可以将所有组合框的每个TextChanged事件设置为同一个事件处理程序。

 comboBox1.TextChanged += CommonComboTextChanged;
 comboBox2.TextChanged += CommonComboTextChanged;
 comboBox3.TextChanged += CommonComboTextChanged;
 comboBox4.TextChanged += CommonComboTextChanged;
private void CommonComboTextChanged(object sender, EventArgs e)
    ComboBox cbo = sender as ComboBox;
    richTextBox.Text = cbo.Text;
}

但是，如果将组合体的DropDownStyle更改为ComboBoxStyle.DropDownList，则可以使用SelectedIndexChanged事件，只有当用户使用DropDown列表更改所选项时才会触发该事件。

 comboBox1.SelectedIndexChanged += CommonComboIndexChanged;
 comboBox2.SelectedIndexChanged += CommonComboIndexChanged;;
 comboBox3.SelectedIndexChanged += CommonComboIndexChanged;;
 comboBox4.SelectedIndexChanged += CommonComboIndexChanged;;
 private void CommonComboIndexChanged;(object sender, EventArgs e)
    ComboBox cbo = sender as ComboBox;
    richTextBox.Text = cbo.Text;
 }

最后，要将RTB的内容设置为当前选项卡页中的组合体之一，需要处理TabChanged事件的tabControl。

 private void tabControl1_Selected(object sender, TabControlEventArgs e) 
     switch(e.TabPageIndex)
         case 0:
            richTextBox.Text = comboBox1.Text;            
            break;
         // so on for the other page and combos
 }

或者，如果您的组合框共享其名称的一个共同的初始部分

 private void tabControl1_Selected(object sender, TabControlEventArgs e) 
    var result = e.TabPage.Controls.OfType<ComboBox>()
                .Where(x => x.Name.StartsWith("cboFunction"));