea to use weak smart pointers here, but I'll use a standard pointer, to keep things simple.
When you receive notification that the text has changed, you'll need to match up the caller with the LineEdit* in the struct. Note that QObject::sender() will return the pointer to the object that sent the message: -
void MainObject::UpdateText()
{
QObject* theSendingWidget = sender();
for(int i=0; i<NUM_STRUCTS; ++i) // assuming NUM_STRUCTS is already defined
{
if(myStructs[i].linkedEditWidget == theSendingWidget)
{
// update the name in the data struct
myStructs[i].name = (static_cast<QLineEdit*>(theSendingWidget))->text();
return; // our work is done.
}
}
}
Finally, you'd probably make life easier for yourself by storing the data in Qt model objects, rather than using a plain struct. I suggest reading up on Model / View programming and the MVC design pattern
This questions to me reeks of maybe a lack of understanding of C++, as the possibilities I've considered for my problem all seem to make no sense on why this could be occuring. Feedback appreciated.
I'm using the form designer to create a form class with a table in it. I'm trying to replace the table with another table generated in a helper class. I'm only doing this so I can (hopefully) maintain the nice grid layout I've designed, and through pointer manipulation, get the replacement I desire. Here's some code snippets from the table form constructor and relevant calls :
//tableData is defined in the header file as a QTableWidget*
tableData = this->findChild<QTableWidget *>("tableData");
....
setup();
void setup(){
tableData = Utilities::createTable(this->file, tableDelim);
//createTable returns QTableWidget*
... other assignments, and label text updates, which seem to all work
}
My understanding is that tableData is a pointer, and if printed, will give the address of the QTableWidget from the layout. So then if I create a QTableWidget* and then assign tableData to that, tableData should now point to the new widget. Instead, I see only a blank screen.
I tried checking what the tableData pointer is before I assign it to the new QTableWidget*, and after. The second pointer shown is what is generated by createTable() :
QTableWidget(0x101272d40, name = "tableData") QTableWidget(0x10127b3b0, name = "test_sample2.nuc.stats")
QTableWidget(0x10127b3b0, name = "test_sample2.nuc.stats") QTableWidget(0x10127b3b0, name = "test_sample2.nuc.stats")
It seems the pointer is being reassigned, but the table drawn isn't the right one.
What gives?
My understanding is that you want to design the table layout in designer but fill in the data from an external source.
I would suggest, to just use the QTableWidget that is created in setupUi() and modify Utilities::createTable() such that it becomes Utilities::populateTable(QTableWidget & table, <all the other parameters you need>). (Or use QTableWidget * if you prefer - however I like putting the non-zero assertion responsibility on the caller...)
Apart from that, I agree with Sebastian Lange.
You are right with your assumption. You do set a variable to be a pointer to a object and next you set the variable to be a pointer to another object. You never change any objects, just your variable which is not used to display anything.
You would need to do something like:
//tableData is defined in the header file as a QTableWidget*
tableData = this->findChild<QTableWidget *>("tableData");
parentLayout = tableData->parent()->layout(); //Get the parent widget to add another table.
parentLayout->removeWidget(tableData);
delete tableData;
parentLayout->addWidget(createTable());
You need to use pTheContainerOfTheOriginalTableWidget->addWidget(tableData); See here: http://qt-project.org/forums/viewthread/16547
Be sure you remove the original tableWidget so you don't have two (I assume you don't want two).
If I understand you correctly we have such situation.
call of setupUi (which generated by qt tootls),
there there is something like this(pseudo code):
oldTablePtr = new QTableWidget(parent);
someLayout->addWidget(oldTablePtr);
So parent and layout hold value of oldTablePtr.
And if you set variable oldTablePtr nothing changed.
parent send QPaintEvent to oldTablePtr.
So you need call delete oldTablePtr, that remove this widget from list of childs of parent, and move newTablePtr to the same layout.
There's no need to replace it in code, you can do it in Qt Designer. Just place QTableWidget on form, then rightclick it and choose Promote widget in menu, then you will need just enter your classname.
Currently I don't have Qt Designer near me, so edits will be appreciated.
I am in the process of developing a html editor in Qt for one of my university assignments, and i am having a problem regarding naming of some variables.
the problem is this:
when the user decides to load their "project" the program iterates through the folder and finds how many .html files are in there, it then creates tabs for them to be displayed in.
I have a custom QTextEdit which has a customer completer and syntax highlighting etc. the problem i am having at the moment is how to create them depending on the number needed.
i create a QStringList of file names:
QStringList m_files;
m_files = aDialog.m_loadDirectory->entryList(QStringList("*.html"),QDir::Files|QDir::NoSymLinks);
then i iterate through each one of the list:
for(int i=0; i<m_files.count();i++)
{
}
and for each one i need to create a new custom QtextEdit
TextEdit *name = new TextEdit;
then add to the tab
tabs->addTab(name,"someTitle");
but as each TextEdit needs to be different for each tab (i think this is correct) i need a different Variable name for each one.
i thought about creating a list/array of TextEdit objects but as i dont know how many i need to use, i could end up easily with too many (wasted memory) or not enough..
any ideas on how i can get around this?
one thought..
would it be possible to create a TextEdit object before the loop
then make a copy of that object in the loop and add the copied object to the tab? (still variable naming problem...)
thanks
but as each TextEdit needs to be different for each tab (I think this is correct)
Yes, you need a different TextEdit in each tab.
I need a different Variable name for each one.
No, you don't need a different variable name for each one. You need different objects, but variable names don't have much to do with that.
A simple:
for (...) {
TextEdit *te = new TextEdit(...);
// set up that text edit in whatever way you need
tabs->addWidget(te, "foo");
}
does exactly what you want. The variable name te is completely irrelevant (it won't even appear in the executable outside of debugging symbols). Each time through the loop, you'll be working on a separate TextEdit instance.
If you need to refer to that TextEdit by name at runtime, you can keep all your widgets in a collection, a QMap for instance.
QMap<QString, QWidget*> all_editors;
...
for (...) {
TextEdit *te = ...;
all_editors[filename] = te;
...
}
You have discarded quickly the only viable solution : put your text edits in a collection. The textedit have to be created with new, so the collection itself will not waste space.
You can use a QPair<QTabWidget*, QTextEdit*> for simplest cases. For more complicated cases create a custom widget, and just make a list of those.
Copying a QObject is a really bad idea. I think the copy constructor is private so you will not even be able to do that