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unit VTAccessibilityFactory;
// class to create IAccessibles for the tree passed into it.
// If not already assigned, creates IAccessibles for the tree itself
// and the focused item
// the tree accessible is returned when the tree receives an WM_GETOBJECT message
// the AccessibleItem is returned when the Accessible is being asked for the first child
// To create your own IAccessibles, use the VTStandardAccessible unit as a reference,
// and assign your Accessibles to the variables in tthe unit's initialization.
// You only need to add the unit to your project, and voil, you have an accessible string tree!
//
// Written by Marco Zehe. (c) 2007
interface
uses
Classes, oleacc, VirtualTrees;
type
IVTAccessibleProvider = interface
function CreateIAccessible(ATree: TBaseVirtualTree): IAccessible;
end;
TVTAccessibilityFactory = class(TObject)
private
FAccessibleProviders: TInterfaceList;
public
constructor Create;
destructor Destroy; override;
function CreateIAccessible(ATree: TBaseVirtualTree): IAccessible;
procedure RegisterAccessibleProvider(AProvider: IVTAccessibleProvider);
procedure UnRegisterAccessibleProvider(AProvider: IVTAccessibleProvider);
end;
var
VTAccessibleFactory: TVTAccessibilityFactory;
implementation
{ TVTAccessibilityFactory }
constructor TVTAccessibilityFactory.Create;
begin
inherited;
FAccessibleProviders := TInterfaceList.Create;
FAccessibleProviders.Clear;
end;
function TVTAccessibilityFactory.CreateIAccessible(
ATree: TBaseVirtualTree): IAccessible;
var
I: Integer;
TmpIAccessible: IAccessible;
// returns an IAccessible.
// 1. If the Accessible property of the passed-in tree is nil,
// the first registered element will be returned.
// Usually, this is the IAccessible that provides information about the tree itself.
// If it is not nil, we'll check whether the AccessibleItem is nil.
// If it is, we'll look in the registered IAccessibles for the appropriate one.
// Each IAccessibleProvider will check the tree for properties to determine whether it is responsible.
// We'll work top to bottom, from the most complicated to the most simple.
// The index for these should all be greater than 0, e g the IAccessible for the tree itself should always be registered first, then any IAccessible items.
begin
result := nil;
if ATree <> nil then
begin
if ATree.Accessible = nil then
begin
if FAccessibleProviders.Count > 0 then
begin
result := IVTAccessibleProvider(FAccessibleProviders.Items[0]).CreateIAccessible(ATree);
exit;
end;
end;
if ATree.AccessibleItem = nil then
begin
if FAccessibleProviders.Count > 0 then
begin
for I := FAccessibleProviders.Count - 1 downto 1 do
begin
TmpIAccessible := IVTAccessibleProvider(FAccessibleProviders.Items[I]).CreateIAccessible(ATree);
if TmpIAccessible <> nil then
begin
result := TmpIAccessible;
break;
end;
end;
if TmpIAccessible = nil then
begin
result := IVTAccessibleProvider(FAccessibleProviders.Items[0]).CreateIAccessible(ATree);
end;
end;
end
else begin
result := ATree.AccessibleItem;
end;
end;
end;
destructor TVTAccessibilityFactory.Destroy;
begin
FAccessibleProviders.Free;
FAccessibleProviders := nil;
inherited;
end;
procedure TVTAccessibilityFactory.RegisterAccessibleProvider(
AProvider: IVTAccessibleProvider);
// Ads a provider if it is not already registered
begin
if FAccessibleProviders.IndexOf(AProvider) < 0 then
FAccessibleProviders.Add(AProvider)
end;
procedure TVTAccessibilityFactory.UnRegisterAccessibleProvider(
AProvider: IVTAccessibleProvider);
// Unregisters/removes an IAccessible provider if it is present
begin
if FAccessibleProviders.IndexOf(AProvider) >= 0 then
FAccessibleProviders.Remove(AProvider);
end;
end.
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