Right way to change datagrid row, column, cells background colors in code-behind?

Question

Hi all,
I have a winform program that I'm upgrading to wpf (I'm new to wpf). The wpf code for the function (SetdataGridBackgroundColors()) is below with the winform code commented out so I can fix it.  I have a datagrid with a Cornsilk background color alteranating
with LightGreen depending on the content of datetime  cell. If the day portion of the datetime is different then the color changes from one to the other. I used a colorIndex variable because at the end of the month it could go from 31 to 1 and that would
not work if I use the day directly.
I tried this line to change the background color:
optionsDataDatagrid.RowBackground = new SolidColorBrush(Colors.Cornsilk);
this works but it changes every row. I found this other stuff:
DataGridRow currentRowColor = optionsDataDatagrid.ItemContainerGenerator.ContainerFromIndex(i) as DataGridRow;
//DataGridRow currentRowColor = optionsDataDatagrid.ItemContainerGenerator.ContainerFromItem(optionsDataDatagrid.Items[i]) as DataGridRow;
currentRowColor.Background = new SolidColorBrush(Colors.Cornsilk);
Either ContainerFromIndex or ContainerFromItem throw an exception because currentRowColor is null. I looked at optionsDataDatagrid.Items[i] and is not null. Then I read that using ItemContainerGenerator is not a good idea.
BTW I'm calling SetdataGridBackgroundColors() after datagrid is been filled with data.
So... what is the proper way to set each row, column or cell background color in wpf?
Thanks
private void SetdataGridBackgroundColors()
optionRowData rowData = new optionRowData();
if (optionsDataDatagrid.Items.Count == 0)
return;
int colorIndex = 1;
DateTime savedDate, currentRowDate;
rowData = optionsDataDatagrid.Items[0] as optionRowData;
savedDate = rowData.col_datetime.Date; //only compare the date not the time
for (int i = 0; i < optionsDataDatagrid.Items.Count; i++)
//currentRowDate = Convert.ToDateTime(optionsDataDatagrid.Rows[i].Cells[3].Value); //winform code
//currentRowDate = currentRowDate.Date; //winform code
rowData = optionsDataDatagrid.Items[i] as optionRowData;
currentRowDate = rowData.col_datetime.Date;
if (currentRowDate != savedDate)
colorIndex++;
savedDate = currentRowDate;
if (colorIndex % 2 == 0)
//optionsDataDatagrid.Rows[i].DefaultCellStyle.BackColor = Color.Cornsilk;
//------------------- testing new code --------------begin
optionsDataDatagrid.RowBackground = new SolidColorBrush(Colors.Cornsilk); //this changes all rows
//DataGridRow currentRowColor = optionsDataDatagrid.ItemContainerGenerator.ContainerFromIndex(i) as DataGridRow;
//DataGridRow currentRowColor = optionsDataDatagrid.ItemContainerGenerator.ContainerFromItem(optionsDataDatagrid.Items[i]) as DataGridRow;
//currentRowColor.Background = new SolidColorBrush(Colors.Cornsilk);
//------------------- testing new code --------------end
//optionsDataDatagrid.Columns[4].DefaultCellStyle.BackColor = Color.DarkSalmon;
//optionsDataDatagrid.Columns[5].DefaultCellStyle.BackColor = Color.Aquamarine;
//optionsDataDatagrid.Rows[i].Cells[4].Style.ApplyStyle(optionsDataDataGridView.Columns[4].DefaultCellStyle);
//optionsDataDatagrid.Rows[i].Cells[5].Style.ApplyStyle(optionsDataDataGridView.Columns[5].DefaultCellStyle);
else
//optionsDataDatagrid.Rows[i].DefaultCellStyle.BackColor = Color.LightGreen;
//------------------- testing new code --------------begin
optionsDataDatagrid.RowBackground = new SolidColorBrush(Colors.LightGreen); //this has no effect
//------------------- testing new code --------------end
//optionsDataDatagrid.Columns[4].DefaultCellStyle.BackColor = Color.Coral;
//optionsDataDatagrid.Columns[5].DefaultCellStyle.BackColor = Color.LimeGreen;
//optionsDataDatagrid.Rows[i].Cells[4].Style.ApplyStyle(optionsDataDataGridView.Columns[4].DefaultCellStyle);
//optionsDataDatagrid.Rows[i].Cells[5].Style.ApplyStyle(optionsDataDataGridView.Columns[5].DefaultCellStyle);

Answer 1

I (also) strongly recommend mvvm.
Setting values is a particularly bad idea in this case.
I don't mean to be rude but your explanation of the requirement is kind of vague.
I would bind solidcolourbrushes.
Set the properties based on whatever your logic is within the viewmodel.
You can switch out what each of the brushes holds when the user clicks wherever.
So you use a highlightbrush when something or other is true.
That highlightbrush is set to a blue brush when the user clicks left and a red brush when they click right.
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