PySide2 Error: This application failed to start because no Qt platform plugin could be initialized
Add at the first:
import sys,os
import PySide2
dirname = os.path.dirname(PySide2.__file__)
plugin_path = os.path.join(dirname, 'plugins', 'platforms')
os.environ['QT_QPA_PLATFORM_PLUGIN_PATH'] = plugin_path
Error log
using ROS rqt visualization:
Could not import "pyqt" bindings of qt_gui_cpp library
The reason for the error
may be that the pyqt version is older or not installed.
pip install pydot pyqt5
Problem solving
Solution:
in the pro file of the project,
Add:
LIBS += -lpthread libwsock32 libws2_32
Open the debug button to see if the build suite has been modified or not
You need to ensure that the build kit is x86 or x64 relative to OpenCV
After switching to mingw32 bit, it runs successfully.
[problem description]
Qt5.9.11 is installed on windows10, and the compilation error is: error: lnk1158: unable to run “RC. Exe”
[problem location]
The path of rc.exe is not put into the environment variable
[solution]
Add the path “C:\program files (x86)\windows kits\8.1\bin\x86” to the environment variable path.
Restart qtcreator and the compilation is successful.
Vs2019 + QT parses the XML file and reports an error at doc.setcontent
Made a very low-level mistake. Record the process.
A QT project was established long ago. Now to add a function of parsing XML files using the qdom class, there is always an error in the sentence doc.setcontent (& amp; file) , and there is no error message. The relevant C + + codes are as follows:
QString error;
int line, column;
if (doc.setContent(&file, &error, &line, &column)) {
qDebug() << doc.toString(4);
}
else {
qDebug() << "Error:" << error << "in line " << line << "column" << column;
}
file.close();
When doc.setcontent (& amp; file, & amp; error, & amp; line, & amp; column) , critical error detected c00000374 is displayed
The first reaction is that the XML file is incorrectly written. For example, there is no space in the space, Chinese punctuation is entered, or the two sides of the tag are inconsistent
after repeatedly confirming that the XML file is correct, the stackoverflow search said that the relative path cannot be used, but the absolute path must be used… Another attempt of the absolute path is useless.
Create a new project and run it with the same code without error. Through careful comparison, it is found that in the new project, I added the XML class library
but not in the original project!
So far, add $(qtdir) \ include \ qtxml in the C/C + + include directory, add qt5xmld.lib [debug mode] and qt5xml. Lib [release mode] in the linker, and the operation is successful!
Finally, I found that if the XML file is written incorrectly, the above program can locate the error location. Direct reporting of fatal error/critical error or unresolved external symbols like this__ declspec(dllimport) public: __ Cdecl , the probability is that the Lib file link is wrong rather than the code problem. You need to check whether the environment is configured correctly.
A simple question has been wordy for a long time… Mainly to warn yourself that you must think more and think more about ways to expose the problem when you encounter a problem that has no solution on the Internet!
problem
AttributeError: 'QWidget' object has no attribute 'setCentralWidget'
reason
We can see setcentralwidget in QT help document that it belongs to the method of qmainwindow class and is defined separately in its class, so it cannot be called directly for its parent class QWidget.
void QMainWindow::setCentralWidget(QWidget *widget)
decided
Write QtWidgets.QWidget() converts QtWidgets.QMainWindow().
The following errors occur during vs operation
1. The QT module to be loaded may not be set in “QT project settings” in the project property page;
At this time, after locating the module that cannot be opened, add the corresponding module in “QT modules”, and recompile and run it.
catalogue
1. Error message:
2. Analysis
3. Solution
1. Error message:
D:\InstallSoftware\opencv\OpenCV-MinGW-Build-OpenCV-4.5.2-x64\x64\mingw\bin\libopencv_ calib3d452.dll:-1: error: file not recognized: File format not recognized
2. Analysis
This is because the opencv compiled file version is different from the QT project version. You should choose the correct version of the toolkit.
3. Solution
For example, my opencv compilation file is opencv build_ 64 bit, then select MinGW 64 bit for the project.
catalogue
1. Error message:
2. Analysis:
3. Solution:
1. Error message:
F:\test\Qt-Demo\mainwindow.cpp:55: error: use of undeclared identifier ‘CV_ BGR2RGB’
2. Analysis:
Because opencv is used CV_ Bgr2gray did not declare it. Therefore, an undeclared identifier is prompted.
3. Solution:
Reference the following code in the header file:
#include < opencv2\imgproc\types_ c.h>
Problem description
The qvtkwidget control is used in QT’s interface. When clicking the close button in the upper right corner of the window, an error is reported: wglmakecurrent failed in makecurrent(), error: the handle is invalid .
Solution:
By overriding the void closeevent (qcloseevent * event) function, manually delete all qvtkwidget type controls, and then close the window.
Example
The qvtkwidget type controls in the QT design interface are as follows:
mymainwindow. H
class MyMainWindow : public QMainWindow
{
Q_OBJECT
public:
MyMainWindow(QWidget *parent = Q_NULLPTR);
protected:
void closeEvent(QCloseEvent *event);
private:
Ui::MainWindow ui;
};
mymainwindow.cpp
MyMainWindow::MyMainWindow(QWidget *parent): QMainWindow(parent)
{
ui.setupUi(this);
}
void MyMainWindow::closeEvent(QCloseEvent *event) {
delete ui.qvtkWidget;
delete ui.qvtkWidget_2;
delete ui.qvtkWidget_3;
delete ui.qvtkWidget_4;
event->accept();
}
Postscript
I don’t know whether such hasty delete processing will cause other problems. I hope you can make more corrections.
Recently, when developing with QT4, there was a problem that Q could not be recognized_ DECLARE_ The error code of the metatype macro was transplanted from Qt5. I thought it was not supported by QT4. After checking later, I found that the qmetatype. H header file must be included in QT4, and only qvariant needs to be included in Qt5.