向Panel添加UserControl

private void button1_Click(object sender, EventArgs e)
{
    panel1.Controls.Clear();
    WebBrowser wb = new WebBrowser();
    wb.Dock = DockStyle.Fill;
    panel1.Controls.Add(wb);
}

private void button2_Click(object sender, EventArgs e)
{
    //GC.Collect();
    panel1.Controls.Clear();
    UC uc = new UC();
    uc.Dock = DockStyle.Fill;
    panel1.Controls.Add(uc);
}