Visualforce Developer Guide
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Dynamic References to Action Methods Using $Action
The $Action global variable allows you to
dynamically reference valid actions on an object type, or on a specific record. The most
likely way to make use of this is to create a URL to perform that action.
For example, you can use the expression {!URLFOR($Action[objectName].New)} in an <apex:outputLink>, with a controller method getObjectName() that provides the name of the sObject.
Here’s an example that does exactly that. The controller extension queries the
system to learn the names of all the custom objects accessible to the user, and presents
a list of them, along with links to create a new record. First, create a controller
extension named DynamicActionsHandler:
public with sharing class DynamicActionsHandler {
public List<CustomObjectDetails> customObjectDetails { get; private set; }
public DynamicActionsHandler(ApexPages.StandardController cont) {
this.loadCustomObjects();
}
public void loadCustomObjects() {
List<CustomObjectDetails> cObjects = new List<CustomObjectDetails>();
// Schema.getGlobalDescribe() returns lightweight tokens with minimal metadata
Map<String, Schema.SObjectType> gd = Schema.getGlobalDescribe();
for(String obj : gd.keySet()) {
if(obj.endsWith('__c')) {
// Get the full metadata details only for custom items
Schema.DescribeSObjectResult objD = gd.get(obj).getDescribe();
if( ! objD.isCustomSetting()) {
// Save details for custom objects, not custom settings
CustomObjectDetails objDetails = new CustomObjectDetails(
obj, objD.getLabel(), objD.isCreateable());
cObjects.add(objDetails);
}
}
}
cObjects.sort();
this.customObjectDetails = cObjects;
}
public class CustomObjectDetails implements Comparable {
public String nameStr { get; set; }
public String labelStr { get; set; }
public Boolean creatable { get; set; }
public CustomObjectDetails(String aName, String aLabel, Boolean isCreatable) {
this.nameStr = aName;
this.labelStr = aLabel;
this.creatable = isCreatable;
}
public Integer compareTo(Object objToCompare) {
CustomObjectDetails cod = (CustomObjectDetails)objToCompare;
return(this.nameStr.compareTo(cod.nameStr));
}
}
}- The loadCustomObjects method uses Apex schema methods to get metadata information about available custom objects. The Schema.getGlobalDescribe method is a lightweight operation to get a small set of metadata about available objects and custom settings. The method scans the collection looking for items with names that end in “__c”, which indicates they are custom objects or settings. These items are more deeply inspected using getDescribe, and selected metadata is saved for the custom objects.
- Using if(obj.endsWith('__c')) to test whether an item is a custom object or not may feel like a “hack”, but the alternative is to call obj.getDescribe().isCustom(), which is expensive, and there is a governor limit on the number of calls to getDescribe. Scanning for the “__c” string as a first pass on a potentially long list of objects is more efficient.
- This metadata is saved in an inner class, CustomObjectDetails, which functions as a simple structured container for the fields to be saved.
- CustomObjectDetails implements the Comparable interface, which makes it possible to sort a list of custom objects details by an attribute of each object, in this case, the custom object’s name.
Now create a Visualforce page with
the following
markup:
<apex:page standardController="Account"
extensions="DynamicActionsHandler">
<br/>
<apex:dataTable value="{!customObjectDetails}" var="coDetails">
<apex:column >
<apex:facet name="header">Custom Object</apex:facet>
<apex:outputText value="{!coDetails.labelStr}"/>
</apex:column>
<apex:column >
<apex:facet name="header">Actions</apex:facet>
<apex:outputLink value="{!URLFOR($Action[coDetails.nameStr].New)}"
rendered="{!coDetails.creatable}">[Create]</apex:outputLink><br/>
<apex:outputLink value="{!URLFOR($Action[coDetails.nameStr].List,
$ObjectType[coDetails.nameStr].keyPrefix)}">[List]</apex:outputLink>
</apex:column>
</apex:dataTable>
</apex:page>