Form event handlers in D365FO

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));
    ...
}

Get FormRun 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 (I think IntelliSense won't work though)
    formRun.myCustomMethod();
}

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();
}

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);
}

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();
}

Convert Common and use DataEventArgs

[DataEventHandler(tableStr(AnyTable), DataEventType::ValidatedWrite)]
public static void InventLocation_onValidatedWrite(Common sender, DataEventArgs e)
{
    // convert Common to AnyTable
    AnyTable anyTable = sender;
    // the DataEventArgs actually are ValidateEventArgs and can be converted
    ValidateEventArgs validateEventArgs = e;
    // the ValidateEventArgs carry the validation result (so far)
    boolean ret = validateEventArgs.parmValidateResult();
    // the table has some additional validation logic and gives back the result
    ret = anyTable.doSomeAdditionalCustomValidation(ret);
    // provide the args with the validation result
    validateEventArgs.parmValidateResult(ret);
}

Use the onValidatedFieldValue event properly

[DataEventHandler(tableStr(SomeTable), DataEventType::ValidatedFieldValue)]
public static void SomeTable_onValidatedFieldValue(Common sender, DataEventArgs e)
{
    SomeTable someTable = sender;
    // the clue is to know that the DataEventArgs actually are ValidateFieldValueEventArgs and that you can get the field name from them
    ValidateFieldValueEventArgs validateEventArgs = e;
    boolean ret = validateEventArgs.parmValidateResult();
    FieldName fieldName = validateEventArgs.parmFieldName();
    switch (fieldName)
    {
        case fieldStr(SomeTable, SomeCustomField):
            ... do some magic
            break;
    }
    validateEventArgs.parmValidateResult(ret);
}

Use the MappedEntityToDataSource event

[DataEventHandler(tableStr(MyTableEntity), DataEventType::MappedEntityToDataSource)]
public static void MyTableEntity_onMappedEntityToDataSource(Common _sender, DataEventArgs _eventArgs)
{
    DataEntityContextEventArgs eventArgs = _eventArgs;
    MyTableEntity entity = _sender;
    if (eventArgs.parmEntityDataSourceContext().name() == dataEntityDataSourceStr(MyTableEntity, MyTable))
    {
        MyTable myTable = eventArgs.parmEntityDataSourceContext().getBuffer();
        ... do some magic with it
    }
}