B4J Tutorial Read and graph Thingspeak data

In this thread, I explained how to build a weather station with a Wemos mini and an UDP Receiver to show the data. This is great for the present value but to be able to see a trend we need something else. Yes there are apps already for IOS and Android in the stores but what fun is that!

This example uses the chart class from Klaus (included in the Zip file), as well as the libraries: B4XPages, jCore, jFX, jOkHttpUtils2, Json and XUI Views.

Two data sources are included, one is mine and the second is a friend who lives 10 km away. You can add more data sources as required (see line 70 cb1.Items.Add(1050809)).

NOTE: The Thingspeak API will only allow a maximum of 8000 points to be downloaded!

The Code:

B4X:
#Region Shared Files
#CustomBuildAction: folders ready, %WINDIR%\System32\Robocopy.exe,"..\..\Shared Files" "..\Files"
'Ctrl + click to sync files: ide://run?file=%WINDIR%\System32\Robocopy.exe&args=..\..\Shared+Files&args=..\Files&FilesSync=True
#End Region

'Ctrl + click to export as zip: ide://run?File=%B4X%\Zipper.jar&Args=Project.zip

' Examples of requests with json reply
' https://api.thingspeak.com/channels/320990/feeds.json?start=2011-11-11%2010:10:10&end=2011-11-11%2011:11:11
' https://api.thingspeak.com/channels/320990/feeds.json?Days=1
' https://api.thingspeak.com/channels/320990/feeds.json?minutes=60

Sub Class_Globals
    Private Root As B4XView
    Private xui As XUI
    Private LinkURL As String
    Private MyRoot, channel As Map
 
 
 
    Private lbl_Entries As Label
    Private lbl_ID As Label
    Private lbl_last As Label
    Private lbl_Lat As Label
    Private lbl_Lon As Label
    Private lbl_Name As Label
    Private txt_entries As Label
    Private txt_id As Label
    Private txt_lastdate As Label
    Private txt_lasttime As Label
    Private txt_lat As Label
    Private txt_lon As Label
    Private txt_name As Label
    Private lbl_FiledNames As Label
    Private btn1 As Button
    Private btn2 As Button
    Private btn3 As Button
    Private btn4 As Button
    Private btn5 As Button
    Private btn6 As Button
 
    Private SingleLine1 As xChart
    Private ChartTime As List
    Private f1,f2,f3,f4,f5,f6 As List
    Private SortedData As List
    Private btn_day As Button
    Private btn_week As Button
    Private btn_month As Button
    Private btn_max As Button
    Private nResults As Int=96    'start with 1 day
    Private Xdivisions As Int=nResults/10
    Private cb1 As ComboBox
    Dim ChannelNumber As Int=320990
 
 
End Sub

Public Sub Initialize
'    B4XPages.GetManager.LogEvents = True
End Sub

'This event will be called once, before the page becomes visible.
Private Sub B4XPage_Created (Root1 As B4XView)
    Root = Root1
    Root.LoadLayout("MainPage")
    Root.Visible=False
    B4XPages.SetTitle(Me, "Thingspeak Data Viewer")
 
    cb1.Items.Add(320990)
    cb1.Items.Add(1050809)
 
    ' 96 Results/day. 672 Results/week. 2880 Results/month
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
     
    GetData(LinkURL)
End Sub

'You can see the list of page related events in the B4XPagesManager object. The event name is B4XPage.


private Sub GetData(GetLink As String)
    Dim j As HttpJob
    j.Initialize("", Me)
    j.Download(GetLink)
    Wait For (j) JobDone(j As HttpJob)
    If j.Success Then
        Log(j.GetString)
        ParseJSON(j.GetString)
    End If
    j.Release
End Sub

Private Sub ParseJSON(text As String)
    Dim parser As JSONParser
    parser.Initialize(text)
    MyRoot = parser.NextObject
    channel = MyRoot.Get("channel")
 
    txt_id.Text = channel.Get("id")
    txt_entries.Text = channel.Get("last_entry_id")
    txt_lon.Text = channel.Get("longitude")
    txt_lat.Text = channel.Get("latitude")
    txt_name.Text = channel.Get("name")
    'txt_last.Text = channel.Get("updated_at")        this is the last edit date not the last data entry!
 
    btn1.Text = channel.Get("field1")
    btn2.Text = channel.Get("field2")
    btn3.Text = channel.Get("field3")
    btn4.Text = channel.Get("field4")
    btn5.Text = channel.Get("field5")
    btn6.Text = channel.Get("field6")
 
    SortedData.Initialize
    ChartTime.Initialize
    f1.Initialize
    f2.Initialize
    f3.Initialize
    f4.Initialize
    f5.Initialize
    f6.Initialize
 
     
    Dim feeds As List = MyRoot.Get("feeds")
    For Each colfeeds As Map In feeds
        'Dim entry_id As Int = colfeeds.Get("entry_id")
        Dim created_at As String = colfeeds.Get("created_at")
        'Log("Entry numbert: " & entry_id)
     
        'read data fo each field
        Dim field1, field2, field3, field4, field5, field6 As Double
     
        ' Trying to read a NAN into a double will cause a crash, hence Try
        Try
            field1=colfeeds.Get("field1")              
        Catch
            field1=0
        End Try
     
        Try
            field2=colfeeds.Get("field2")
        Catch
            field2=0
        End Try
     
        Try
            field3=colfeeds.Get("field3")
        Catch
            field3=0
        End Try
     
        Try
            field4=colfeeds.Get("field4")
        Catch
            field4=0
        End Try
     
        Try
            field5=colfeeds.Get("field5")
        Catch
            field5=0
        End Try
     
        Try
            field6=colfeeds.Get("field6")
        Catch
            field6=0
        End Try
     
             
        txt_lastdate.Text=created_at.SubString2(0,10)
        txt_lasttime.Text=ConverttoMEZ(created_at.SubString2(11,19))    ' Time is UTC format and we need MEZ
        ChartTime.Add(txt_lastdate.Text & " " & txt_lasttime.Text)
     
        If field1<>0 And field2<>0 And field3<>0 And field4<>0 And field5<>0 And field6<>0 Then
            f1.Add(field1)
            f2.Add(field2)
            f3.Add(field3)
            f4.Add(field4)
            f5.Add(field5)
            f6.Add(field6)        
        Else
            ' If all fileds were 0 then the value is NAN. Add previous value again
            f1.Add(f1.Get(f1.Size-1))
            f2.Add(f2.Get(f2.Size-1))
            f3.Add(f3.Get(f3.Size-1))
            f4.Add(f4.Get(f4.Size-1))
            f5.Add(f5.Get(f5.Size-1))
            f6.Add(f6.Get(f6.Size-1))        
        End If
     
    Next
    Root.Visible=True
    btn1_Click
End Sub


Private Sub btn6_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn6.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn6.Text, xui.Color_Yellow)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f6)
    SortedData.Sort(True)
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
     
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f6.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Private Sub btn5_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn5.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn5.Text, xui.Color_Magenta)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f5)
    SortedData.Sort(True)
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
     
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f5.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Private Sub btn4_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn4.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn4.Text, xui.Color_Cyan)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f4)
    SortedData.Sort(True)
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
     
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f4.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Private Sub btn3_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn3.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn3.Text, xui.Color_Blue)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f3)
    SortedData.Sort(True)
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
     
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f3.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Private Sub btn2_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn2.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn2.Text, xui.Color_Green)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f2)
    SortedData.Sort(True)
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
     
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f2.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Private Sub btn1_Click
    ' Initialize the single line data
    ' Remember to set the chart type in designer or use the type attribute
    SingleLine1.ClearData
 
    SingleLine1.Title = txt_name.Text
    SingleLine1.XAxisName = "Time"
    SingleLine1.YAxisName = btn1.Text
    SingleLine1.IncludeLegend = "BOTTOM"
    SingleLine1.XScaleTextOrientation = "VERTICAL"
    SingleLine1.AddLine(btn1.Text, xui.Color_Red)
    SingleLine1.AutomaticScale = False
 
    SortedData.Clear
    SortedData.AddAll(f1)
    SortedData.Sort(True)
 
    MinMax(SortedData.Get(0), SortedData.Get(SortedData.Size-1))
'    SingleLine1.YScaleMinValue=SortedData.Get(0)
'    SingleLine1.YScaleMaxValue=SortedData.Get(SortedData.Size-1)
 
    For i=0 To ChartTime.Size-1
        SingleLine1.AddLinePointData(ChartTime.Get(i), f1.Get(i), i Mod Xdivisions = 0)
    Next
    SingleLine1.DrawChart
End Sub

Sub ConverttoMEZ (s As String) As String
    Dim t As Long
    t=DateTime.TimeParse(s)
    t=t+(DateTime.TimeZoneOffset*DateTime.TicksPerHour)
    Return DateTime.Time(t)
End Sub

'    Data from JSON Tree Example
#Region
'    Dim elevation As String = channel.Get("elevation")
'    Dim last_entry_id As Int = channel.Get("last_entry_id")
'    Dim latitude As String = channel.Get("latitude")
'    Dim description As String = channel.Get("description")
'    Dim created_at As String = channel.Get("created_at")
'    Dim field1 As String = channel.Get("field1")
'    Dim updated_at As String = channel.Get("updated_at")
'    Dim name As String = channel.Get("name")
'    Dim field6 As String = channel.Get("field6")
'    Dim id As Int = channel.Get("id")
'    Dim field3 As String = channel.Get("field3")
'    Dim field2 As String = channel.Get("field2")
'    Dim field5 As String = channel.Get("field5")
'    Dim longitude As String = channel.Get("longitude")
'    Dim field4 As String = channel.Get("field4")
'    Dim feeds As List = MyRoot.Get("feeds")
'    For Each colfeeds As Map In feeds
'        Dim field1 As String = colfeeds.Get("field1")
'        Dim created_at As String = colfeeds.Get("created_at")
'        Dim field6 As String = colfeeds.Get("field6")
'        Dim field3 As String = colfeeds.Get("field3")
'        Dim entry_id As Int = colfeeds.Get("entry_id")
'        Dim field2 As String = colfeeds.Get("field2")
'        Dim field5 As String = colfeeds.Get("field5")
'        Dim field4 As String = colfeeds.Get("field4")
'    Next
#End Region

Private Sub btn_month_Click
    nResults=2880
    Xdivisions=nResults/10
    'LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=48"$
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
    GetData(LinkURL)
End Sub

Private Sub btn_week_Click
    nResults=672
    Xdivisions=nResults/10
    'LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=16"$
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
    GetData(LinkURL)
End Sub

Private Sub btn_day_Click
    nResults=96
    Xdivisions=nResults/10
    'LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?Days=1"$
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
    GetData(LinkURL)
End Sub

Private Sub btn_max_Click
    nResults=8000
    Xdivisions=nResults/10
    'LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?Days=1"$
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
    GetData(LinkURL)
End Sub

Private Sub cb1_ValueChanged (Value As Object)
    ChannelNumber=Value
    nResults=96
    Xdivisions=nResults/10
    'LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?Days=1"$
    LinkURL=$"https://api.thingspeak.com/channels/${ChannelNumber}/feeds.json?results=${nResults}"$
    GetData(LinkURL)
End Sub

private Sub MinMax(ymin As Int, ymax As Int)
    Dim difference As Int=ymax-ymin
    Dim ydivision As Int=difference/10
    Dim miny, maxy As Int
    miny=ymin-ydivision
    maxy=ymax+ydivision
    'Return Array As Int(miny, maxy)
    SingleLine1.YScaleMinValue=miny
    SingleLine1.YScaleMaxValue=maxy
End Sub

1644758342059.png

Click in the graph to view the data (Not here of course, this is a screenshot!).

And last but not least, the project as a zip file.
 

Attachments

  • Thingspeak.zip
    49.7 KB · Views: 119
Last edited:

Mark Read

Well-Known Member
Licensed User
Longtime User
As a result of a conversation with Klaus, the following changes have been made:

1. xChart.bas is updated to the lastest version which fixes a bug in the scaling of the chart.

2. The calculation of the min and max values for the y-axis is better - thanks to Klaus.

Updated version:
private Sub MinMax(ymin As Double, ymax As Double)
'    Dim difference As Double=ymax-ymin
'    Dim ydivision As Double=difference/10
'    Dim miny, maxy As Int
'    miny=Floor(ymin-ydivision)
'    maxy=Floor(ymax+ydivision)
'   
'    SingleLine1.YScaleMinValue=miny
'    SingleLine1.YScaleMaxValue=maxy
'   
'    Log("Miny: " & miny)
'    Log("Maxy: " & maxy)

    Dim ValMin, ValMax As Int
    ValMin = Floor(ymin)
    ValMax = Ceil(ymax)
    Dim difference As Int = ValMax - ValMin
    Dim ydivision As Int = difference / 10
    Dim miny, maxy As Int
    miny = ValMin - ydivision
    maxy = ValMax + ydivision
    'Return Array As Int(miny, maxy)
    SingleLine1.YScaleMinValue=miny
    SingleLine1.YScaleMaxValue=maxy
End Sub

The new version is in the first post.
 
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