dataTable.Clear中的NullReferenceException

Question

任何人都知道为什么行FullNameTextBox.Text = row [0] .ToString（）;每当调用dataTable.Clear（）时都会导致NullReferenceException？因为这个我不能使用TableAdapter.Fill（）。 ta.Insert可以正常工作，直到您单击数据网格上的行。将FullNameTextBox更改为不在ta.Insert行中的另一个文本框也不起作用。

    private DataRowView row;
    private byte[] xByte;
    TestDataSetTableAdapters.TestingTableTableAdapter ta = new TestDataSetTableAdapters.TestingTableTableAdapter();
    TestDataSet ts = new TestDataSet();

    private void AddButton_Click(object sender, RoutedEventArgs e)
    {
        ta.Insert(FullNameTextBox.Text, xByte, ColumnTwoTextBox.Text, ColumnThreeTextBox.Text);
        ta.Fill(ts.TestingTable);
    }

    private void TestGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        row = (DataRowView)TestGrid.SelectedItem;
        FullNameTextBox.Text = row[0].ToString(); //this would cause the exception removing this line would make the Add Button work even when the SelectionChanged event has been triggered
    }