There seems to be issue with the preview. When using the sample program custom preview (FlexCelVCLNT\Demo\Delphi\Modules\25.Printing and Exporting\20.CustomPreview) it works fine for the Charts.template.xls file (FlexCelVCLNT\Demo\Delphi\Modules\20.Reports\70.Charts).
I opened the template file in Excel and saved it as XLSX.
When open the XLSX file in the the custom preview program, the charts are just blank space.
What do I miss? How can I make it work, without reverting to the old XLS files?
The rendering engine currently ony renders xls charts. We are working really hard in rendering xlsx charts and it is kind of working here internally, but there are still a lot of details to polish. Xlsx chart rendering will be the biggest feature in FlexCel 7, which is expected soon.
Sadly I can't give you a date because we are already very late (I wanted to have FlexCel 7 for december 2018, but there is just too much weird stuff in the way Excel renders the charts and we want everything to work right). But we are trying to have this as soon as we can.
Until you will have FlexCel7 ready, I can go back to XLS. At least for the preview. Can I somehow convert a XLS file to XLSX with the current FlexCel? If so, where can I find code that does that?
But sadly FlexCel will not convert the charts between xls<->xlsx. If it could do that, then it could also be able to render xlsx charts. And sadly due to the big differences between both charts formats (not even Excel does a good job converting them) it is not in our near term plans to implement conversion between xlsx charts and xls charts.