delphi2010 Tlistview 怎么实现 虚拟加载分组
时间: 2024-03-09 18:49:50 浏览: 29
Delphi 2010 的 TListView 组件本身不支持虚拟加载和分组,但可以通过继承 TListView 实现这些功能。以下是实现虚拟加载和分组的示例代码:
```
unit VirtualListView;
interface
uses
ComCtrls;
type
TVirtualListViewItem = class(TListItem)
private
FLoaded: Boolean;
public
property Loaded: Boolean read FLoaded write FLoaded;
end;
TVirtualListViewGroup = class(TListGroup)
private
FLoaded: Boolean;
public
property Loaded: Boolean read FLoaded write FLoaded;
end;
TVirtualListView = class(TListView)
private
FVirtualItemCount: Integer;
FVirtualItemHeight: Integer;
FVirtualGroupCount: Integer;
FVirtualGroupHeaderHeight: Integer;
protected
function CreateItem(AOwner: TListItem): TListItem; override;
function CreateGroup(AOwner: TListGroup): TListGroup; override;
procedure DoUpdateItems(FirstIndex, LastIndex: Integer); override;
procedure DoUpdateGroups(FirstIndex, LastIndex: Integer); override;
function GetItemCount: Integer; override;
function GetItemHeight(AItem: TListItem): Integer; override;
function GetGroupHeaderHeight: Integer; override;
procedure SetVirtualItemCount(Value: Integer);
procedure SetVirtualItemHeight(Value: Integer);
procedure SetVirtualGroupCount(Value: Integer);
procedure SetVirtualGroupHeaderHeight(Value: Integer);
public
constructor Create(AOwner: TComponent); override;
property VirtualItemCount: Integer read FVirtualItemCount write SetVirtualItemCount;
property VirtualItemHeight: Integer read FVirtualItemHeight write SetVirtualItemHeight;
property VirtualGroupCount: Integer read FVirtualGroupCount write SetVirtualGroupCount;
property VirtualGroupHeaderHeight: Integer read FVirtualGroupHeaderHeight write SetVirtualGroupHeaderHeight;
end;
implementation
function TVirtualListView.CreateItem(AOwner: TListItem): TListItem;
begin
Result := TVirtualListViewItem.Create(Items);
end;
function TVirtualListView.CreateGroup(AOwner: TListGroup): TListGroup;
begin
Result := TVirtualListViewGroup.Create(Groups);
end;
procedure TVirtualListView.DoUpdateItems(FirstIndex, LastIndex: Integer);
var
I: Integer;
begin
for I := FirstIndex to LastIndex do
begin
if not Items[I].Loaded then
begin
Items[I].Loaded := True;
// 加载项目数据
end;
end;
end;
procedure TVirtualListView.DoUpdateGroups(FirstIndex, LastIndex: Integer);
var
I: Integer;
begin
for I := FirstIndex to LastIndex do
begin
if not Groups[I].Loaded then
begin
Groups[I].Loaded := True;
// 加载分组数据
end;
end;
end;
function TVirtualListView.GetItemCount: Integer;
begin
Result := FVirtualItemCount;
end;
function TVirtualListView.GetItemHeight(AItem: TListItem): Integer;
begin
Result := FVirtualItemHeight;
end;
function TVirtualListView.GetGroupHeaderHeight: Integer;
begin
Result := FVirtualGroupHeaderHeight;
end;
procedure TVirtualListView.SetVirtualItemCount(Value: Integer);
begin
FVirtualItemCount := Value;
Items.Count := Value;
end;
procedure TVirtualListView.SetVirtualItemHeight(Value: Integer);
begin
FVirtualItemHeight := Value;
end;
procedure TVirtualListView.SetVirtualGroupCount(Value: Integer);
begin
FVirtualGroupCount := Value;
Groups.Count := Value;
end;
procedure TVirtualListView.SetVirtualGroupHeaderHeight(Value: Integer);
begin
FVirtualGroupHeaderHeight := Value;
end;
constructor TVirtualListView.Create(AOwner: TComponent);
begin
inherited;
OwnerData := True;
end;
end.
```
在这个示例中,我们创建了两个新类:TVirtualListViewItem 和 TVirtualListViewGroup,它们分别继承自 TListItem 和 TListGroup,并增加了 Loaded 属性。这个属性用来标记项目或分组是否已经加载了数据。当项目或分组需要显示时,我们可以根据该属性来判断是否需要加载数据。
TVirtualListView 继承自 TListView,并重写了一些方法和属性。CreateItem 和 CreateGroup 方法分别创建 TVirtualListViewItem 和 TVirtualListViewGroup 对象。DoUpdateItems 和 DoUpdateGroups 方法分别在项目或分组需要显示时调用,用来加载数据。GetItemCount、GetItemHeight 和 GetGroupHeaderHeight 方法分别返回项目数、项目高度和分组标题高度。SetVirtualItemCount、SetVirtualItemHeight、SetVirtualGroupCount 和 SetVirtualGroupHeaderHeight 方法分别设置虚拟项目数、项目高度、虚拟分组数和分组标题高度。在 TVirtualListView 的构造函数中,我们将 OwnerData 属性设置为 True,这是启用虚拟模式的必要条件。
使用 TVirtualListView 时,可以像使用普通的 TListView 一样设置分组和项目,但需要设置虚拟属性。例如:
```
procedure TForm1.FormCreate(Sender: TObject);
begin
VirtualListView1.VirtualGroupCount := 100;
VirtualListView1.Groups[0].Header := 'Group 1';
VirtualListView1.Groups[1].Header := 'Group 2';
VirtualListView1.VirtualItemCount := 1000;
end;
```
在上面的示例中,我们设置了虚拟分组数和虚拟项目数。我们还设置了前两个分组的标题。当需要显示分组或项目时,TVirtualListView 会自动调用 DoUpdateGroups 和 DoUpdateItems 方法,来加载数据。
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