如何使用程序 Qt Designer 将 QWidget 放在中间而不依赖于 Pyside2 中的屏幕尺寸？

由于没有 python 的答案，我发布了这个答案，它是Qt 官方示例的翻译。

import sys

from PySide2 import QtCore, QtWidgets


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)

    w = QtWidgets.QWidget()
    w.resize(640, 480)

    w.setGeometry(
        QtWidgets.QStyle.alignedRect(
            QtCore.Qt.LeftToRight,
            QtCore.Qt.AlignCenter,
            w.size(),
            QtWidgets.QApplication.instance().primaryScreen().availableGeometry()
            # or
            # QtWidgets.QApplication.instance().desktop().availableGeometry(),
        )
    )
    w.show()

    sys.exit(app.exec_())

更新：

你可以在 QGridLayout 中将拉伸设置为第一列和第三列，类似于行：

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>800</width>
    <height>600</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <layout class="QGridLayout" name="gridLayout" rowstretch="1,0,1" columnstretch="1,0,1">
    <property name="leftMargin">
     <number>0</number>
    </property>
    <property name="topMargin">
     <number>0</number>
    </property>
    <property name="rightMargin">
     <number>0</number>
    </property>
    <property name="bottomMargin">
     <number>0</number>
    </property>
    <item row="0" column="1">
     <spacer name="verticalSpacer">
      <property name="orientation">
       <enum>Qt::Vertical</enum>
      </property>
      <property name="sizeHint" stdset="0">
       <size>
        <width>20</width>
        <height>142</height>
       </size>
      </property>
     </spacer>
    </item>
    <item row="1" column="0">
     <spacer name="horizontalSpacer">
      <property name="orientation">
       <enum>Qt::Horizontal</enum>
      </property>
      <property name="sizeHint" stdset="0">
       <size>
        <width>254</width>
        <height>20</height>
       </size>
      </property>
     </spacer>
    </item>
    <item row="1" column="1">
     <widget class="QWidget" name="widget" native="true">
      <property name="styleSheet">
       <string notr="true">background-color: rgb(239, 41, 41);</string>
      </property>
      <layout class="QVBoxLayout" name="verticalLayout">
       <item>
        <widget class="QLabel" name="label">
         <property name="font">
          <font>
           <pointsize>21</pointsize>
          </font>
         </property>
         <property name="text">
          <string>Text</string>
         </property>
         <property name="alignment">
          <set>Qt::AlignCenter</set>
         </property>
        </widget>
       </item>
       <item>
        <widget class="QTextEdit" name="textEdit">
         <property name="styleSheet">
          <string notr="true">background-color: rgb(255, 255, 255);</string>
         </property>
        </widget>
       </item>
      </layout>
     </widget>
    </item>
    <item row="1" column="2">
     <spacer name="horizontalSpacer_2">
      <property name="orientation">
       <enum>Qt::Horizontal</enum>
      </property>
      <property name="sizeHint" stdset="0">
       <size>
        <width>254</width>
        <height>20</height>
       </size>
      </property>
     </spacer>
    </item>
    <item row="2" column="1">
     <spacer name="verticalSpacer_2">
      <property name="orientation">
       <enum>Qt::Vertical</enum>
      </property>
      <property name="sizeHint" stdset="0">
       <size>
        <width>20</width>
        <height>141</height>
       </size>
      </property>
     </spacer>
    </item>
   </layout>
  </widget>
  <widget class="QMenuBar" name="menubar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>800</width>
     <height>24</height>
    </rect>
   </property>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
 </widget>
 <resources/>
 <connections/>
</ui>