The source code for this lesson is provided in the 'HIIFormCallbackDebug' driver which is based on our standard varstore HII driver.
In all our earlier experiments with the EFI_HII_CONFIG_ACCESS_PROTOCOL functions the driver Callback() function was never called.
This has happend because none of the driver form elements had EFI_IFR_FLAG_CALLBACK flag set.
The EFI_IFR_FLAG_CALLBACK is one of the flags for the EFI_IFR_QUESTION_HEADER.flags field https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Uefi/UefiInternalFormRepresentation.h:
//
// Flag values of EFI_IFR_QUESTION_HEADER
//
#define EFI_IFR_FLAG_READ_ONLY 0x01
#define EFI_IFR_FLAG_CALLBACK 0x04
#define EFI_IFR_FLAG_RESET_REQUIRED 0x10
#define EFI_IFR_FLAG_REST_STYLE 0x20
#define EFI_IFR_FLAG_RECONNECT_REQUIRED 0x40
#define EFI_IFR_FLAG_OPTIONS_ONLY 0x80The EFI_IFR_QUESTION_HEADER in turn is a structure present in the IFR code of all our data elements:
EFI_IFR_CHECKBOX - checkbox
EFI_IFR_NUMERIC - numeric
EFI_IFR_STRING - string
EFI_IFR_DATE - date
EFI_IFR_TIME - time
EFI_IFR_ONE_OF - oneof
EFI_IFR_ORDERED_LIST - orderedlist
So let's add EFI_IFR_FLAG_CALLBACK to one of our form elements. For example let's add it to the numeric element. In the VFR code the necessary flag is indicated by the INTERACTIVE keyword:
numeric
name = NumericQuestion,
varid = FormData.NumericValue,
prompt = STRING_TOKEN(NUMERIC_PROMPT),
help = STRING_TOKEN(NUMERIC_HELP),
- flags = NUMERIC_SIZE_2 | DISPLAY_UINT_HEX,
+ flags = NUMERIC_SIZE_2 | DISPLAY_UINT_HEX | INTERACTIVE,
minimum = 0,
maximum = 10,
step = 1,
default = 7, defaultstore = StandardDefault,
default = 8, defaultstore = ManufactureDefault,
endnumeric;
Here is a description for the EFI_HII_CONFIG_ACCESS_PROTOCOL.CallBack() function from the UEFI specification:
EFI_HII_CONFIG_ACCESS_PROTOCOL.CallBack()
Summary:
This function is called to provide results data to the driver.
Prototype:
typedef
EFI_STATUS
(EFIAPI *EFI_HII_ACCESS_FORM_CALLBACK) (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN EFI_BROWSER_ACTION Action,
IN EFI_QUESTION_ID QuestionId,
IN UINT8 Type
IN OUT EFI_IFR_TYPE_VALUE *Value,
OUT EFI_BROWSER_ACTION_REQUEST *ActionRequest,
);
Parameters:
This Points to the EFI_HII_CONFIG_ACCESS_PROTOCOL
Action Specifies the type of action taken by the browser
QuestionId A unique value which is sent to the original exporting driver so that it can identify the
type of data to expect. The format of the data tends to vary based on the opcode that generated the callback
Type The type of value for the question
Value A pointer to the data being sent to the original exporting driver. The type is specified by Type
ActionRequest On return, points to the action requested by the callback function
Description
This function is called by the forms browser in response to a user action on a question which has the
EFI_IFR_FLAG_CALLBACK bit set in the EFI_IFR_QUESTION_HEADER. The user action is specified by
Action. Depending on the action, the browser may also pass the question value using Type and Value.
Upon return, the callback function may specify the desired browser action.
To better understand when and how this function is called let's add a debug statement that would print incoming arguments like we did with RouteConfig() and ExtractConfig(). But first let's try to understand what all these arguments mean.
This argument describes an operation that is currently performed by the browser. UEFI specification defines a list of possible browser operations with the EFI_BROWSER_ACTION type. The EFI_BROWSER_ACTION is UINTN with possible values described in the https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/HiiConfigAccess.h:
typedef UINTN EFI_BROWSER_ACTION;
#define EFI_BROWSER_ACTION_CHANGING 0 // Called after the user have changed the element value, but before the browser updated display
#define EFI_BROWSER_ACTION_CHANGED 1 // Called after the user have changed the element value, after the browser updated display
#define EFI_BROWSER_ACTION_RETRIEVE 2 // Called after the browser has read the value, but before displayed it
#define EFI_BROWSER_ACTION_FORM_OPEN 3 // Called on form open before retrieve
#define EFI_BROWSER_ACTION_FORM_CLOSE 4 // Called on form exit
#define EFI_BROWSER_ACTION_SUBMITTED 5 // Called after submit
#define EFI_BROWSER_ACTION_DEFAULT_STANDARD 0x1000 // Called on setting standard default (default value is equal 0x0000)
#define EFI_BROWSER_ACTION_DEFAULT_MANUFACTURING 0x1001 // Called on setting manufacture default (default value is equal 0x0001)
#define EFI_BROWSER_ACTION_DEFAULT_SAFE 0x1002 // Called on setting safe defaults (default value is equal 0x0002)
#define EFI_BROWSER_ACTION_DEFAULT_PLATFORM 0x2000 // Called on setting platform defaults (default values in range 0x4000-0x7fff)
#define EFI_BROWSER_ACTION_DEFAULT_HARDWARE 0x3000 // Called on setting hardware defaults (default values in range 0x8000-0xbfff)
#define EFI_BROWSER_ACTION_DEFAULT_FIRMWARE 0x4000 // Called on setting firmware defaults (default values in range 0xc000-0xffff)On each of these operations the Form Browser calls Callback() function for each of the form elements with the EFI_IFR_FLAG_CALLBACK flag.
To print EFI_BROWSER_ACTION value as a string we'll define this simple function:
EFI_STRING ActionToStr(EFI_BROWSER_ACTION Action)
{
switch (Action) {
case EFI_BROWSER_ACTION_CHANGING:
return L"EFI_BROWSER_ACTION_CHANGING";
case EFI_BROWSER_ACTION_CHANGED:
return L"EFI_BROWSER_ACTION_CHANGED";
case EFI_BROWSER_ACTION_RETRIEVE:
return L"EFI_BROWSER_ACTION_RETRIEVE";
case EFI_BROWSER_ACTION_FORM_OPEN:
return L"EFI_BROWSER_ACTION_FORM_OPEN";
case EFI_BROWSER_ACTION_FORM_CLOSE:
return L"EFI_BROWSER_ACTION_FORM_CLOSE";
case EFI_BROWSER_ACTION_SUBMITTED:
return L"EFI_BROWSER_ACTION_SUBMITTED";
case EFI_BROWSER_ACTION_DEFAULT_STANDARD:
return L"EFI_BROWSER_ACTION_DEFAULT_STANDARD";
case EFI_BROWSER_ACTION_DEFAULT_MANUFACTURING:
return L"EFI_BROWSER_ACTION_DEFAULT_MANUFACTURING";
case EFI_BROWSER_ACTION_DEFAULT_SAFE:
return L"EFI_BROWSER_ACTION_DEFAULT_SAFE";
case EFI_BROWSER_ACTION_DEFAULT_PLATFORM:
return L"EFI_BROWSER_ACTION_DEFAULT_PLATFORM";
case EFI_BROWSER_ACTION_DEFAULT_HARDWARE:
return L"EFI_BROWSER_ACTION_DEFAULT_HARDWARE";
case EFI_BROWSER_ACTION_DEFAULT_FIRMWARE:
return L"EFI_BROWSER_ACTION_DEFAULT_FIRMWARE";
default:
return L"Unknown";
}
}The EFI_QUESTION_ID type is defined in the https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Uefi/UefiInternalFormRepresentation.h
typedef UINT16 EFI_QUESTION_ID;
It is just a UINT16 value identificator to indicate for which of the form elements the Callback() function is called.
It is possible to explicitly set values for question id's of your form elements with the VFR questionid keyword. If you don't do it, the VfrCompiler will implicitly assign unique question identifiers to all the form elements without it. The numbering in this case starts from 0x0001.
The Form Browser also sends an actual form element data to the Callback() function.
But each element store the data in it's own type. Therefore the Form Browser in one argument sends the type of value https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Uefi/UefiInternalFormRepresentation.h:
//
// Types of the option's value.
//
#define EFI_IFR_TYPE_NUM_SIZE_8 0x00
#define EFI_IFR_TYPE_NUM_SIZE_16 0x01
#define EFI_IFR_TYPE_NUM_SIZE_32 0x02
#define EFI_IFR_TYPE_NUM_SIZE_64 0x03
#define EFI_IFR_TYPE_BOOLEAN 0x04
#define EFI_IFR_TYPE_TIME 0x05
#define EFI_IFR_TYPE_DATE 0x06
#define EFI_IFR_TYPE_STRING 0x07
#define EFI_IFR_TYPE_OTHER 0x08
#define EFI_IFR_TYPE_UNDEFINED 0x09
#define EFI_IFR_TYPE_ACTION 0x0A
#define EFI_IFR_TYPE_BUFFER 0x0B
#define EFI_IFR_TYPE_REF 0x0C
And in in another argument it sends the actual value as a union type:
typedef union {
UINT8 u8;
UINT16 u16;
UINT32 u32;
UINT64 u64;
BOOLEAN b;
EFI_HII_TIME time;
EFI_HII_DATE date;
EFI_STRING_ID string; ///< EFI_IFR_TYPE_STRING, EFI_IFR_TYPE_ACTION
EFI_HII_REF ref; ///< EFI_IFR_TYPE_REF
// UINT8 buffer[]; ///< EFI_IFR_TYPE_BUFFER
} EFI_IFR_TYPE_VALUE;
Therefore to get the actual value we first look at the UINT8 Type argument and then use the necessary type on the EFI_IFR_TYPE_VALUE union. Below I've written two functions: TypeToStr simply prints a type of the callback element, and DebugCallbackValue prints an element value based on it's type:
EFI_STRING TypeToStr(UINT8 Type)
{
switch (Type) {
case EFI_IFR_TYPE_NUM_SIZE_8:
return L"EFI_IFR_TYPE_NUM_SIZE_8";
case EFI_IFR_TYPE_NUM_SIZE_16:
return L"EFI_IFR_TYPE_NUM_SIZE_16";
case EFI_IFR_TYPE_NUM_SIZE_32:
return L"EFI_IFR_TYPE_NUM_SIZE_32";
case EFI_IFR_TYPE_NUM_SIZE_64:
return L"EFI_IFR_TYPE_NUM_SIZE_64";
case EFI_IFR_TYPE_BOOLEAN:
return L"EFI_IFR_TYPE_BOOLEAN";
case EFI_IFR_TYPE_TIME:
return L"EFI_IFR_TYPE_TIME";
case EFI_IFR_TYPE_DATE:
return L"EFI_IFR_TYPE_DATE";
case EFI_IFR_TYPE_STRING:
return L"EFI_IFR_TYPE_STRING";
case EFI_IFR_TYPE_OTHER:
return L"EFI_IFR_TYPE_OTHER";
case EFI_IFR_TYPE_UNDEFINED:
return L"EFI_IFR_TYPE_UNDEFINED";
case EFI_IFR_TYPE_ACTION:
return L"EFI_IFR_TYPE_ACTION";
case EFI_IFR_TYPE_BUFFER:
return L"EFI_IFR_TYPE_BUFFER";
case EFI_IFR_TYPE_REF:
return L"EFI_IFR_TYPE_REF";
default:
return L"Unknown";
}
}
VOID DebugCallbackValue(UINT8 Type, EFI_IFR_TYPE_VALUE *Value)
{
switch (Type) {
case EFI_IFR_TYPE_NUM_SIZE_8:
DEBUG ((EFI_D_INFO, "%d\n", Value->u8));
break;
case EFI_IFR_TYPE_NUM_SIZE_16:
DEBUG ((EFI_D_INFO, "%d\n", Value->u16));
break;
case EFI_IFR_TYPE_NUM_SIZE_32:
DEBUG ((EFI_D_INFO, "%d\n", Value->u32));
break;
case EFI_IFR_TYPE_NUM_SIZE_64:
DEBUG ((EFI_D_INFO, "%ld\n", Value->u64));
break;
case EFI_IFR_TYPE_BOOLEAN:
DEBUG ((EFI_D_INFO, "%d\n", Value->b));
break;
case EFI_IFR_TYPE_TIME:
DEBUG ((EFI_D_INFO, "%02d:%02d:%02d\n", Value->time.Hour, Value->time.Minute, Value->time.Second));
break;
case EFI_IFR_TYPE_DATE:
DEBUG ((EFI_D_INFO, "%04d/%02d/%02d\n", Value->date.Year, Value->date.Month, Value->date.Day));
break;
case EFI_IFR_TYPE_STRING:
if (Value->string)
DEBUG ((EFI_D_INFO, "%s\n", HiiGetString(mHiiHandle, Value->string, "en-US") ));
else
DEBUG ((EFI_D_INFO, "NO STRING!\n" ));
break;
default:
DEBUG ((EFI_D_INFO, "Unknown\n" ));
break;
}
}Let's get all of our helper functions and create a debug print statement for the Callback() code:
STATIC
EFI_STATUS
EFIAPI
Callback (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN EFI_BROWSER_ACTION Action,
IN EFI_QUESTION_ID QuestionId,
IN UINT8 Type,
IN OUT EFI_IFR_TYPE_VALUE *Value,
OUT EFI_BROWSER_ACTION_REQUEST *ActionRequest
)
{
DEBUG ((EFI_D_INFO, "Callback: Action=%s, QuestionId=0x%04x, Type=%s, Value=", ActionToStr(Action), QuestionId, TypeToStr(Type)));
DebugCallbackValue(Type, Value);
return EFI_UNSUPPORTED;
}Besides the Callback() let's add the DEBUG statements to the RouteConfig() and ExtractConfig() functions as well. This way we will know the order of how the Form Browser calls our functions:
STATIC
EFI_STATUS
EFIAPI
RouteConfig (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN CONST EFI_STRING Configuration,
OUT EFI_STRING *Progress
)
{
DEBUG ((EFI_D_INFO, "RouteConfig: Configuration=%s\n", Configuration));
...
}
STATIC
EFI_STATUS
EFIAPI
ExtractConfig (
IN CONST EFI_HII_CONFIG_ACCESS_PROTOCOL *This,
IN CONST EFI_STRING Request,
OUT EFI_STRING *Progress,
OUT EFI_STRING *Results
)
{
DEBUG ((EFI_D_INFO, "ExtractConfig: Request=%s\n", Request));
...
}
Now it is time to test our driver. Build our driver, copy it to the shared folder and run QEMU with debug log. For the last operation you can use the first stage of the run_gdb_ovmf.sh script:
./run_gdb_ovmf.sh -1
Load our driver to the UEFI shell.
FS0:\> load HIIFormCallbackDebug.efi
The Callback() code is run only by the Form Browser. Therefore if we would issue requests with our HIIConfig.efi application, the Callback() would never run. So let's type exit to run the Form Browser.
When we enter our form, the following strings would be printed to the debug log (by default the value for the numeric element is 8):
ExtractConfig: Request=GUID=927580373a731b4f9557f22af743e8c2&NAME=0046006f0072006d0044006100740061&PATH=01041400641982fbb4ac7b439fe666aa7ad7c5d87fff0400&OFFSET=0&WIDTH=0024
Callback: Action=EFI_BROWSER_ACTION_FORM_OPEN, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=0
Callback: Action=EFI_BROWSER_ACTION_RETRIEVE, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=8
As you see here our element got QuestionId=0x0002. This is because we didn't explicitly set any questionId's for our form elements and the numeric element is second on the form (the first is the checkbox element). We've set NUMERIC_SIZE_2 flag in the element VFR code, therefore the value is interpreted as Value->u16.
Change the numeric element value to 3:
Callback: Action=EFI_BROWSER_ACTION_CHANGING, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Callback: Action=EFI_BROWSER_ACTION_CHANGED, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
As you know, in this case the Form Browser doesn't call ExtractConfig/RouteConfig functions. But as you see you still have control in that case since the Callback() code is called.
Submit the form with updated value:
RouteConfig: Configuration=GUID=927580373a731b4f9557f22af743e8c2&NAME=0046006f0072006d0044006100740061&PATH=01041400641982fbb4ac7b439fe666aa7ad7c5d87fff0400&OFFSET=0000&WIDTH=0001&VALUE=00&OFFSET=0001&WIDTH=0002&VALUE=0003&OFFSET=0003&WIDTH=0014&VALUE=006f0072007000200067006e0069007200740053&OFFSET=0019&WIDTH=0004&VALUE=160507e5&OFFSET=001d&WIDTH=0003&VALUE=213717&OFFSET=0020&WIDTH=0001&VALUE=33&OFFSET=0021&WIDTH=0003&VALUE=0a0b0c
Callback: Action=EFI_BROWSER_ACTION_SUBMITTED, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Press reset to default button (this sets value to 7):
ExtractConfig: Request=GUID=927580373a731b4f9557f22af743e8c2&NAME=0046006f0072006d0044006100740061&PATH=01041400641982fbb4ac7b439fe666aa7ad7c5d87fff0400&OFFSET=0000&WIDTH=0001&OFFSET=0001&WIDTH=0002&OFFSET=0003&WIDTH=0014&OFFSET=0019&WIDTH=0004&OFFSET=001d&WIDTH=0003&OFFSET=0020&WIDTH=0001&OFFSET=0021&WIDTH=0003
Callback: Action=EFI_BROWSER_ACTION_DEFAULT_STANDARD, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Press reset to manufacture default button (this sets value to 8):
ExtractConfig: Request=GUID=927580373a731b4f9557f22af743e8c2&NAME=0046006f0072006d0044006100740061&PATH=01041400641982fbb4ac7b439fe666aa7ad7c5d87fff0400&OFFSET=0000&WIDTH=0001&OFFSET=0001&WIDTH=0002&OFFSET=0003&WIDTH=0014&OFFSET=0019&WIDTH=0004&OFFSET=001d&WIDTH=0003&OFFSET=0020&WIDTH=0001&OFFSET=0021&WIDTH=0003
Callback: Action=EFI_BROWSER_ACTION_DEFAULT_MANUFACTURING, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=7
Exit without submit
Callback: Action=EFI_BROWSER_ACTION_CHANGED, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Callback: Action=EFI_BROWSER_ACTION_FORM_CLOSE, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Here you see that 2 callbacks were executed: EFI_BROWSER_ACTION_CHANGED and EFI_BROWSER_ACTION_FORM_CLOSE. As another experiment enter the form again, set manufacture defaults and submit them. And only then exit our form. This way the exit action would print only the EFI_BROWSER_ACTION_FORM_CLOSE callback:
Callback: Action=EFI_BROWSER_ACTION_FORM_CLOSE, QuestionId=0x0002, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=8
So the EFI_BROWSER_ACTION_CHANGED in this case is called only if an element has unsubmitted changes.
In the last example the QuestionId for our element was set implicitly by the VfrCompiler. But as we've mentioned it earlier it is possible to set it yourself with a help of a quiestionid keyword.
For another experiment let's add INTERACTIVE flag to the checkbox and string elements. But set the quiestionid explicitly only for the checkbox and numeric elements:
...
checkbox
varid = FormData.CheckboxValue,
questionid = 0x5555,
prompt = STRING_TOKEN(CHECKBOX_PROMPT),
help = STRING_TOKEN(CHECKBOX_HELP),
flags = INTERACTIVE,
default = TRUE, defaultstore = StandardDefault,
default = FALSE, defaultstore = ManufactureDefault,
endcheckbox;
numeric
name = NumericQuestion,
varid = FormData.NumericValue,
questionid = 0x4444,
prompt = STRING_TOKEN(NUMERIC_PROMPT),
help = STRING_TOKEN(NUMERIC_HELP),
flags = NUMERIC_SIZE_2 | DISPLAY_UINT_HEX | INTERACTIVE,
minimum = 0,
maximum = 10,
step = 1,
default = 7, defaultstore = StandardDefault,
default = 8, defaultstore = ManufactureDefault,
endnumeric;
string
name = StringQuestion,
varid = FormData.StringValue,
prompt = STRING_TOKEN(STRING_PROMPT),
help = STRING_TOKEN(STRING_HELP),
flags = INTERACTIVE,
minsize = 5,
maxsize = 10,
default = STRING_TOKEN(STRING_DEFAULT), defaultstore = StandardDefault,
default = STRING_TOKEN(STRING_PROMPT), defaultstore = ManufactureDefault,
endstring
...
This would give us this output on the form open:
ExtractConfig: Request=GUID=927580373a731b4f9557f22af743e8c2&NAME=0046006f0072006d0044006100740061&PATH=01041400641982fbb4ac7b439fe666aa7ad7c5d87fff0400&OFFSET=0&WIDTH=0024
Callback: Action=EFI_BROWSER_ACTION_FORM_OPEN, QuestionId=0x5555, Type=EFI_IFR_TYPE_BOOLEAN, Value=0
Callback: Action=EFI_BROWSER_ACTION_FORM_OPEN, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=0
Callback: Action=EFI_BROWSER_ACTION_FORM_OPEN, QuestionId=0x0001, Type=EFI_IFR_TYPE_STRING, Value=
Callback: Action=EFI_BROWSER_ACTION_RETRIEVE, QuestionId=0x5555, Type=EFI_IFR_TYPE_BOOLEAN, Value=0
Callback: Action=EFI_BROWSER_ACTION_RETRIEVE, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=8
Callback: Action=EFI_BROWSER_ACTION_RETRIEVE, QuestionId=0x0001, Type=EFI_IFR_TYPE_STRING, Value=String pro
As you see here each action is called on every interactive form element. This is true for all other cases when the action affects all the form elements. This includes all the actions except EFI_BROWSER_ACTION_CHANGING and EFI_BROWSER_ACTION_CHANGED.
Another thing to point out is that the calls in the output above are happening not by the order of QuestionId's, but in the order of element placement in the VFR. Also as we've said it before, the VfrCompiler implicitly assigns QuestionId's to all the form elements which don't have any explicit setting for that. Even to those which don't have any INTERACTIVE flag. The implicit assignment starts from the 0x0001 value, and this is the value that our string element got.
Now if we change the numeric element value to 3, only numeric callback will be executed:
Callback: Action=EFI_BROWSER_ACTION_CHANGING, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
Callback: Action=EFI_BROWSER_ACTION_CHANGED, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=3
And if we exit the form without any submit, the following callbacks will be called:
Callback: Action=EFI_BROWSER_ACTION_CHANGED, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=8
Callback: Action=EFI_BROWSER_ACTION_FORM_CLOSE, QuestionId=0x5555, Type=EFI_IFR_TYPE_BOOLEAN, Value=0
Callback: Action=EFI_BROWSER_ACTION_FORM_CLOSE, QuestionId=0x4444, Type=EFI_IFR_TYPE_NUM_SIZE_16, Value=8
Callback: Action=EFI_BROWSER_ACTION_FORM_CLOSE, QuestionId=0x0001, Type=EFI_IFR_TYPE_STRING, Value=String pro
I hope all of these experiments have got you some understanding about when and how the Callback() function is executed.
To finish this lesson here is a logic diagram for an individual numeric element with the current value of 8:
Open form (even before the form is displayed)
EFI_BROWSER_ACTION_FORM_OPEN (Value=0)
EFI_BROWSER_ACTION_RETRIEVE (Value=8)
|
-------------------------------------------------
| |
Change value from 8 to 8 Close form
EFI_BROWSER_ACTION_CHANGING (Value=8) EFI_BROWSER_ACTION_FORM_CLOSE (Value=8)
|
-------------------------------------------------
| |
Change value from 8 to 9 Close form
EFI_BROWSER_ACTION_CHANGING (Value=9) EFI_BROWSER_ACTION_FORM_CLOSE (Value=8)
EFI_BROWSER_ACTION_CHANGED (Value=9)
|
-------------------------------------------------------------------------------------------------
| | |
Submit Close form with sumbit Close form without submit
EFI_BROWSER_ACTION_SUBMITTED (Value=9) EFI_BROWSER_ACTION_SUBMITTED (Value=9) EFI_BROWSER_ACTION_CHANGED (Value=8)
| EFI_BROWSER_ACTION_FORM_CLOSE (Value=9) EFI_BROWSER_ACTION_FORM_CLOSE (Value=8)
Close
EFI_BROWSER_ACTION_FORM_CLOSE (Value=9)