C# Combobox清空值

C#combobox1中设置dropdownstyle为dropdownlist，清空时写法： comboBox1.SelectedIndex = -1;

C#combobox1中设置dropdownstyle为dropdown，清空时写法： comboBox1.text= "";

C#combobox1中设置了items，清空items时写法： comboBox2.Items.Clear();