数据集中的图表显示问题到具有多个系列的图表答案

【问题标题】：Chart display issue in dataset to chart with multiple series数据集中的图表显示问题到具有多个系列的图表
【发布时间】：2015-06-08 20:08:07
【问题描述】：

图表新手，这是我第一次尝试，所以就这样吧。我根据Separating Chart Series 中给出的答案构建了我的代码

我正在使用的图表仅经过修改以添加系列 2-7，并将系列类型从条形更改为样条给定的所有系列。所述更改通过 GUI 进行。

执行时，数据集被正确检索，图表关键区域中的系列名称更新并正常显示，但图表本身不显示，除了右侧的颜色键外，仍然是一个空白框。

数据类型：DateTime = DateTime，MCEC & AECC = Decimal，所有其他 = 整数

编辑：

第 2 天：尝试（多次）不同的代码尝试，最近一次是每次更新图表时擦除并重新建立系列（通过屏幕上的组合框），没有变化。
第 3 天：
- 更多替代代码尝试，最新迭代如下所示
- 尝试删除和添加新图表（完全未修改）
第 14 天：
- 自上次编辑以来已尝试了大约 30 种不同的变体，但仍然没有成功。
- 已经获得了我认识的开发人员的帮助，尝试了他的代码变体（如下），但我们都遇到了困难。变体代码有一对要显示的图表，但上面没有显示系列。在这一点上，我正在寻找一个插件，希望能完成这项工作。

第 14 天代码：

Private Sub T3UpdateDisplay()
    '/////////////////////////////////
    'Query database and display results in the chart
    '/////////////////////////////////
    'build sql for processing
    sql = "SELECT DateTime, AECCRate1 AS AECC, MCECRate1 AS MCEC, Manila, Gosnell, Lepanto, Reginold, Promised_Land " _
     & "FROM pt_demand WHERE DateTime BETWEEN '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "' " _
     & "ORDER BY DateTime ASC;"

    SetUpChart()
    GetAllDemands()

End Sub

Private Sub SetUpChart()

    Chart1.Series.Clear()
    Chart1.ChartAreas.Clear()

    Chart1.Series.Add("AECC")
    Chart1.ChartAreas.Add("AD")
    Chart1.Series("AECC").ChartArea = "AD"

    Chart1.Series.Add("MCEC")
    Chart1.ChartAreas.Add("MD")
    Chart1.Series("MCEC").ChartArea = "MD"

    Chart1.Series.Add("Manila")
    Chart1.ChartAreas.Add("M")
    Chart1.Series("Manila").ChartArea = "M"

    Chart1.Series.Add("Gosnell")
    Chart1.ChartAreas.Add("G")
    Chart1.Series("Gosnell").ChartArea = "G"

    Chart1.Series.Add("Lepanto")
    Chart1.ChartAreas.Add("L")
    Chart1.Series("Lepanto").ChartArea = "L"

    Chart1.Series.Add("Reginold")
    Chart1.ChartAreas.Add("R")
    Chart1.Series("Reginold").ChartArea = "R"

    Chart1.Series.Add("PromisedLand")
    Chart1.ChartAreas.Add("P")
    Chart1.Series("PromisedLand").ChartArea = "P"

    Chart1.Series("AECC").Color = Color.Green
    Chart1.Series("MCEC").Color = Color.Blue
    Chart1.Series("Manila").Color = Color.Red
    Chart1.Series("Gosnell").Color = Color.Gray
    Chart1.Series("Lepanto").Color = Color.Purple
    Chart1.Series("Reginold").Color = Color.Orange
    Chart1.Series("PromisedLand").Color = Color.Yellow

    Chart1.Series("AECC").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("MCEC").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("Manila").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("Gosnell").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("Lepanto").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("Reginold").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
    Chart1.Series("PromisedLand").ChartType = DataVisualization.Charting.SeriesChartType.FastLine

    Chart1.Series("AECC").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("MCEC").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("Manila").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("Gosnell").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("Lepanto").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("Reginold").XValueType = DataVisualization.Charting.ChartValueType.Time
    Chart1.Series("PromisedLand").XValueType = DataVisualization.Charting.ChartValueType.Time

End Sub

Private Sub GetAllDemands()
    'Connect to database do SQL for Dates Between
    On Error GoTo Err_Control
    Dim myDBCS As String = Main.DBCS    'create local copy of database connection string
    Dim ThisRecKey As Guid
    Dim sqlConnectionString As String = myDBCS

    Dim strGetDemandsSQL As String = sql
    Using sConnection As New SqlConnection(sqlConnectionString)
        sConnection.Open()
        Dim GetRecKeySQLCommand As New SqlCommand(strGetDemandsSQL, sConnection)
        'Get the Rec_Key
        Dim reader As SqlDataReader = GetRecKeySQLCommand.ExecuteReader()
        Dim ThisDateTime As Date

        While reader.Read()
            'Add Points
            Debug.Print(reader(0) & "    " & reader(1) & "    " & reader(2) & "    " & reader(3) & "    " & reader(4) & "    " & reader(5) & "    " & reader(6) & "    " & reader(7))
            ThisDateTime = reader(0)
            Chart1.Series("AECC").Points.AddXY(ThisDateTime.ToOADate(), CDbl(reader(1)))
            Chart1.Series("MCEC").Points.AddXY(ThisDateTime.ToOADate(), CDbl(reader(2)))
            Chart1.Series("M").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(3)))
            Chart1.Series("G").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(4)))
            Chart1.Series("L").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(5)))
            Chart1.Series("R").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(6)))
            Chart1.Series("P").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(7)))

        End While
        reader.Close()
        sConnection.Close()
    End Using

    Dim dblMin, dblMax As Double
    SetMinMax(dblMin, dblMax, "AECCRate1")
    Chart1.ChartAreas("AD").AxisY.Minimum = dblMin
    Chart1.ChartAreas("AD").AxisY.Maximum = dblMax
    Chart1.ChartAreas("AD").AxisX.Title = "AECC: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "MCECRate1")
    Chart1.ChartAreas("MD").AxisY.Minimum = dblMin
    Chart1.ChartAreas("MD").AxisY.Maximum = dblMax
    Chart1.ChartAreas("MD").AxisX.Title = "MCEC: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "Manila")
    Chart1.ChartAreas("M").AxisY.Minimum = dblMin
    Chart1.ChartAreas("M").AxisY.Maximum = dblMax
    Chart1.ChartAreas("M").AxisX.Title = "Manila: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "Gosnell")
    Chart1.ChartAreas("G").AxisY.Minimum = dblMin
    Chart1.ChartAreas("G").AxisY.Maximum = dblMax
    Chart1.ChartAreas("G").AxisX.Title = "Gosnell: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "Lepanto")
    Chart1.ChartAreas("L").AxisY.Minimum = dblMin
    Chart1.ChartAreas("L").AxisY.Maximum = dblMax
    Chart1.ChartAreas("L").AxisX.Title = "Lepanto: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "Reginold")
    Chart1.ChartAreas("R").AxisY.Minimum = dblMin
    Chart1.ChartAreas("R").AxisY.Maximum = dblMax
    Chart1.ChartAreas("R").AxisX.Title = "Reginold: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

    SetMinMax(dblMin, dblMax, "Promised_Land")
    Chart1.ChartAreas("P").AxisY.Minimum = dblMin
    Chart1.ChartAreas("P").AxisY.Maximum = dblMax
    Chart1.ChartAreas("P").AxisX.Title = "Promised Land: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

Exit_Here:

    Exit Sub
Err_Control:
    Select Case Err.Number
        Case Else
            Resume Exit_Here
    End Select
End Sub

Private Sub SetMinMax(ByRef Min As Double, ByRef Max As Double, FieldName As String)
    On Error GoTo Err_Control
    Dim myDBCS As String = Main.DBCS    'create local copy of database connection string
    Dim sqlConnectionString As String = myDBCS
    Dim strGetMaxSQL As String = "Select MAX(" & FieldName & ") FROM pt_demand WHERE DateTime Between '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "'"
    Dim strGetMinSQL As String = "Select MIN(" & FieldName & ") FROM pt_demand WHERE DateTime Between '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "'"
    Using sConnection As New SqlConnection(sqlConnectionString)
        sConnection.Open()
        'MAX
        Dim GetMaxSQLCommand As New SqlCommand(strGetMaxSQL, sConnection)
        Dim readerMax As SqlDataReader = GetMaxSQLCommand.ExecuteReader()

        While readerMax.Read()
            Max = CDbl(CInt(readerMax(0) + (0.01 * readerMax(0))))
        End While
        readerMax.Close()
        'MIN
        Dim GetMinSQLCommand As New SqlCommand(strGetMinSQL, sConnection)
        'Get the Rec_Key
        Dim readerMin As SqlDataReader = GetMinSQLCommand.ExecuteReader()

        While readerMin.Read()
            Min = CDbl(CInt(readerMin(0) - (0.01 * readerMin(0))))
        End While
        readerMin.Close()

        sConnection.Close()
    End Using

Exit_Here:

    Exit Sub
Err_Control:
    Select Case Err.Number
        Case Else
            Resume Exit_Here
    End Select
End Sub

第 3 天代码在这里：

Private Sub T3UpdateDisplay()
            '/////////////////////////////////
    'Query database and display results in the chart
    '  borrowed from https://stackoverflow.com/questions/22638639/separating-chart-series
    '/////////////////////////////////
    'build sql for processing
    sql = "SELECT DateTime, MCECRate1 AS MCEC, AECCRate1 AS AECC, Manila, Gosnell, Lepanto, Reginold, Promised_Land " _
     & "FROM pt_demand WHERE DateTime BETWEEN '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "' " _
     & "ORDER BY DateTime ASC;"

    '---- REMOVE FROM PRODUCTION ----
    'Main.Msg2User(sql, "query")

    Using ds = dbSelect_DataSet(sql)
        Chart1.Series.Clear()       'dump all series and recreate
        Chart1.Titles.Clear()       'dump title for recreation later

        Chart1.Titles.Add("System Demands: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm"))

        Dim mcec As New Series()
        mcec.ChartArea = "ChartArea1"
        mcec.Name = "MCEC"
        Chart1.Series.Add(mcec)
        Chart1.Series(mcec.Name).Color = Color.Green
        Chart1.Series(mcec.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(mcec.Name).XValueMember = "DateTime"
        Chart1.Series(mcec.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(mcec.Name).YValueMembers = "MCEC"
        Chart1.Series(mcec.Name).YValueType = ChartValueType.Double

        Dim aecc As New Series()
        aecc.ChartArea = "ChartArea1"
        aecc.Name = "AECC"
        Chart1.Series.Add(aecc)
        Chart1.Series(aecc.Name).Color = Color.DarkGray
        Chart1.Series(aecc.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(aecc.Name).XValueMember = "DateTime"
        Chart1.Series(aecc.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(aecc.Name).YValueMembers = "AECC"
        Chart1.Series(aecc.Name).YValueType = ChartValueType.Double

        Dim m As New Series()
        m.ChartArea = "ChartArea1"
        m.Name = "Manila"
        Chart1.Series.Add(m)
        Chart1.Series(m.Name).Color = Color.Blue
        Chart1.Series(m.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(m.Name).XValueMember = "DateTime"
        Chart1.Series(m.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(m.Name).YValueMembers = "Manila"
        Chart1.Series(m.Name).YValueType = ChartValueType.Int32

        Dim g As New Series()
        g.ChartArea = "ChartArea1"
        g.Name = "Gosnell"
        Chart1.Series.Add(g)
        Chart1.Series(g.Name).Color = Color.Gold
        Chart1.Series(g.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(g.Name).XValueMember = "DateTime"
        Chart1.Series(g.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(g.Name).YValueMembers = "Gosnell"
        Chart1.Series(g.Name).YValueType = ChartValueType.Int32

        Dim l As New Series()
        l.ChartArea = "ChartArea1"
        l.Name = "Lepanto"
        Chart1.Series.Add(l)
        Chart1.Series(l.Name).Color = Color.Red
        Chart1.Series(l.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(l.Name).XValueMember = "DateTime"
        Chart1.Series(l.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(l.Name).YValueMembers = "Lepanto"
        Chart1.Series(l.Name).YValueType = ChartValueType.Int32

        Dim r As New Series()
        r.ChartArea = "ChartArea1"
        r.Name = "Reginold"
        Chart1.Series.Add(r)
        Chart1.Series(r.Name).Color = Color.Orange
        Chart1.Series(r.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(r.Name).XValueMember = "DateTime"
        Chart1.Series(r.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(r.Name).YValueMembers = "Reginold"
        Chart1.Series(r.Name).YValueType = ChartValueType.Int32

        Dim p As New Series()
        p.ChartArea = "ChartArea1"
        p.Name = "Promised Land"
        Chart1.Series.Add(p)
        Chart1.Series(p.Name).Color = Color.Purple
        Chart1.Series(p.Name).ChartType = SeriesChartType.Spline
        Chart1.Series(p.Name).XValueMember = "DateTime"
        Chart1.Series(p.Name).XValueType = ChartValueType.DateTime
        Chart1.Series(p.Name).YValueMembers = "Promised_Land"
        Chart1.Series(p.Name).YValueType = ChartValueType.Int32

        Chart1.Size = New System.Drawing.Size(973, 467)
        'Chart1.BackColor = Color.WhiteSmoke
        Chart1.ChartAreas(0).AxisX.LabelStyle.Format = "MM/dd HH:mm"

        Chart1.DataSource = ds.Tables("pt_demand")
        Chart1.DataBind()
        Chart1.Visible = True

    End Using

End Sub

【问题讨论】：

标签： vb.net charts dataset series graphing

【解决方案1】：

我仍然不完全确定为什么它在我尝试的前几次不起作用，但我怀疑次要数据类型差异之间可能存在问题（前两个系列是十进制，其余的是整数）。

最终的解决方案（以下是精简代码）是为两种不同类型的数据生成两个不同的图表，将图表保存到用户配置文件目录中的 png 文件中，敲出一个 html 文件来处理最终的格式化、显示和打印需要，然后以编程方式打开文件。

以下示例代码仅包括：

Chart2 的生成，因为它是两个图表中更复杂的一个
适当设置图表 y 轴的过程，以及

将图表保存到磁盘的过程。

Imports System.Windows.Forms.DataVisualization.Charting
Imports System.IO

... ... ...

Dim myDBCS As String = Main.DBCS    'create local copy of database connection string
Dim myAPPFOLDER As String = Main.APPFOLDER  'local copy of scratchpad folder
Dim ReportStart, ReportEnd As DateTime  'reporting dates, persistent
Dim dblMin, dblMax As Double    'minimum and maximum values for y axis settings
Dim sql As String   'holds sql for construction & execute
Dim Chart1 As New Chart 'rate1 chart
Dim Chart2 As New Chart 'subs chart

... ... ...

Public Sub PTRSubs()
'/////////////////////////////////
'Build & execute SQL Query, Parse results, build chart
'/////////////////////////////////

'build sql
Dim cols As String = ""
sql = "SELECT DateTime, Gosnell, Lepanto, Manila, Reginold " _
  & "FROM pt_demand WHERE DateTime BETWEEN '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString _
  & "' ORDER BY DateTime ASC;"

'/////////////////////////////////
'Setup Chart2
'if we're talking more than 1 day's worth of data, change the x axis type to datetime, otherwise, leave as time
Dim x As Boolean
If DateDiff(DateInterval.Day, ReportStart, ReportEnd) > 1 Then
    x = True
Else
    x = False
End If

Chart2.Size = New System.Drawing.Size(1280, 575)
Chart2.Series.Clear()
Chart2.ChartAreas.Clear()

Chart2.ChartAreas.Add("Subs")

'/////////////////////////////////
'define series parameters
Chart2.Series.Add("Gosnell")
Chart2.Series("Gosnell").ChartArea = "Subs"
Chart2.Series("Gosnell").Color = Color.Gray
Chart2.Series("Gosnell").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
Chart2.Series("Gosnell").XValueType = DataVisualization.Charting.ChartValueType.Time
If x = True Then
    Chart2.Series("Gosnell").XValueType = DataVisualization.Charting.ChartValueType.DateTime
Else
    Chart2.Series("Gosnell").XValueType = DataVisualization.Charting.ChartValueType.Time
End If

Chart2.Series.Add("Lepanto")
Chart2.Series("Lepanto").ChartArea = "Subs"
Chart2.Series("Lepanto").Color = Color.Purple
Chart2.Series("Lepanto").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
Chart2.Series("Lepanto").XValueType = DataVisualization.Charting.ChartValueType.Time
If x = True Then
    Chart2.Series("Lepanto").XValueType = DataVisualization.Charting.ChartValueType.DateTime
Else
    Chart2.Series("Lepanto").XValueType = DataVisualization.Charting.ChartValueType.Time
End If

Chart2.Series.Add("Manila")
Chart2.Series("Manila").ChartArea = "Subs"
Chart2.Series("Manila").Color = Color.Red
Chart2.Series("Manila").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
Chart2.Series("Manila").XValueType = DataVisualization.Charting.ChartValueType.Time
If x = True Then
    Chart2.Series("Manila").XValueType = DataVisualization.Charting.ChartValueType.DateTime
Else
    Chart2.Series("Manila").XValueType = DataVisualization.Charting.ChartValueType.Time
End If

Chart2.Series.Add("Reginold")
Chart2.Series("Reginold").ChartArea = "Subs"
Chart2.Series("Reginold").Color = Color.Orange
Chart2.Series("Reginold").ChartType = DataVisualization.Charting.SeriesChartType.FastLine
Chart2.Series("Reginold").XValueType = DataVisualization.Charting.ChartValueType.Time
If x = True Then
    Chart2.Series("Reginold").XValueType = DataVisualization.Charting.ChartValueType.DateTime
Else
    Chart2.Series("Reginold").XValueType = DataVisualization.Charting.ChartValueType.Time
End If

'/////////////////////////////////
'Connect to database, execute query
On Error GoTo Err_Control
Dim ThisRecKey As Guid
Dim strGetDemandsSQL As String = sql
Using sConnection As New SqlConnection(myDBCS)
    sConnection.Open()
    Dim GetRecKeySQLCommand As New SqlCommand(strGetDemandsSQL, sConnection)
    'Get the Rec_Key
    Dim reader As SqlDataReader = GetRecKeySQLCommand.ExecuteReader()
    Dim ThisDateTime As Date

    '/////////////////////////////////
    'build series datapoints
    While reader.Read()
        'Add Points
        Debug.Print(reader(0) & "    " & reader(1) & "    " & reader(2) & "    " & reader(3) & "    " & reader(4))
        ThisDateTime = reader(0)

        Chart2.Series("Gosnell").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(1)))
        Chart2.Series("Lepanto").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(2)))
        Chart2.Series("Manila").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(3)))
        Chart2.Series("Reginold").Points.AddXY(ThisDateTime.ToOADate(), CInt(reader(4)))

    End While
    reader.Close()
    sConnection.Close()
End Using

dblMin = 0
dblMax = 0

SetMinMax(dblMin, dblMax, "Gosnell")
If dblMax = 0 Then          'if axis min/max is not already set, then set both min and max based on these values them based on these values
    Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin
    Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax

Else
    If dblMin < Chart2.ChartAreas("Subs").AxisY.Minimum Then Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin 'only reset if value is lower than current setting
    If dblMax > Chart2.ChartAreas("Subs").AxisY.Maximum Then Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax 'only reset if value is higher than current setting

End If

SetMinMax(dblMin, dblMax, "Lepanto")
If dblMax = 0 Then          'if axis min/max is not already set, then set both min and max based on these values them based on these values
    Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin
    Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax

Else
    If dblMin < Chart2.ChartAreas("Subs").AxisY.Minimum Then Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin 'only reset if value is lower than current setting
    If dblMax > Chart2.ChartAreas("Subs").AxisY.Maximum Then Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax 'only reset if value is higher than current setting

End If

SetMinMax(dblMin, dblMax, "Manila")
If dblMax = 0 Then          'if axis min/max is not already set, then set both min and max based on these values them based on these values
    Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin
    Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax

Else
    If dblMin < Chart2.ChartAreas("Subs").AxisY.Minimum Then Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin 'only reset if value is lower than current setting
    If dblMax > Chart2.ChartAreas("Subs").AxisY.Maximum Then Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax 'only reset if value is higher than current setting

End If

SetMinMax(dblMin, dblMax, "Reginold")
If dblMax = 0 Then          'if axis min/max is not already set, then set both min and max based on these values them based on these values
    Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin
    Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax

Else
    If dblMin < Chart2.ChartAreas("Subs").AxisY.Minimum Then Chart2.ChartAreas("Subs").AxisY.Minimum = dblMin 'only reset if value is lower than current setting
    If dblMax > Chart2.ChartAreas("Subs").AxisY.Maximum Then Chart2.ChartAreas("Subs").AxisY.Maximum = dblMax 'only reset if value is higher than current setting

End If

'/////////////////////////////////
'set axis title
Chart2.ChartAreas("Subs").AxisX.Title = "Report window: " & Format(ReportStart, "yyyy/MM/dd HH:mm") & " to " & Format(ReportEnd, "yyyy/MM/dd HH:mm")

DumpChartToImage(Chart2, "Chart2")

Exit_Here:
Exit Sub

Err_Control:
Select Case Err.Number
    Case Else
        MsgBox("PTRSubs" & vbCrLf _
         & "Error Number: " & Err.Number.ToString & vbCrLf _
         & "Description:  " & Err.Description.ToString & vbCrLf _
         & "Source:  " & Err.Source, MsgBoxStyle.OkOnly, "errcontrol")
        Resume Exit_Here
End Select
End Sub

Private Sub SetMinMax(ByRef Min As Double, ByRef Max As Double, FieldName As String)
'/////////////////////////////////
'Get min and Max values of data from selected set
'/////////////////////////////////

On Error GoTo Err_Control

Dim strGetMaxSQL As String = "Select MAX(" & FieldName & ") FROM pt_demand WHERE DateTime Between '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "'"
Dim strGetMinSQL As String = "Select MIN(" & FieldName & ") FROM pt_demand WHERE DateTime Between '" & ReportStart.ToString & "' AND '" & ReportEnd.ToString & "'"
Using sConnection As New SqlConnection(myDBCS)
    sConnection.Open()
    'MAX
    Dim GetMaxSQLCommand As New SqlCommand(strGetMaxSQL, sConnection)
    Dim readerMax As SqlDataReader = GetMaxSQLCommand.ExecuteReader()

    While readerMax.Read()
        Max = CDbl(CInt(readerMax(0) + (0.01 * readerMax(0))))
    End While
    readerMax.Close()
    'MIN
    Dim GetMinSQLCommand As New SqlCommand(strGetMinSQL, sConnection)
    'Get the Rec_Key
    Dim readerMin As SqlDataReader = GetMinSQLCommand.ExecuteReader()

    While readerMin.Read()
        Min = CDbl(CInt(readerMin(0) - (0.01 * readerMin(0))))
    End While
    readerMin.Close()

    sConnection.Close()
End Using

Exit_Here:
Exit Sub

Err_Control:
Select Case Err.Number
    Case Else
        Resume Exit_Here
End Select
End Sub

Private Sub DumpChartToImage(ByRef mychart As Chart, ByRef file As String)
'//////////////////////
'Save chart to file on disk, first wipe old copy if already exists
'//////////////////////
Dim filename As String = myAPPFOLDER & file & ".png"
If System.IO.File.Exists(filename) Then
    'The file exists, delete it first
    System.IO.File.Delete(filename)
    'recreate the file
    mychart.SaveImage(filename, System.Drawing.Imaging.ImageFormat.Png)

Else
    'the file doesn't exist, create it
    mychart.SaveImage(filename, System.Drawing.Imaging.ImageFormat.Png)

End If

End Sub

【讨论】：