//1.this.dataGridView1.DataSource = null;//会将DataGridView的列也删掉

//2.this.dataGridView1.Columns.Clear(); //异常

//3.重新绑定之前的DataTable,然后清除DataTable中的数据完美解决

  DataTable  dt  =  (DataTable)dataGridView1.DataSource;

  dt.Rows.Clear();

  dataGridView1.DataSource  =  dt;