Loading FireMonkey style resources with RTTI - delphi

Question

I am trying to write class that inherits from FMX TStyledControl. When style is updated it loads style resource objects to cache.
I created project group for package with custom controls and test FMX HD project as it describes in Delphi help. After installing package and placing TsgSlideHost on the test form I run test app. It works well, but when I close it and try to rebuild package RAD Studio says “Error in rtl160.bpl” or “invalid pointer operation”.
It seems what problem in LoadToCacheIfNeeded procedure from TsgStyledControl, but I’m not understand why. Is there any restriction on using RTTI with FMX styles or anything?
TsgStyledControl sources:
unit SlideGUI.TsgStyledControl;
interface
uses
System.SysUtils, System.Classes, System.Types, FMX.Types, FMX.Layouts, FMX.Objects,
FMX.Effects, System.UITypes, FMX.Ani, System.Rtti, System.TypInfo;
type
TCachedAttribute = class(TCustomAttribute)
private
fStyleName: string;
public
constructor Create(const aStyleName: string);
property StyleName: string read fStyleName;
end;
TsgStyledControl = class(TStyledControl)
private
procedure CacheStyleObjects;
procedure LoadToCacheIfNeeded(aField: TRttiField);
protected
function FindStyleResourceAs<T: class>(const AStyleLookup: string): T;
function GetStyleName: string; virtual; abstract;
function GetStyleObject: TControl; override;
public
procedure ApplyStyle; override;
published
{ Published declarations }
end;
implementation
{ TsgStyledControl }
procedure TsgStyledControl.ApplyStyle;
begin
inherited;
CacheStyleObjects;
end;
procedure TsgStyledControl.CacheStyleObjects;
var
ctx: TRttiContext;
typ: TRttiType;
fld: TRttiField;
begin
ctx := TRttiContext.Create;
try
typ := ctx.GetType(Self.ClassType);
for fld in typ.GetFields do
LoadFromCacheIfNeeded(fld);
finally
ctx.Free
end;
end;
function TsgStyledControl.FindStyleResourceAs<T>(const AStyleLookup: string): T;
var
fmxObj: TFmxObject;
begin
fmxObj := FindStyleResource(AStyleLookup);
if Assigned(fmxObj) and (fmxObj is T) then
Result := fmxObj as T
else
Result := nil;
end;
function TsgStyledControl.GetStyleObject: TControl;
var
S: TResourceStream;
begin
if (FStyleLookup = '') then
begin
if FindRCData(HInstance, GetStyleName) then
begin
S := TResourceStream.Create(HInstance, GetStyleName, RT_RCDATA);
try
Result := TControl(CreateObjectFromStream(nil, S));
Exit;
finally
S.Free;
end;
end;
end;
Result := inherited GetStyleObject;
end;
procedure TsgStyledControl.LoadToCacheIfNeeded(aField: TRttiField);
var
attr: TCustomAttribute;
styleName: string;
styleObj: TFmxObject;
val: TValue;
begin
for attr in aField.GetAttributes do
begin
if attr is TCachedAttribute then
begin
styleName := TCachedAttribute(attr).StyleName;
if styleName <> '' then
begin
styleObj := FindStyleResource(styleName);
val := TValue.From<TFmxObject>(styleObj);
aField.SetValue(Self, val);
end;
end;
end;
end;
{ TCachedAttribute }
constructor TCachedAttribute.Create(const aStyleName: string);
begin
fStyleName := aStyleName;
end;
end.
Using of TsgStyledControl:
type
TsgSlideHost = class(TsgStyledControl)
private
[TCached('SlideHost')]
fSlideHost: TLayout;
[TCached('SideMenu')]
fSideMenuLyt: TLayout;
[TCached('SlideContainer')]
fSlideContainer: TLayout;
fSideMenu: IsgSideMenu;
procedure ReapplyProps;
procedure SetSideMenu(const Value: IsgSideMenu);
protected
function GetStyleName: string; override;
function GetStyleObject: TControl; override;
procedure UpdateSideMenuLyt;
public
constructor Create(AOwner: TComponent); override;
procedure ApplyStyle; override;
published
property SideMenu: IsgSideMenu read fSideMenu write SetSideMenu;
end;

Answer 1

Using TRttiField.GetAttributes leads to errors in design-time. It's a bug in Delphi XE2. See QC Report.