Before I start, I
encourage you to go over Salesforce’s Visualforce Developer’s Guide which you
can find here. There is a section called “Dynamic
Visualforce Bindings” that already provides the syntax and more information about
the topic that I am discussing today.
If you don’t have time to
read the Developer’s Guide, or if you just want to quickly glance at what I have
to say today, then still please let me quickly talk about what exactly Dynamic
Visualforce Binding is. It is an
extremely powerful tool to build dynamic pages at run time.
We all know that Visualforce
is the “V” (view) part of the MVC paradigm that Salesforce uses. It indicates what the user interface of a
page is like. A traditional Visualforce page
denotes how the page should look like, what information is displayed, and in
what order. In other words, a
Visualforce page dictates what information the users see and how they see
it. The person that wrote the Visualforce page is in the driver's seat.
However, imagine this use
case. What if you want to display a list of accounts,
but you also want to give your users the flexibility to determine what information
about the account they want to see. You
may want to present a list of account related fields, and the users can select
what fields they want to see and in what order.
Having to program that logic can be a nightmare: the users may choose one field or ten fields, the users may choose Name first this time and then Name last next time. There are so many possibilities and combinations that, if not programmed
carefully, your code can become nothing but an endless list of if-then-else statements.
Enters Dynamic Visualforce Binding.
Let's just quickly see what a regular Visualforce page looks like. As an example I want to display the account name,
account number, annual revenue and ticker symbol of a list of accounts. To do that, all you need to do is a very
simple Visualforce page like this:
<apex:page standardController="account" recordSetVar="accounts">
<apex:pageBlock >
<apex:pageBlockTable value="{!accounts}" var="a">
<apex:column value="{!a.Name}" />
<apex:column value="{!a.AccountNumber}" />
<apex:column value="{!a.AnnualRevenue}" />
<apex:column value="{!a.TickerSymbol}" />
</apex:pageBlockTable>
</apex:pageBlock>
</apex:page>
Your page will look like this:
In order to use Dynamic Visualforce Binding, you need a little help from a controller. (I know it can be a turnoff, but no pain no gain!)
Let's take a look at the controller (again, I don't want to divulge into the syntax. Please refer to the Developer's Guide for the detailed syntax. I just want to show you how little code is required to unleash the power of Dynamic Visualforce Binding.)
public class AccountListDynamic
// accountFieldList is a property. It is a list of
// strings and each element in the list is the API
// name of the field that I want to display. This list
// is read-only.
public List<String> accountFieldList
{
get
{
if (accountFieldList == null)
{
accountFieldList.add('Name');
accountFieldList.add('AccountNumber');
accountFieldList.add('AnnualRevenue');
accountFieldList.add('TickerSymbol');
}
return accountFieldList;
}
private set;
}
}
I hope the class is quite self-explanatory. It is an extended controller (hence the ApexPages.standardSetController parameter in the constructor of the class). All that we are achieving here is to pass an array of account related field names (API names) and expose the list to the Visualforce page.
{
// constructor that simply adds the list of fields
// for the account.
// constructor that simply adds the list of fields
// for the account.
public AccountListDynamic(ApexPages.StandardSetController controller)
{
{
controller.addFields(accountFieldList);
}
// accountFieldList is a property. It is a list of
// strings and each element in the list is the API
// name of the field that I want to display. This list
// is read-only.
public List<String> accountFieldList
{
get
{
if (accountFieldList == null)
{
accountFieldList.add('Name');
accountFieldList.add('AccountNumber');
accountFieldList.add('AnnualRevenue');
accountFieldList.add('TickerSymbol');
}
return accountFieldList;
}
private set;
}
The Visualforce page now looks like this:
<apex:page standardController="account" recordSetVar="accounts" extensions="AccountListDynamic">
<apex:pageBlock >
<apex:pageBlockTable value="{!accounts}" var="a">
<apex:repeat value="{!accountFieldList}" var="f">
<apex:column value="{!a[f]}" />
</apex:repeat>
</apex:pageBlockTable>
</apex:pageBlock>
</apex:page>
<apex:pageBlock >
<apex:pageBlockTable value="{!accounts}" var="a">
<apex:repeat value="{!accountFieldList}" var="f">
<apex:column value="{!a[f]}" />
</apex:repeat>
</apex:pageBlockTable>
</apex:pageBlock>
</apex:page>
The hardest part to understand is probably a[f] above. "a" is a loop variable for each account in the list. "f" is a loop variable for each field to display. Therefore to simply put, a[f] refers to the value of a specific field for a specific account.
So, sure now you have the controller that makes things look a little more complicated, but did you notice the controller now handles the list of fields. All the Visualforce page does is to simply take that list of fields and displays the relevant data; you do not have any field names hardcoded in the Visualforce page at all!
Now, going back to our use case. Let's say you want to show the user a list of all account related fields, so that the user has the ability to choose which fields they want to display and the order the fields are to display.
You will need a separate Visualforce page for that. Once you have built this new Visualforce page for that, then all you need to do is to capture the information in your controller. Then the Visualforce page shown above again can be used to display the information.
This is exactly what the example in the Developer's Guide, in section "Using Dynamic References for a User-Customizable Page", is about. It is an excellent read, and I urge you to take a look at this topic.
The most unfortunate thing is that this function is not stable. I have got the code to work in some environments but fail in others.
I followed the example as per the Developer's Guide and this is the error I received:
I have talked to Salesforce and it is now officially under the "Known Issues" list. If you are interested, you can take a look at this page for more details. If you can replicate this error too, I strongly encourage you to click the "This Issue Affects Me" button. Note that the example there is quite different, but it still exposes the defect related to Dynamic Visualforce Binding.
