Как привязать QGridLayout к размеру окна?

Цель: при изменении размера окна, изменялся размер QGridLayout

mainwindows.ui

<?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>877</width>
    <height>501</height>
   </rect>
  </property>
  <property name="sizePolicy">
   <sizepolicy hsizetype="Fixed" vsizetype="Fixed">
    <horstretch>0</horstretch>
    <verstretch>0</verstretch>
   </sizepolicy>
  </property>
  <property name="maximumSize">
   <size>
    <width>16777215</width>
    <height>16777215</height>
   </size>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <property name="enabled">
    <bool>true</bool>
   </property>
   <widget class="QWidget" name="layoutWidget">
    <property name="geometry">
     <rect>
      <x>8</x>
      <y>10</y>
      <width>861</width>
      <height>481</height>
     </rect>
    </property>
    <layout class="QGridLayout" name="gridLayout">
     <item row="0" column="0">
      <widget class="QLineEdit" name="leVersion"/>
     </item>
     <item row="0" column="1">
      <widget class="QPushButton" name="btnVersoin">
       <property name="text">
        <string>Версия ПО</string>
       </property>
      </widget>
     </item>
     <item row="0" column="2">
      <widget class="QPushButton" name="btnStart">
       <property name="text">
        <string>Старт</string>
       </property>
      </widget>
     </item>
     <item row="0" column="3">
      <widget class="QPushButton" name="btnStop">
       <property name="text">
        <string>Стоп</string>
       </property>
      </widget>
     </item>
     <item row="1" column="0" rowspan="2" colspan="2">
      <widget class="QTextEdit" name="textEdit"/>
     </item>
     <item row="1" column="2" colspan="2">
      <widget class="QwtPlot" name="plot1" native="true"/>
     </item>
     <item row="2" column="2" colspan="2">
      <widget class="QwtPlot" name="plot2" native="true"/>
     </item>
     <item row="3" column="2">
      <widget class="QLineEdit" name="leFixTemp">
       <property name="font">
        <font>
         <pointsize>12</pointsize>
        </font>
       </property>
       <property name="layoutDirection">
        <enum>Qt::LeftToRight</enum>
       </property>
       <property name="alignment">
        <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
       </property>
      </widget>
     </item>
     <item row="3" column="3">
      <widget class="QPushButton" name="btnFixTemp">
       <property name="font">
        <font>
         <pointsize>12</pointsize>
        </font>
       </property>
       <property name="text">
        <string>  Зафиксировать температуру  </string>
       </property>
      </widget>
     </item>
    </layout>
   </widget>
  </widget>
  <action name="actionasdas">
   <property name="text">
    <string>asdas</string>
   </property>
  </action>
  <action name="actiondasd">
   <property name="text">
    <string>dasd</string>
   </property>
  </action>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <customwidgets>
  <customwidget>
   <class>QwtPlot</class>
   <extends>QWidget</extends>
   <header>qwt_plot.h</header>
   <container>1</container>
  </customwidget>
 </customwidgets>
 <resources/>
 <connections/>
</ui>

Пример растягивания: