C# DataGrid ContextMenuOpening error if I click on empty space-CodePudding

first of all, I'm learning so please don't take it hard on me, please. I have a DataGrid that takes data from the database and I want to add ContextMenu which takes the first column (Id) so I can use the delete action on the database. I search a little and end up by this codes:

For adding ConextMenu XML

<DataGrid.ContextMenu>
    <ContextMenu>
      <MenuItem Header="delete" Click="BtnFactorDell">
         <MenuItem.Icon>
           <Image Width="12" Height="12" Source="img/delete.png"/>
         </MenuItem.Icon>
    </ContextMenu>
 </DataGrid.ContextMenu>

and for chosing the first colomn which is my id i use this:

string factorselectedid;
private void FactorGrid_ContextMenuOpening(object sender, ContextMenuEventArgs e)
    {

        object item = FactorGrid.SelectedItem;
        factorselectedid = (FactorGrid.SelectedCells[0].Column.GetCellContent(item) as TextBlock).Text;
    }

Now I have 1 problem and 1 question, first about the question is what is that TextBlock at the end? because it was TexBox in the codes I found by searching and I get some errors so I randomly change it to TextBlock and it works fine! now I'm confused about what is this.

And about my problem is when I click on empty space on the DataGridview it gives me the error:

System.ArgumentOutOfRangeException: 'Specified argument was out of the range of valid values. Parameter name: index'

on the line

factorselectedid = (FactorGrid.SelectedCells[0].Column.GetCellContent(item) as TextBlock).Text;

What can I do to only work if I click on the files not empty space of my Datagrid? Thank You.

CodePudding user response：

what is that TextBlock at the end?

GetCellContent(item) returns a FrameworkElement, but a FrameworkElement doesn't have a Text property. In your case the thing that is returned is a (derivative of) a TextBlock which is a FrameworkElement (TextBlock derives from FrameworkElement), but to access the Text property you have to cast the returned FrameworkElement to a TextBlock first

You might well have seen examples that cast to TextBox; those examples would work if the thing being cast was actually a TextBox - in your case it's not a TextBox but it is a TextBlock (or something else that derives from TextBlock), so a cast to TextBlock works OK.

System.ArgumentOutOfRangeException: 'Specified argument was out of the range of valid values. Parameter name: index'

You just straight attempt to access the first cell ([0]) in SelectedCells without really knowing if there are any selected cells at all; if there are no selected cells, you'll hit a problem

Consider instead to check if there is at least 1 cell before trying to access is:

if(FactorGrid.SelectedCells.Count > 0)
  factorselectedid = (FactorGrid.SelectedCells[0].Column.GetCellContent(item) as TextBlock)?.Text;
else
  e.Handled = true; //suppress the context menu from opening at all

I've also added ? before .Text - it will prevent a crash if the thing is ever not a TextBlock, but it will mean that factorselectedid ends up null. Any code that uses factorselectedid should perhaps check it for being null first