在不搜索整个DataGrid子级的情况下从DataGridTextColumn获取控件

private TextBox GetTextBoxFromDataGridTextColumn(DataGrid dataGrid, int columnIndex)
{
    TextBox textBox = null;
    
    DataGridRow dataGridRow = (DataGridRow)dataGrid.ItemContainerGenerator.ContainerFromIndex(0);
    if (dataGridRow != null)
    {
        DataGridCellsPresenter cellsPresenter = GetVisualChild<DataGridCellsPresenter>(dataGridRow);
        if (cellsPresenter != null)
        {
            DataGridCell dataGridCell = (DataGridCell)cellsPresenter.ItemContainerGenerator.ContainerFromIndex(columnIndex);
            if (dataGridCell != null)
            {
                textBox = GetVisualChild<TextBox>(dataGridCell);
            }
        }
    }
    
    return textBox;
}

private T GetVisualChild<T>(Visual parent) where T : Visual
{
    T child = default(T);
    
    int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
    for (int i = 0; i < numVisuals; i++)
    {
        Visual visual = (Visual)VisualTreeHelper.GetChild(parent, i);
        child = visual as T;
        if (child == null)
        {
            child = GetVisualChild<T>(visual);
        }
        if (child != null)
        {
            break;
        }
    }
    
    return child;
}