Using textbox value as parameter in LINQ dat source/gridview : A value of type 'String' cannot be converted to type 'Double'

StackOverflow https://stackoverflow.com/questions/1999292

Question

it's a New Year but you're still left with a thick Mr Dean!!

Ok, the scenario - I have a textbox, a two radio buttons, a button and a gridview.

<code>

<body>

<form id="form1" name="form1" runat="server">



<asp:TextBox ID="tbxHowMany" runat="server" 
    style="z-index: 1; left: 245px; top: 105px; position: absolute; height: 20px; width: 345px;" 
    CssClass="completionList2"></asp:TextBox>   

    <asp:RadioButton ID="radGlass" runat="server" GroupName="WeightSearch" 
    style="z-index: 1; left: 655px; top: 150px; position: absolute" /> 

 <asp:RadioButton ID="radPaper" runat="server" GroupName="WeightSearch" 
    style="z-index: 1; left: 655px; top: 105px; position: absolute"/> 


<asp:Button ID="btnReturnWeight" runat="server" Text="Return Selected Weights" 
    onclick="btnReturnWeight_Click" 

    style="z-index: 1; left: 245px; top: 155px; position: absolute; right: 375px" 
    Height="25px" Width="350px" />

<asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
    AllowSorting="True" AutoGenerateColumns="False" 
    DataSourceID="LQTOPDS" CellPadding="4" Font-Size="X-Small" 
    ForeColor="#333333" GridLines="None" 
      style="z-index: 1; left: 0px; top: 530px; position: absolute; height: 295px; width: 1370px; text-align: center;" DataKeyNames="PriKey" 
        >
    <RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
    <Columns>


            <asp:BoundField DataField="UnitId" HeaderText="UnitId" 
            SortExpression="UnitId" />
            <asp:BoundField DataField="UnitDescription" HeaderText="UnitDescription" 
            SortExpression="UnitDescription" />
        <asp:BoundField DataField="SaleQty" HeaderText="SaleQty" 
            SortExpression="SaleQty" />
        <asp:BoundField DataField="LevelNo" HeaderText="LevelNo" 
            SortExpression="LevelNo" />
        <asp:BoundField DataField="MaterialId" HeaderText="MaterialId" 
            SortExpression="MaterialId" />
            <asp:BoundField DataField="PackagingTypeCode" HeaderText="PackagingTypeCode" 
                SortExpression="PackagingTypeCode" />
            <asp:BoundField DataField="UnitWeight" HeaderText="UnitWeight" 
                SortExpression="UnitWeight" />
            <asp:BoundField DataField="WeightUnitCode" HeaderText="WeightUnitCode" 
                SortExpression="WeightUnitCode" />
        <asp:BoundField DataField="WeightStatus" HeaderText="WeightStatus" 
            SortExpression="WeightStatus" />
        <asp:BoundField DataField="ProductPercentage" HeaderText="ProductPercentage" 
            SortExpression="ProductPercentage" />
        <asp:BoundField DataField="Comment" HeaderText="Comment" 
            SortExpression="Comment" />
        <asp:BoundField DataField="IDDesc" HeaderText="IDDesc" 
            SortExpression="IDDesc" />
            <asp:BoundField DataField="PriKey" HeaderText="PriKey" ReadOnly="True" 
                SortExpression="PriKey" />
    </Columns>
    <FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
    <SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
    <HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
    <EditRowStyle BackColor="#999999" />
    <AlternatingRowStyle BackColor="White" ForeColor="#284775" />
    </asp:GridView>


    <asp:LinqDataSource ID="LQTOPDS" runat="server" 
        ContextTypeName="CompleteWeightsDataContext" 
        TableName="tblOnlineReportingCOMPLETEWeights" 
        Where="ProductPercentage &lt;= Double(@ProductPercentage)" 
        onselecting="LQTOPDS_Selecting" OrderBy="ProductPercentage desc">
        <WhereParameters>
            <asp:ControlParameter ControlID="tbxHowMany" Name="ProductPercentage" 
                PropertyName="Text" Type="Double" />
        </WhereParameters>
    </asp:LinqDataSource>


</form>

</body>


</code>

What I am attempting to achieve is the following: A user types in a number into the textbox, the linq data source parameter is changed and uses this number. When the button is clicked, the gridview is displayed.

Now currently, I have the following in the code behind:

<code>

public partial class TOP___In_Development : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Session["MemberKey"] = "FM00012";

        }
    }

    protected void btnReturnWeight_Click(object sender, EventArgs e)
    {
        LQTOPDS.WhereParameters.Clear();
        ControlParameter cp = new ControlParameter();
        cp.Type = TypeCode.String;


            {
                if (radPaper.Checked)
                {

                    cp.ControlID = "tbxHowMany";
                    cp.PropertyName = "Text";
                    cp.Name = "ProductPercentage";
                    LQTOPDS.WhereParameters.Add(cp);
                    GridView1.DataSourceID = "LQTOPDS";
                    GridView1.DataBind();
                }

                else if (radGlass.Checked)
                {
                    Convert.ToDouble(tbxHowMany.Text);
                    cp.ControlID = "tbxHowMany";
                    cp.PropertyName = "Text";
                    cp.Name = "ProductPercentage";
                    LQTOPDS.WhereParameters.Add(cp);
                    GridView1.DataSourceID = "LQTOPDS";
                    GridView1.DataBind();
                }
            }
        }


    protected void LQTOPDS_Selecting(object sender, LinqDataSourceSelectEventArgs e)
    {
        foreach (KeyValuePair<string, object> kvp in e.WhereParameters)
        {
            if (kvp.Value == null)
            {
                e.Cancel = true;
                return;
            }
        }
    }

}

</code>

However, when I attempt to run this, the binding fails as "a value of type string' cannot be converted to type 'double'

How do I go about converting the textbox value within the btnReturnWeight_Click so that a double is used and, hopefully, the gridview is produced.

PS: I realise the if and else if conditions will produce the same results at present, I'll work on inserting additional parameters next!!

Any help would be gratefully received.

Was it helpful?

Solution

To convert a string to a double you can use;

   string value;

   value = Double.MinValue.ToString();
   try {
      Console.WriteLine(Double.Parse(value));
   }   
   catch (OverflowException) {
      Console.WriteLine("{0} is outside the range of the Double type.", value);
   }

   value = Double.MaxValue.ToString();
   try {
      Console.WriteLine(Double.Parse(value));
   }
   catch (OverflowException) {
      Console.WriteLine("{0} is outside the range of the Double type.", value);
   }


// The example displays the following output:
//    -1.79769313486232E+308 is outside the range of the Double type.
//    1.79769313486232E+308 is outside the range of the Double type.

If you want to check that a string is a valid double you can use try parse;

string value;
double number;

value = Double.MinValue.ToString();
if (Double.TryParse(value, out number))
   Console.WriteLine(number);
else
   Console.WriteLine("{0} is outside the range of a Double.", value);

value = Double.MaxValue.ToString();
if (Double.TryParse(value, out number))
   Console.WriteLine(number);
else
   Console.WriteLine("{0} is outside the range of a Double.", value);


// The example displays the following output:
//    -1.79769313486232E+308 is outside the range of the Double type.
//    1.79769313486232E+308 is outside the range of the Double type.

More details are accesible from all the major search engines, search them all at once here: http://www.liquidjelly.co.uk/supersearch/?q=double.tryparse()&lang=en-GB

HTH,
Mark

Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow
scroll top