QLabel 在 QMainWindow 上表现得很奇怪

Question

我想创建一个带有 Qlabel 的 gui，在其中显示图像，之后我想在图像上进行选择（矩形）并将选择另存为计算机中的另一个图像。但我有一个问题：

首先，当我创建 gui（没有 QtDesigner）时，一切正常，但是当我在 QtDesigner 上创建 gui 时，我想在我的框标签上显示我的新图像和 KpeWindow 类，但它显示在左上角，为什么？

gui.ui:

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>GUI</class>
 <widget class="QMainWindow" name="GUI">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>770</width>
    <height>527</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>GUI</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QPushButton" name="clear_btn">
    <property name="geometry">
     <rect>
      <x>10</x>
      <y>220</y>
      <width>71</width>
      <height>32</height>
     </rect>
    </property>
    <property name="text">
     <string>clear</string>
    </property>
   </widget>
   <widget class="QPushButton" name="save_btn">
    <property name="geometry">
     <rect>
      <x>70</x>
      <y>220</y>
      <width>69</width>
      <height>32</height>
     </rect>
    </property>
    <property name="text">
     <string>save</string>
    </property>
   </widget>
   <widget class="QPushButton" name="load_btn">
    <property name="geometry">
     <rect>
      <x>130</x>
      <y>220</y>
      <width>67</width>
      <height>32</height>
     </rect>
    </property>
    <property name="text">
     <string>load</string>
    </property>
   </widget>
   <widget class="QLabel" name="grafic">
    <property name="geometry">
     <rect>
      <x>218</x>
      <y>12</y>
      <width>531</width>
      <height>411</height>
     </rect>
    </property>
    <property name="frameShape">
     <enum>QFrame::Box</enum>
    </property>
    <property name="text">
     <string/>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>770</width>
     <height>22</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

第一部分代码：

import sys
from PyQt5 import QtCore, QtWidgets
from PyQt5.QtCore import Qt, QRect
from PyQt5.QtGui import QPixmap
from PyQt5.QtWidgets import QApplication
from PyQt5.uic import loadUi

class KpeWindow(QtWidgets.QLabel):
    def __init__(self, parent=None):
        QtWidgets.QLabel.__init__(self,parent)
        self.selection = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle, self)


    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton:
            position = QtCore.QPoint(event.pos())
            if self.selection.isVisible():
                # visible selection
                print(self.upper_left.manhattanLength())
                if (self.upper_left - position).manhattanLength() < 20:
                    # close to upper left corner, drag it
                    self.mode = "drag_upper_left"
                elif (self.lower_right - position).manhattanLength() < 20:
                    # close to lower right corner, drag it
                    self.mode = "drag_lower_right"
                else:
                    # clicked somewhere else, hide selection
                    self.selection.hide()
            else:
                # no visible selection, start new selection
                self.upper_left = position
                self.lower_right = position
                self.mode = "drag_lower_right"
                self.selection.show()

    def mouseMoveEvent(self, event):
        '''
            Mouse moved. If selection is visible, drag it according to drag mode.
        '''

        if self.selection.isVisible():
            # visible selection
            if self.mode is "drag_lower_right":
                self.lower_right = QtCore.QPoint(event.pos())
                # print(str(self.lower_right))
            elif self.mode is "drag_upper_left":
                self.upper_left = QtCore.QPoint(event.pos())
                # print(str(self.upper_left))
            # update geometry
            self.selection.setGeometry(QtCore.QRect(self.upper_left, self.lower_right).normalized())

没有 QtDesigner 的主窗口

class MainWindow(QtWidgets.QWidget):
        def __init__(self):
            super(MainWindow, self).__init__()
            QtWidgets.QMainWindow.__init__(self)
            layout = QtWidgets.QVBoxLayout(self)
            label = KpeWindow(self)
            pixmap = QPixmap("image.JPG")
            label.setPixmap(pixmap)
            layout.addWidget(label)
            label.setFocusPolicy(Qt.StrongFocus)
            self.setFocusProxy(label)
            label.setFocus(True)
            self.setLayout(layout)
            self.setFixedSize(640, 480)
            self.show()

    if __name__ == '__main__':
        app = QApplication(sys.argv)
        mainWin = MainWindow()
        mainWin.show()
        sys.exit(app.exec_())

带有 QtDesigner 的主窗口：

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        loadUi('GUI/gui.ui', self)
        #self.grafic <-- this is the box label
        self.grafic = KpeWindow(self)
        pixmap = QPixmap("image.JPG")
        self.grafic.setPixmap(pixmap)
        self.grafic.setFocusPolicy(Qt.StrongFocus)
        self.setFocusProxy(self.grafic)
        self.grafic.setFocus(True)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    mainWin = MainWindow()
    mainWin.show()
    sys.exit(app.exec_())

Answer 1

错误的原因是您假设如果您创建一个与 QLabel 同名的小部件，它将替换它，但这是错误的，您正在创建另一个 QLabel，其父窗口是窗口，因此它将是位于左上角。

所以有两种解决方案：

1. 提升KpeWindow为图形，this answer中有例子。

2. 通过布局设置QLabel中的KpeWindow。

from PyQt5 import QtCore, QtGui, QtWidgets, uic

class KpeWindow(QtWidgets.QLabel):
    # ...

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        uic.loadUi('GUI/gui.ui', self)
        kpe_window = KpeWindow()
        pixmap = QtGui.QPixmap("image.JPG")
        kpe_window.setPixmap(pixmap)
        kpe_window.setFocusPolicy(QtCore.Qt.StrongFocus)
        self.setFocusProxy(kpe_window)
        kpe_window.setFocus(True)
        lay = QtWidgets.QVBoxLayout(self.grafic)
        lay.addWidget(kpe_window)


if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    mainWin = MainWindow()
    mainWin.show()
    sys.exit(app.exec_())

第二种方案是最简单的。