PyQt多窗口调用

常常有人问到如何在一个主窗口中打开一个对话框，而后在确认对话框以后，开启另外一个窗口进行后续操做，
要求主窗口和最终的窗口之间都能响应用户操做，也就是非模态窗口。随手写了几行代码，简要示意。

:::python
#!/usr/bin/python
# -*- coding: utf-8 -*-
# Gui (imgui@qq.com)
# License: BSD

from PyQt4.QtCore import *
from PyQt4.QtGui import *
import sys


class W1(QWidget):
    def __init__(self, parent=None):
        super(W1, self).__init__(parent)
        self.btn = QPushButton('Click1')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)

        self.btn.clicked.connect(self.fireupWindows2)

    def fireupWindows2(self):
        w2 = W2()
        if w2.exec_():
            self.w3 = W3()    # 须要经过self实例化为全局变量，不加self的话，一运行就被回收，也就没法显示。
            self.w3.show()


class W2(QDialog):
    def __init__(self, parent=None):
        super(W2, self).__init__(parent)

        self.btn = QPushButton('Click2')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)

        self.btn.clicked.connect(self.fireupWindows3)

    def fireupWindows3(self):
        self.accept()


class W3(QWidget):
    def __init__(self, parent=None):
        super(W3, self).__init__(parent)
        self.resize(300, 300)
        self.btn = QLabel('The Last Window')

        vb = QVBoxLayout()
        vb.addWidget(self.btn)
        self.setLayout(vb)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = W1()
    w.show()
    sys.exit(app.exec_())