combobox总是选中下拉表中的第一条，怎么让他不选中任何项？

[cloud1121]

如上

[microggmy]

combobox.Text="";

[saucer]

Combobox1.SelectedIndex = -1;

[cloud1121]

这两个方法都试了还是不行啊。代码：
private void intl()
{
DataView r_1=code.dv("select ysh from ysb");
comboBox1.DataSource=r_1;
comboBox1.DisplayMember="ysh";
comboBox1.ValueMember="ysh";
DataView r_2=code.dv("select fjh from fjxx where fjh not in (select fjh from ysb where fjh<>'')");
comboBox2.DataSource=r_2;
comboBox2.DisplayMember="fjh";
comboBox2.ValueMember="fjh";
textBox1.Text=code.getdate(3);
textBox2.Text=code.getdate(3);
comboBox1.Focus();
}

private void khdj_Load(object sender, System.EventArgs e)
{
intl();
textBox3.Text="";
comboBox1.Text="";
comboBox1.SelectedIndex=-1;
}

[saucer]

try

combobox1.SelectedItem = null;
combobox1.SelectedIndex = -1;

[cloud1121]

虽然还是不行，但给分了。