Codebehind for conditional visibility

Nostromo77 · September 11th, 2008, 12:16 PM

I suspect that the answer to this is going to be so simple that I will kick myself when I see it, but I can seem to figure it out...

I have a shopping cart engine that has fields for both Price and SalePrice. Right now the Price displays just fine, and the SalePrice displays as well if I include it inside the cart's ItemTemplate tag:

Code:

<dotnetCART:DisplayCatalog>
<ItemDetailsTemplate>
<asp:label id="myPrice" Text="Price:" runat="server" />
<%#Container.Price%>
<br />
<%#Container.SalePrice%>
</ItemDetailsTemplate>
</dotnetCART:DisplayCatalog>

I would like to arrange it so that the cart only shows the SalePrice when there is an actual value in the database's SalePrice field for that product's row. The aspx page code could look something like this:

Code:

<asp:panel id="pnlSalePrice" runat="server" visible="false">            
<asp:label id="mySalePrice" Text="Sale Price:" runat="server" />
<b>
<%#Container.SalePrice%>
</b>
</asp:panel>

What would the code behind for this look like to switch this panel "on" when the SalePrice does not equal null or $0.00?

Thanks for any help!

planoie · September 11th, 2008, 12:33 PM

I think you should be able to databind the visible property like this:

<asp:panel id="pnlSalePrice" runat="server" visible='<%# CanShowPanel(Container.SalePrice) %>'>

Then, you could create a protected method in the code behind that does the test:

protected bool CanShowPanel(object salePrice){
return ((decimal)salePrice) != 0M;
}

You could put the test logic in the data binding code, but that gets things messier and you loose the compile type checking. It's not bulletproof, but at least it's better than clumsy code blobs in the markup.

-Peter
compiledthoughts.com

Nostromo77 · September 16th, 2008, 12:09 PM

Thank you, this worked perfectly! So that I understand how it is doing this, the code

Code:

protected bool CanShowPanel(object salePrice)
{
   return ((decimal)salePrice) != 0M;
}

...is asking CanShowPanel to return true if salePrice is not equal to 0M - M being the suffix to show currency. If I were creating a function like this to read a boolean field instead of a price, would it just be

Code:

return ((decimal)salePrice) != 0;

?

Edit:

I notice that while this function works fine for the product details view of my catalog, when I try to apply to a higher level og my displayCatalog component (a display of all products in a category), I get this error:

Conversion from string "" to type 'Decimal' is not valid.
100107
DisplayCatalog

...any idea why it might be doing this?

Thanks

planoie · September 16th, 2008, 01:53 PM

The M denotes that the literal value (0) is to be considered a decimal, versus an integer.

Testing for bool just becomes:

   return (bool)someValue;

It's breaking because whatever value it is that you are passing into the method is a string, not a decimal and thus can not be converted.

A generally better way of going about this would be to simply pass the whole object you are dealing with to the method and let the method check the appropriate property. That way you also move the property part of the non-compiled code into compiled code:

   <asp:panel id="pnlSalePrice" runat="server" visible='<%# CanShowPanel(Container) %>'>

Then you convert "Container" to whatever the whole object is, then query its property:

protected bool CanShowPanel(object myObject){
   return ((MyObjectType)myObject).SalePrice != 0M;
}

Then you risk less if you change the properties, because that code will break on compiled if you change SalePrice for example.

-Peter
compiledthoughts.com

Nostromo77 · September 21st, 2008, 08:00 PM

Thank you very much - I will try this.