MAknsSkinInstance::GetCachedItemData() return NuLL

核心提示：MAknsSkinInstance::GetCachedItemData() return NuLLIDTSS000716Creation dateJuly 4, 2007PlatformS60 3rd EditionS60 3rd Edition, FP1DevicesCategorySymbian C++Subca

MAknsSkinInstance::GetCachedItemData() return NuLL

IDTSS000716Creation dateJuly 4, 2007

PlatformS60 3rd Edition

S60 3rd Edition, FP1Devices

CategorySymbian C++SubcategoryUI, Scalable UI

Keywords (APIs, classes, methods, functions):

Overview

Why does MAknsSkinInstance::GetCachedItemData() return NULL?

Description

The skin server in S60 provides a way to construct a bitmap (CFbsBitmap) of default skin elements.

The bitmap is typically obtained from the skin as follows:

#include

MAknsSkinInstance* skin = AknsUtils::SkinInstance();

CAknsItemData* skinItem = skin->GetCachedItemData( someUID, EAknsITBitmap );

if( skinItem != NULL )

{

CFbsBitmap* bitmap = static_cast(skinItem)->Bitmap();

}

The above approach works fine for skin items that are bitmaps (EAknsITBitmap) or masked bitmaps (EAknsITMaskedBitmap). However, this is not true for all skin items. For example, if someUID in the above code is set to one of the following values:

KAknsIIDQsnBgAreaMainIdle,

KAknsIIDQsnBgScreenIdle,

KAknsIIDQsnBgScreen

GetCachedItemData() would return NULL as these UIDs do not correspond to bitmaps, but to items of type EAknsITEffectQueue.

If a skinnable element in a theme is of type EAknsITEffectQueue, it means that the item supports effects. Effects are one of the main features of scalable UI. When a skin item supports effects, it means that the item can have multiple layers. Each layer can be an image or it can be image/pixel manipulation scheme that acts on previous layer(s). The effects may be programmed to change over time, and even the first (background) layer can refer to another skin