Setting dates on X axis - vba

Question

I'm trying to create a chart in Excel VBA and am having problems getting the X-Axis to display the dates correctly; the code is below:
Function CreateChart()
Dim objChart As Chart
ReDim detached_price(detachedProps.count - 1) As Double
ReDim detached_date(detachedProps.count - 1) As Date
ReDim semi_price(semiProps.count - 1) As Double
ReDim semi_date(semiProps.count - 1) As Date
Dim minDate As Date
Dim maxDate As Date
minDate = Date
Dim detachedCount As Integer
detachedCount = 0
Dim semiCount As Integer
semiCount = 0
Set objChart = Charts.Add
With objChart
.HasTitle = True
.ChartTitle.Characters.Text = "Price Paid"
.ChartType = xlXYScatter
.Location xlLocationAsNewSheet
.Axes(xlCategory, xlPrimary).HasTitle = True
.Axes(xlCategory, xlPrimary).AxisTitle.Characters.Text = "Date"
.Axes(xlCategory, xlPrimary).CategoryType = xlTimeScale
.Axes(xlCategory, xlPrimary).TickLabels.NumberFormat = "yyyy"
.Axes(xlCategory, xlPrimary).MinimumScaleIsAuto = True
.Axes(xlCategory, xlPrimary).MaximumScaleIsAuto = True
For Each prop In properties
Select Case prop.PropertyType
Case "Detached"
detached_price(detachedCount) = prop.Amount
detached_date(detachedCount) = prop.SellDate
detachedCount = detachedCount + 1
Case "Semi-detached"
semi_price(semiCount) = prop.Amount
semi_date(semiCount) = prop.SellDate
semiCount = semiCount + 1
End Select
If prop.SellDate < minDate Then
minDate = prop.SellDate
End If
If prop.SellDate > maxDate Then
maxDate = prop.SellDate
End If
Next
.SeriesCollection.NewSeries
.SeriesCollection(DETACHED).Name = "Detached"
.SeriesCollection(DETACHED).Values = detached_price
.SeriesCollection(DETACHED).XValues = detached_date
.SeriesCollection.NewSeries
.SeriesCollection(SEMI).Name = "Semi-Detached"
.SeriesCollection(SEMI).Values = semi_price
.SeriesCollection(SEMI).XValues = semi_date
End With End Function
The properties variable in the For..Each loop is populated, and fills the arrays correctly.
However, although the Scatter Graph data points are shown, the dates on the axis all show 1900.
I tried adding the lines:
.Axes(xlCategory, xlPrimary).MinimumScale = CDbl(minDate)
.Axes(xlCategory, xlPrimary).MaximumScale = CDbl(maxDate)
Which showed the correct years along the axis, but now all the data points for both series have disappeared.
I've tried a few other things, but it's been purely on a trial and error basis.
The data is as follows
The resulting charts are:
Correct dates, no data points
Incorrect dates, but we have data points

Answer 1

Even though I disagree with their definition of "common" date format :q, I think that #chiliNUT is on to something. There seems to be some problem with the coercion of the date format.
If you change all of your Date type variables to Double or Long, it should work.
For example change
ReDim detached_date(detachedProps.count - 1) As Date
to
ReDim detached_date(detachedProps.count - 1) As Double
or
ReDim detached_date(detachedProps.count - 1) As Long
This way the dates are not converted into String by the XValues method. They are stored as date serial numbers and the axis routine is able to coerce them successfully into the local date format.
Whats happening in your code is the Date types are coerced to String by the XValues method and the axis rendering routine seems to be unable to coerce them back into dates properly.
I don't think it is actually related to the international settings as I tried it using dates like this:
1/01/2013
1/01/2014
1/01/2015
1/01/2016
1/01/2017
1/01/2018
1/01/2019
1/01/2020
1/01/2021
which works in either system.
I think its just a bug in the axis rendering routine where its unable to properly coerce strings into dates.
I would be interested to hear from others more knowledgeable than me.
Also, I'm curious about this:
.SeriesCollection.NewSeries
.SeriesCollection(DETACHED).Name = "Detached"
.SeriesCollection(DETACHED).Values = detached_price
.SeriesCollection(DETACHED).XValues = detached_date
How does it know which series to reference? Is DETACHED a constant you have defined elsewhere?
I would think this would be better:
with objChart.SeriesCollection.NewSeries
.Name = "Detached"
.Values = detached_price
.XValues = detached_date
end with