convert listboxvalue to double???? VB.NEt

G

gtjr92

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May 12, 2005
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14
I am trying to get an average of some row totals. I know how to do that, but my average depends on what value is selected in my listbox(lbxwkid)
Conversion from string "" to type 'Double' is not valid. for this line
ElseIf lbxWkid.SelectedValue().ToString > 0 Then

HEre is my code the tithecountsum is also a double.
Code: 
ElseIf lbxWkid.SelectedValue().ToString > 0 Then
ElseIf lbxWkid.SelectedValue().ToString > 0 Then         
 Dim lbxValue As Double = Convert.ToDouble(lbxWkid.SelectedValue)
            TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)
 
Conversion from string "" to type 'Double'
Click to expand...

From reading this it is trying to convert an empty string, which will not work. Try checking that the value selected in the listbox is actually populate before trying to convert it.
 
tried that...

Tried that I got object reference not set to an instance of an object
Code: 
 ElseIf lbxWkid.SelectedItem.Selected = True Then
                   Dim lbxValue As Double = Convert.ToDouble(lbxWkid.SelectedItem.Value)
            TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)
        ElseIf lbxWkid.SelectedItem.Selected = False Then
        End If
 
re:

PlausiblyDamp said:
Which line did the error occur on though? Also is an item selected?
Click to expand...

It throws the error for this line
ElseIf lbxWkid.SelectedItem.Selected = True Then

Here is the full error

System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
Source="App_Web_xi7tdrfw"
StackTrace:
at YearlyOff.ComputeSum(Object sender, GridViewRowEventArgs e) in H:\ASPNET20\WebSites\GBCTithe\YearlyOff.aspx.vb:line 57

at System.Web.UI.WebControls.GridView.OnRowDataBound(GridViewRowEventArgs e)

at System.Web.UI.WebControls.GridView.CreateRow(Int32 rowIndex, Int32 dataSourceIndex, DataControlRowType rowType, DataControlRowState rowState, Boolean dataBind, Object dataItem, DataControlField[] fields, TableRowCollection rows, PagedDataSource pagedDataSource)

at System.Web.UI.WebControls.GridView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding)

at System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data)

at System.Web.UI.WebControls.GridView.PerformDataBinding(IEnumerable data)

at System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data)

at System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback)

at System.Web.UI.WebControls.DataBoundControl.PerformSelect()

at System.Web.UI.WebControls.BaseDataBoundControl.DataBind()

at System.Web.UI.WebControls.GridView.DataBind()

at System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound()

at System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls()

at System.Web.UI.Control.EnsureChildControls()

at System.Web.UI.Control.PreRenderRecursiveInternal()

at System.Web.UI.Control.PreRenderRecursiveInternal()

at System.Web.UI.Control.PreRenderRecursiveInternal()

at System.Web.UI.Control.PreRenderRecursiveInternal()

at System.Web.UI.Control.PreRenderRecursiveInternal()

at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
 
Change:

ElseIf lbxWkid.SelectedItem.Selected = True Then

To:

ElseIf Not lbxWkid.SelectedItem Is Nothing Then

Or more commonly seen you could:

If Not lblWkik.SelectedIndex = -1 Then
'Code for what to do when there is a selected item (-1 means no selection, so
'thus if it is not -1 then an item has been selected
End If

Both will work, it's just a coding style/preference thing. Also you should always have your most common condition in the 'If' clause and non-common conditions in the else clause...so since your selection box will probably have a selection more often than it does not, the part that goes in the 'If' clause would be the checking for whether there is a selected item or not, and the else clause would be the logic for what to do when there isn't something selected. There's no rules on that, just something that most people will say is good practice/coding.

What you originally had is telling .NET to test for whether the selected item in the list is selected (which a selected item would be), you want to see if there is a selected item.
 
no go...

Ok here is everthing I have tried and the results...
Code: 
ElseIf Not lbxWkid.SelectedItem Is Nothing Then
Page loads, when I click an item the page postback but nothing shows up in the lblavg text box No errors are thrown.

Code: 
If Not lblWkik.SelectedIndex = -1 Then
Page loads, when I click an item the page postback but nothing shows up in the lblavg text box No errors are thrown.


Code: 
ElseIf lbxWkid.SelectedValue <> "" Then
Page loads, when I click an item the page postback but nothing shows up in the lblavg text box No errors are thrown.

If I do this

Code: 
    ElseIf lbxWkid.SelectedIndex > -1 Then
    ElseIf IsNumeric(lbxWkid.SelectedValue) Then

Page loads, when I click an item the page postbacks but nothing shows up in the lblavg text box
No errors are thrown

When I try this

Code: 
ElseIf lbxWkid.SelectedItem.Text > 0 Then
Object reference not set to an instance of an object.

If I try this

Code: 
ElseIf cdbl(lbxWkid.SelectedValue) > 0 Then
I get
Input string was not in a correct format.


Here is my "then" code which I know works because if I take out the if statements and change titheavg = tithecountsum / 20 my lblavg shows the value of titheavg.

Code: 
Dim lbxValue As Double = CDbl(lbxWkid.SelectedItem.Value)
            TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)

This is for asp.net 2.0 I don't think that matters though.
 
Ok I figured out some more If I take the if statement and make it a seperate sub and execute that sub on listbox selected change like this (I am using asp.net 2.0)

Code: 
Partial Class YearlyOff
    Inherits System.Web.UI.Page
    Dim TitheCountSum As Double = 0
    Dim EducationCountSum As Double = 0
    Dim MissionCountSum As Double = 0
    Dim SpecialCountSum As Double = 0
    Dim GiftValueCountSum As Double = 0
    Dim OfferingTotal As Double = 0
    Dim DepositTotal As Double = 0
    Dim Weekid As Double = 0
    Dim Datewk As Date
    Dim TitheAvg As Double = 0

Sub ComputeAvg(ByVal Sender As Object, ByVal e As EventArgs)
        If Not lbxWkid.SelectedIndex = -1 Then
            Then
            Dim lbxValue As Double = CDbl(lbxWkid.SelectedItem.Text)
                       TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = lbxWkid.SelectedValue & String.Format("{0:c}", TitheAvg)
        End If
    End Sub
My lblavg.text gets $0.00 this is because tithecount sum is a default value of zero before it evals the sumoftithe field. My eval tithcountsum evals that field in another sub.
I even tried to create a new if statement within the same sub and nothing happens like my previous post.

Here is all of my code for the sub i originally reffered too This sub is run on rowdatabound
Code: 
 Public Sub ComputeSum(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
       

        If e.Row.RowType = DataControlRowType.DataRow Then
            'ListItemType.item = ListItemType.AlternatingItem Then
            'Snip out the Total of Each Row & Column
            Datewk = Convert.ToDateTime(DataBinder.Eval(e.Row.DataItem, "Date"))
            Weekid = Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "WEEK"))
            TitheCountSum += Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "SumofTithe"))
            EducationCountSum += Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "SumofEducation"))
            MissionCountSum += Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "SumofMissions"))
            SpecialCountSum += Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "SumOfSpecial"))
            'GiftValueCountSum += Convert.ToDouble(DataBinder.Eval(e.Row.DataItem, "Gift_Value"))
            OfferingTotal = TitheCountSum + MissionCountSum + SpecialCountSum
            DepositTotal = TitheCountSum + MissionCountSum + SpecialCountSum + EducationCountSum
            'lbxValue += Convert.ToDouble(lbxWkid.SelectedValue)
            'Label2.Text = "Tot Offering* " & String.Format("{0:C}", OfferingTotal)
            LblOfferingTot.Text = "Total Offering* " & String.Format("{0:C}", OfferingTotal)
            LblTithe.Text = "Total Tithe: " & String.Format("{0:C}", TitheCountSum)
            LblEducation.Text = "Total Education: " & String.Format("{0:C}", EducationCountSum)
            LblMissions.Text = "Total Missions: " & String.Format("{0:C}", MissionCountSum)
            LblSpecial.Text = "Total Special: " & String.Format("{0:C}", SpecialCountSum)
            LblDepositTot.Text = "Total Deposit* " & String.Format("{0:C}", DepositTotal)
            Lblstar.Text = "Total Offering =Tithe Total + Mission Total + Special Total"
            LblDeposit.Text = "Total Deposit=Tithe Total + Mission Total + Special Total + Education Total"
            

        ElseIf e.Row.RowType = DataControlCellType.Footer Then
            e.Row.RowType = DataControlCellType.Footer
            e.Row.Cells.Item(3).Text = "Total Ti: " & String.Format("{0:C}", TitheCountSum)
            e.Row.Cells.Item(4).Text = "Total Ed: " & String.Format("{0:C}", EducationCountSum)
            e.Row.Cells.Item(5).Text = "Total Mis: " & String.Format("{0:C}", MissionCountSum)
            e.Row.Cells.Item(6).Text = "Total SP: " & String.Format("{0:C}", SpecialCountSum)

[COLOR=DarkRed]'I had the statment I am having trouble with inside this if statment as an ElseIF Like this[/COLOR]
ElseIf Not lbxWkid.SelectedIndex = -1 Then
             Then
            Dim lbxValue As Double = CDbl(lbxWkid.SelectedItem.Text)
           TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)
            
        End If
[COLOR=DarkRed]'and I Also tried as a seperated If statement in the same sub. Neither of these gives me a value in my lblavg.text[/COLOR] 
        If Not lbxWkid.SelectedIndex = -1 Then
            'ElseIf Not lbxWkid.SelectedItem Is Nothing Then
            Dim lbxValue As Double = CDbl(lbxWkid.SelectedItem.Text)
            TitheAvg = TitheCountSum / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)
        End If
    End Sub
 
Finally

FINALLY I got it for whatever reason that if statement would not execute in the computesum sub so I created a hidden field in the compute sum sub, I drew the tithecountsumvalue from another label into the hidden field, rather than use the tithecountsum. I then created a new sub and ran that on the gridview -onprerender Worked like a charm! If there is an easier way that someone knows how to do this feel free to comment but this worked after the tons of things i tried!
Code: 
 Sub ComputeAvg(ByVal Sender As Object, ByVal e As EventArgs)
        If Not lbxWkid.SelectedIndex = -1 Then
              Dim lbxValue As Double = CDbl(lbxWkid.SelectedItem.Text)
            Dim TitheVal As String = hidTithesum.Value
            TitheAvg = TitheVal / lbxValue
            lblAvg.Text = String.Format("{0:c}", TitheAvg)
 
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