我做了一个comboBox联动,现在通过第一个comboBox中的选项,第二个comboBox可以显示相对应的数据,可是再通过第一个comboBox选择的时候,第二个comboBox中的数据是上一次的加上这一次的,怎么可以去掉上一次的数据,每次都显示当前这回选择的?
还有我想在加载的时候出现==请选择==,可是也没显示?
 private void dataExcel_Load(object sender, EventArgs e)
        {
            
            db.RunSQL("select goodsoffer from goodsInfo group by goodsoffer", ref ds, "goodsInfo");
            DataTable dtGroup = ds.Tables["goodsInfo"];
            comboBox1.DataSource = dtGroup;
            comboBox1.DisplayMember = "goodsOffer";

            
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox1.SelectedItem;
                string gId = drv.Row["goodsOffer"].ToString();
                db.RunSQL("select goodsID,goodsBrand from goodsInfo where goodsoffer='" + gId + "'", ref ds, "goodsInfo1");

                DataTable dtUser = ds.Tables["goodsInfo1"];
                comboBox2.DataSource = dtUser;
                comboBox2.DisplayMember = "goodsBrand";
            }
        }

将:
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox1.SelectedItem;
                string gId = drv.Row["goodsOffer"].ToString();
                db.RunSQL("select goodsID,goodsBrand from goodsInfo where goodsoffer='" + gId + "'", ref ds, "goodsInfo1");

                DataTable dtUser = ds.Tables["goodsInfo1"];
                comboBox2.DataSource = dtUser;
                comboBox2.DisplayMember = "goodsBrand";
            }
        }
改为:
       private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            DataTable dtUser=null;
            comboBox2.DataSource = dtUser;

            if (comboBox1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox1.SelectedItem;
                string gId = drv.Row["goodsOffer"].ToString();
                db.RunSQL("select goodsID,goodsBrand from goodsInfo where goodsoffer='" + gId + "'", ref ds, "goodsInfo1");

                dtUser = ds.Tables["goodsInfo1"];
                comboBox2.DataSource = dtUser;
                comboBox2.DisplayMember = "goodsBrand";
            }
        }

你测试一下

不行的话,再改为以下试试:
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            DataTable dtUser=New DataTable();
            comboBox2.DataSource = dtUser;

            if (comboBox1.SelectedIndex > -1)
            {
                DataRowView drv = (DataRowView)comboBox1.SelectedItem;
                string gId = drv.Row["goodsOffer"].ToString();
                db.RunSQL("select goodsID,goodsBrand from goodsInfo where goodsoffer='" + gId + "'", ref ds, "goodsInfo1");

                dtUser = ds.Tables["goodsInfo1"];
                comboBox2.DataSource = dtUser;
                comboBox2.DisplayMember = "goodsBrand";
            }
        }

感谢hainandgm,清空数据我已经搞定了,我用的是ds.Tables.Remove("goodsInfo1");
现在就差加一个"==请选择=="了