Form Extensions

Form Extensions
The form extension works like any other extension; they are delta changes that are applied when the package is deployed. We can extend the functionality of a form by extending its controls and data sources. For example, in a form extension, we can:
•Add a new control.
•Enable or disable a control.
•Change the text or label property of a control.
•Change a control’s visibility.
•Change a form’s help text.
•Change a form’s caption.
•Add a new data source.
•Change properties at the data-source level.
•Add a form part.
In Microsoft Dynamics AX 2012, you could override form methods. In the current version, you use extensions to implement event handlers that are called from the base implementations of form methods.
Creating an Extension Class for Forms Code
To create an extension class for forms code, we can create a class which ends in _Extension. We only need to have the ExtensionOf decoration and ensure the name ends in _Extension. This capability made available with update 2 or platform 7.2.
So class declaration should read:
[ExtensionOf(formStr(FormName))]final class FormName_Extension{}
With extension classes we can add member variables, and these variables will be associated with the form. These variables can be referenced from any instance method. That way the state of the form can be maintained across different instance methods. Extension classes instantiate automatically; there is no access to private methods, but we can add state variables and access them along with forms public variables and methods.
The event handlers can be created as an instance methods. There are two types of event handler: a pre-event and post-event handler. Events are raised as preceding and succeeding operations around the base methods. We can write code to execute a before-base method or an after-base method. Microsoft Dynamics AX 2012 introduced XPP events, which are also available in this release and can be subscribed to in your extensions.
Events are exposed on the form designer on different elements, overridden methods and others.

•Copy event handler method: This option copies a method signature to the clipboard. You can paste it in any X++ code editor to define a method that subscribes to the selected event.
•Find event handlers: Searches and lists all methods subscribed to the selected event
Event Handler Methods Available with Form Datasource
An event handler method can be created on base datasource methods. All methods created will have FormDataSource _sender, FormDataSourceEventArgs _e as an argument.
Base methods can have preceding or succeeding events, but not all base methods have both events available. The following table shows events available with base datasource methods.

An argument of event handler can be used to get the FormDatasource, table record and formRun. Arguments can be manipulated and used in the following way:
Get formRun, Form control, datasource and selected record from form datasource
[FormDataSourceEventHandler(formDataSourceStr(MyForm, MyRandomTableDS), FormDataSourceEventType::Written)] public static void MyRandomTableDS_OnWritten(FormDataSource sender, FormDataSourceEventArgs e)
 {
 FormRun formRun = sender.formRun() as FormRun;
 // you can even call custom methods
 formRun.myCustomMethod();
// Get the selected datasource record
 TableName tableBuffer = sender.cursor();
// Get datasource variable
 FormDataSource DSVariable = sender.formRun().dataSource(“TableName”);
 }
Event Handler Methods Available with Form Object Methods
The following event handler methods are available with form object methods:

An event handler method will have xFormRun as an argument. The following example shows how to get datasource, form control from xFormRun argument.
Get form datasource from xFormRun
[FormEventHandler(formStr(SomeForm), FormEventType::Initialized)] public static void SomeForm_OnInitialized(xFormRun sender, FormEventArgs e)
 {
 FormDataSource MyRandomTable_ds = sender.dataSource(formDataSourceStr(SomeForm, MyRandomTableDS));
…
}
Access form control from xFormRun
[FormEventHandler(formStr(SomeForm), FormEventType::Initialized)] public static void SomeForm_OnInitialized(xFormRun sender, FormEventArgs e)
 {
 // set the control to invisible as an example
 sender.design().controlName(formControlStr(SomeForm, MyControl)).visible(false);
 }
 Event Handler Methods Available with Form Control Methods
The following event handler methods are available with form control methods:

Following example shows how we can get formRun from ‘FormControl’ argument, we can custom method with formRun. Datasource and current record can be obtained depending upon functionality we are working on.
Get FormRun from form control
[FormControlEventHandler(formControlStr(MyForm, MyButton), FormControlEventType::Clicked)] public static void MyButton_OnClicked(FormControl sender, FormControlEventArgs e)
 {
 FormRun formRun = sender.formRun() as FormRun;
 formRun.myCustomMethod();
 }
Get current record in form control event
[FormControlEventHandler(formControlStr(SomeForm, SomeButton), FormControlEventType::Clicked)] public static void SomeButton_OnClicked(FormControl sender, FormControlEventArgs e)
 {
 // as an example the datasource number is used for access; I perceive the formDataSourceStr as more robust
 SomeTable callerRec = sender.formRun().dataSource(1).cursor();
 }

Almost all customization can be done with extensions and event handlers in Dynamics 365 – there is no need to over-layer standard package. We have illustrated generic examples above, meanwhile more complex customizations can be done using event handlers.