用PyQt4实例化QWidget的需求

Question

This code works:

from PyQt4 import QtGui
import sys

app=QtGui.QApplication(sys.argv)


window1=QtGui.QWidget()
window1.show()

window2=QtGui.QWidget()
window2.show()

But this doesnt:

from PyQt4.QtGui import *
import sys

class window(QMainWindow):
    def __init__(self):
        super(window, self).__init__()
        self.w=QWidget()
        self.w.show()

app=QApplication(sys.argv)
window()
window()

How can i create 2 windows by instancing the class window? I don't get it with Qt, with Tkinter it is very easy to figure out...

EDIT: The question above is meant for creating some windows by clicking on a button in the systray. As you can see when executing the code below, it works, but there is just one window shown at any time, eg if i clicked twice the context menu of the systray icon to create two windows. I don't see where it comes from...

import sys
from PyQt4.QtGui import *


class Note(QMainWindow):
    def __init__(self):
        super(Note,self).__init__()
        self.w=QWidget()
        self.setWindowTitle("Note")
        self.setCentralWidget(self.w)

class main():
    def __init__(self):
        self.app = QApplication(sys.argv)

        self.trayIcon = QSystemTrayIcon(QIcon("J:\\python\\SimpleNotes.ico"), self.app)
        self.menu = QMenu()

        self.newWindow = self.menu.addAction("new Note")
        self.separator = self.menu.addSeparator()
        self.exitAction = self.menu.addAction("Exit")

        self.exitAction.triggered.connect(self.close)
        self.newWindow.triggered.connect(self.newNote)
        self.trayIcon.setContextMenu(self.menu)
        self.trayIcon.show()

        self.app.exec()

    def newNote(self):
        print("Create new note entry has been clicked")
        self.note=Note()
        self.note.show()

    def close(self):
        self.trayIcon.hide()
        self.app.exit()
        print("Exit menu entry has been clicked")

main()

EDIT2: Got it! The problem can be solved by coding it this way:

class main():
    def __init__(self):
        self.notes=[]
        ...

    def newNote(self):
        note=Note()
        note.show()
        self.notes.append(note)

Though still I don't know why now it works, or even no window occurs if you delete the line "self.notes.append(note)". But hah, it works!

Answer 1

Try something like this:

from PyQt4.QtGui import *
import sys

class window(QMainWindow):
    def __init__(self):
        super(window, self).__init__()
        self.w=QWidget()
        self.setCentralWidget(self.w)

app=QApplication(sys.argv)
w1 = window()
w1.show()
w2 = window()
w2.show()
app.exec()

You need to show the top-level containers, not the internal widgets. And you probably wanted that widget to show inside your main window and not as an independent window.

The problem with your updated code is that when the click "Add note" a second time, you replace the member self.note with a new window. The previous window is therefore not referenced anywhere after the call, and gets destroyed.
If you want to keep multiple windows open, you need to keep a handle on all of them as long as you need them.

Warning: I don't actually know python, so the naive use of a list might not be a good idea - I don't know.

Try this:

class main():
    def __init__(self):
        self.app = QApplication(sys.argv)
        self.app.setQuitOnLastWindowClosed(False);
        self.notes = []
        ...

    def newNote(self):
        print("Create new note entry has been clicked")
        note=Note()
        note.show()
        self.notes.append(note)

The setQuitOnLastWindowClosed part is necessary in your use case, otherwise app.exec would exit once you've closed all the note windows, and your app would exit at that point - doesn't look like that's what you want to happen.

Note: that's not a usual use of QMainWindow . That's a "heavy" class, usually use as the sole main window of a "complete" GUI app, with a menu, toolbar(s), status bar, etc. Using a simple QWidget with a QTextEdit and maybe a couple of buttons sounds better for this use case. In fact you could probably get away with deriving your Note from QTextEdit and implementing just a context menu.