How to implement a class extension

In this topic

• About implementing a class extension
• Develop a class extension
• Create a Java class
• Annotate a Java class
• Add implementation code
• Export as a JAR file
• Deploy a class extension
• Apply a class extension

About implementing a class extension

Develop a class extension

Create a Java class

• IObjectClassValidation—Implements custom attribute validation
• IObjectClassEvents—Implements custom object event behavior
• IRelatedObjectClassEvents and IRelatedObjectClassEvents2—Implement custom relationship behavior

• Customize attribute validation
• Customize relationship behavior
• Customize object event behavior

Annotate a Java class

//Create a Java class.
//Annotate the Java class.
@ArcGISExtension(categories = {
    ArcGISCategories.GeoObjectClassExtensions
}

)public class FirstClassExtension implements IClassExtension, IObjectClassExtension,
    IFeatureClassExtension{}

Add implementation code

• init—This method is invoked by the ArcGIS runtime when the class extension is initialized. Class extensions are initialized when they are applied to an existing class or when their applied class is accessed by an ArcGIS client. When invoking the init() method, the ArcGIS framework provides the following parameter references that can be crucial for other methods to operate correctly: 
• IClassHelper—The class helper parameter provides the object reference of the object or feature class to which the class extension is applied. Many extensions require an object reference. For example, with the init() method, the class helper parameter provides reference to the feature table to which the class extension is applied. The reference parameter allows you to access the properties of the feature class and its attributes and values.
• IPropertySet—The property set parameter contains the properties of the class extension with regard to the applied object or feature class. These properties can include strings, images, and other objects that are relevant to implementation of the class extension. The properties are persisted to the geodatabase as metadata on a class-by-class basis for each table or feature class to which the class extension is applied. This allows each class extension table or feature class to be configured individually. 
  Property values can be modified at any time by casting the object class reference to the IClassSchemaEdit2 interface and calling the alterClassExtensionProperties method with a new set of properties as a parameter. As with other methods in the IClassSchemaEdit interface, you need to obtain an exclusive schema lock for the class prior to modifying its extension properties. When an object or feature class with an associated class extension is created, it has no extension properties and the value passed to the IClassExtension.init() method's parameter is null. If properties are required for the extension to operate correctly, the init() method can check whether the incoming property set is null, and if so, apply a default set of properties and persist the property values by invoking the IClassSchemaEdit2.alterClassExtensionProperties() method.
• shutdown—This method is called when its associated object or feature class is disposed of or when the extensions are removed from the class.

• The string values of the CREATED_FIELD_PROPERTY and MODIFIED_FIELD_PROPERTY class variables are the properties of the class extension. You can determine the value of the properties by using IPropertySet.getProperty(). You can also alter the property values using IPropertySet.setProperty() and persist the properties to their object class using IClassSchemaEdit2.alterClassExtensionProperties().
• The object reference to which the class extension is applied is derived from the class helper parameter using the IClassHelper.esri_getClass() method.

//Declare class variables.
// The property set keys are used to get and set the extension properties.
public final static String CREATED_FIELD_PROPERTY = "CREATION_FIELDNAME";
public final static String MODIFIED_FIELD_PROPERTY = "MODIFICATION_FIELDNAME";

// Use the default field names as timestamp fields if none are defined when the
//class extension is applied.
private final static String DEFAULT_CREATED_FIELD = "CREATED";
private final static String DEFAULT_MODIFIED_FIELD = "MODIFIED";

/**
 * The indexes of the timestamp fields in the extension class. A value of -1 indicates
 * that the field is not used or could not be found during initialization.
 */
private int createdFieldIndex =  - 1;
private int modifiedFieldIndex =  - 1;

/************************************************************************************************
 * IClassExtension members
 ************************************************************************************************/

// Initialize the extension, passing in a reference to its class helper and its extension properties.

public void init(IClassHelper classHelper, IPropertySet extensionProperties)throws
    IOException, AutomationException{
    // Get a reference to the extension's object class.
    IClass baseClass = classHelper.esri_getClass();
    // Make sure a valid property set is provided.
    if (extensionProperties != null && extensionProperties.getCount() != 0){
        // Get the field names from the property set.
        Object createdFieldProperty = extensionProperties.getProperty
            (CREATED_FIELD_PROPERTY);
        Object modifiedFieldProperty = extensionProperties.getProperty
            (MODIFIED_FIELD_PROPERTY);

        // Get the created field index.
        if (createdFieldProperty != null){
            createdFieldIndex = baseClass.findField(createdFieldProperty.toString());
        }
        // Get the modified field index.
        if (modifiedFieldProperty != null){
            modifiedFieldIndex = baseClass.findField(modifiedFieldProperty.toString()
                );
        }
    }
    else{
        // If the extension properties are null or empty, assume the class has
        // been created without extension properties. Apply the default property values.
        ISchemaLock schemaLock = null;
        try{
            // Attempt to acquire an exclusive schema lock. If this fails, an
            // AutomationException will be raised.
            schemaLock = new ISchemaLockProxy(classHelper.esri_getClass());
            schemaLock.changeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock);
            // Create a default set of extension properties.
            IPropertySet propertySet = new PropertySet();
            propertySet.setProperty(CREATED_FIELD_PROPERTY, DEFAULT_CREATED_FIELD);
            propertySet.setProperty(MODIFIED_FIELD_PROPERTY, DEFAULT_MODIFIED_FIELD);
            // Use the IClassSchemaEdit2 interface to persist a new set of extension properties.
            IClassSchemaEdit2 classSchemaEdit2 = new IClassSchemaEdit2Proxy
                (classHelper.esri_getClass());
            classSchemaEdit2.alterClassExtensionProperties(propertySet);
        }
        catch (AutomationException autoExc){
            // An exclusive schema lock could not be acquired. Allow the extension to
            // finish initializing; no custom behavior will occur.
        }
        finally{
            try{
                // Ensure that the schema lock is shared.
                if (schemaLock != null)
                    schemaLock.changeSchemaLock(esriSchemaLock.esriSharedSchemaLock);
            }
            catch (Exception exc){
                // Ignore any errors at this point.
            }
        }
    }
}

/**
 * Called when the extension's class is being disposed of from memory.
 */
public void shutdown()throws IOException, AutomationException{
    // Do nothing.
}

Export as a JAR file

Deploy a class extension

Apply a class extension

• To apply an extension when creating new object or feature classes, pass a fully qualified class name of the annotated Java class of the class extension to the IFeatureWorkspace.createTable() or IFeatureWorkspace.createFeatureClass() method.
• To apply an extension to an existing class, invoke the IClassSchemaEdit.alterClassExtensionCLSID() method programmatically and pass the fully qualified class name of the annotated Java class of the class extension. This method can also be used to remove a class extension by providing null values as parameters.

See Also: