title: Add a QPushButton into a QTableWidgetItem in a QTableWidget, How to make it Qt::AlignHCenter
body: <pre><code>for(int i=0; i&lt;page.size(); i++){
      User user= Poco::AnyCast&lt;User&gt;(*it);
      ui.table-&gt;setItem(i,0,new QTableWidgetItem(user.userName)); 
      ui.table-&gt;setItem(i,1,new QTableWidgetItem(user.sex));
      ui.table-&gt;setItem(i,2,new QTableWidgetItem(user.age));
  
      QPushButton* btn_edit = new QPushButton();
      btn_edit = new QPushButton();
      btn_edit-&gt;setText("Edit");
      ui.table-&gt;setCellWidget(i,3,(QWidget*)btn_edit);
  
      ++it;
  }
  </code></pre>
  
  <p>I add a QPushButton into the cell with the function setCellWidget(),
  I know, if it's a QTableWidgetItem, I can use :</p>
  
  <pre><code>ui.table-&gt;item(0,3)-&gt;setTextAlignment(QT::AlignHCenter)
  </code></pre>
  
  <p>But it is a Widget, </p>
  
  <pre><code>QTableWidgetItem item = ui.table-&gt;item(0,3); 
  </code></pre>
  
  <p>the item is null.</p>
  
  <p>I can get the cell by use </p>
  
  <pre><code>ui.table-&gt;cellWidget(0,3).
  </code></pre>
  
  <p>How should I do to make the button centered in the cell?</p>