无法 select 虚拟树视图中的根节点
Cannot select the root node in Virtual Tree View
我正在使用带有虚拟树视图的 Delphi XE3。
我的代码如下:
type
TMyData = record
Caption: string;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
RootNode: PVirtualNode;
PData: ^TMyData;
begin
RootNode := tvItems.AddChild(nil);
PData := tvItems.GetNodeData(RootNode);
PData^.Caption := 'This is a test node';
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
tvItems.NodeDataSize := SizeOf(TMyData);
end;
procedure TForm1.tvItemsGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
var
PData: ^TMyData;
begin
if Assigned(Node) then
begin
PData := tvItems.GetNodeData(Node);
if Assigned(PData) then
Celltext := PData^.Caption;
end;
end;
当我点击"Button1"时,根节点将被创建。但是,当我的鼠标点击节点文本时,它不会被 selected.
我的一些发现:
必须单击节点文本的开头才能 select 节点。如果单击节点文本的中间或末尾,则不会select编辑该节点。
如果我将 tvItemsGetText 更改为以下,则问题消失:
procedure TForm1.tvItemsGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
var
PData: ^TMyData;
begin
CellText := 'This is a test node';
end;
我在tvItemsGetText中设置了一个断点,发现它会被调用多次。前几次,PData 将为 nil,这使得 CellText 为空。在最后一次调用时,PData 将生效并且 CellText 将设置为 'This is a test node'.
看来允许鼠标点击的范围和select节点是由节点的初始文本决定的。如果初始文本为空字符串,则必须在节点的最开始单击才能select它。
这是虚拟树视图的错误吗?
有几种方法可以通过用户数据初始化新节点。
1。使用 OnInitNode
事件:
procedure TForm5.Button1Click(Sender: TObject);
begin
vt1.InsertNode(nil, amAddChildLast); // internal calls vt1InitNode
end;
procedure TForm5.vt1InitNode(Sender: TBaseVirtualTree; ParentNode, Node: PVirtualNode;
var InitialStates: TVirtualNodeInitStates);
var
PData: ^TMyData;
begin
PData := Sender.GetNodeData(Node);
PData^.Caption := 'This is a test node';
end;
2 使用 UserData
参数
变体 1. 动态数据
不要忘记删除 InitNode
事件并且不要设置 NodeDataSize
属性
type
TMyData = record
Caption: string;
end;
PMyData = ^TMyData;
procedure TForm5.Button1Click(Sender: TObject);
var
p: PMyData;
begin
New(p);
p.Caption:='This is a test node';
vt1.InsertNode(nil, amAddChildLast, p); // create node with initialized user data
// by default VirtualTree use NodeDataSize = SizeOf(pointer),
// so there is no reason to use GetNodeDataSize event
end;
procedure TForm5.vt1GetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
PData: PMyData;
begin
if Assigned(Node) then
begin
PData := PMyData(Sender.GetNodeData(Node)^); // little modification
// for correct access to dynamic node data
if Assigned(PData) then
CellText := PData.Caption;
end;
end;
procedure TForm5.vt1FreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
var
p: PMyData;
begin
p:=PMyData(Sender.GetNodeData(Node)^);
Dispose(p); // as you allocate memory for user data - you should free it to avoid memory leaks
end;
变体 2.对象
向您的表单添加新的私有函数:
private
{ Private declarations }
function GetObjectByNode<T: class>(Node: PVirtualNode): T;
// do not forget to include System.Generics.Collections to `uses`
实现:
function TForm5.GetObjectByNode<T>(Node: PVirtualNode): T;
var
NodeData: Pointer;
tmpObject: TObject;
begin
Result := nil;
if not Assigned(Node) then
exit;
NodeData := vt1.GetNodeData(Node);
if Assigned(NodeData) then
tmpObject := TObject(NodeData^);
if tmpObject is T then
Result := T(tmpObject)
else
Result := nil;
end;
以及主要代码(几乎与变体 1 相同):
procedure TForm5.Button1Click(Sender: TObject);
var
d: TMyData;
begin
d := TMyData.Create;
d.Caption := 'This is a test node';
vt1.InsertNode(nil, amAddChildLast, d);
end;
procedure TForm5.vt1FreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
var
d: TMyData;
begin
d := GetObjectByNode<TMyData>(Node);
d.Free;
end;
procedure TForm5.vt1GetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
d: TMyData;
begin
d := GetObjectByNode<TMyData>(Node);
if Assigned(d) then
CellText := d.Caption;
end;
我正在使用带有虚拟树视图的 Delphi XE3。
我的代码如下:
type
TMyData = record
Caption: string;
end;
procedure TForm1.Button1Click(Sender: TObject);
var
RootNode: PVirtualNode;
PData: ^TMyData;
begin
RootNode := tvItems.AddChild(nil);
PData := tvItems.GetNodeData(RootNode);
PData^.Caption := 'This is a test node';
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
tvItems.NodeDataSize := SizeOf(TMyData);
end;
procedure TForm1.tvItemsGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
var
PData: ^TMyData;
begin
if Assigned(Node) then
begin
PData := tvItems.GetNodeData(Node);
if Assigned(PData) then
Celltext := PData^.Caption;
end;
end;
当我点击"Button1"时,根节点将被创建。但是,当我的鼠标点击节点文本时,它不会被 selected.
我的一些发现:
必须单击节点文本的开头才能 select 节点。如果单击节点文本的中间或末尾,则不会select编辑该节点。
如果我将 tvItemsGetText 更改为以下,则问题消失:
procedure TForm1.tvItemsGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
var
PData: ^TMyData;
begin
CellText := 'This is a test node';
end;
我在tvItemsGetText中设置了一个断点,发现它会被调用多次。前几次,PData 将为 nil,这使得 CellText 为空。在最后一次调用时,PData 将生效并且 CellText 将设置为 'This is a test node'.
看来允许鼠标点击的范围和select节点是由节点的初始文本决定的。如果初始文本为空字符串,则必须在节点的最开始单击才能select它。
这是虚拟树视图的错误吗?
有几种方法可以通过用户数据初始化新节点。
1。使用 OnInitNode
事件:
procedure TForm5.Button1Click(Sender: TObject);
begin
vt1.InsertNode(nil, amAddChildLast); // internal calls vt1InitNode
end;
procedure TForm5.vt1InitNode(Sender: TBaseVirtualTree; ParentNode, Node: PVirtualNode;
var InitialStates: TVirtualNodeInitStates);
var
PData: ^TMyData;
begin
PData := Sender.GetNodeData(Node);
PData^.Caption := 'This is a test node';
end;
2 使用 UserData
参数
变体 1. 动态数据
不要忘记删除 InitNode
事件并且不要设置 NodeDataSize
属性
type
TMyData = record
Caption: string;
end;
PMyData = ^TMyData;
procedure TForm5.Button1Click(Sender: TObject);
var
p: PMyData;
begin
New(p);
p.Caption:='This is a test node';
vt1.InsertNode(nil, amAddChildLast, p); // create node with initialized user data
// by default VirtualTree use NodeDataSize = SizeOf(pointer),
// so there is no reason to use GetNodeDataSize event
end;
procedure TForm5.vt1GetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
PData: PMyData;
begin
if Assigned(Node) then
begin
PData := PMyData(Sender.GetNodeData(Node)^); // little modification
// for correct access to dynamic node data
if Assigned(PData) then
CellText := PData.Caption;
end;
end;
procedure TForm5.vt1FreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
var
p: PMyData;
begin
p:=PMyData(Sender.GetNodeData(Node)^);
Dispose(p); // as you allocate memory for user data - you should free it to avoid memory leaks
end;
变体 2.对象
向您的表单添加新的私有函数:
private
{ Private declarations }
function GetObjectByNode<T: class>(Node: PVirtualNode): T;
// do not forget to include System.Generics.Collections to `uses`
实现:
function TForm5.GetObjectByNode<T>(Node: PVirtualNode): T;
var
NodeData: Pointer;
tmpObject: TObject;
begin
Result := nil;
if not Assigned(Node) then
exit;
NodeData := vt1.GetNodeData(Node);
if Assigned(NodeData) then
tmpObject := TObject(NodeData^);
if tmpObject is T then
Result := T(tmpObject)
else
Result := nil;
end;
以及主要代码(几乎与变体 1 相同):
procedure TForm5.Button1Click(Sender: TObject);
var
d: TMyData;
begin
d := TMyData.Create;
d.Caption := 'This is a test node';
vt1.InsertNode(nil, amAddChildLast, d);
end;
procedure TForm5.vt1FreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
var
d: TMyData;
begin
d := GetObjectByNode<TMyData>(Node);
d.Free;
end;
procedure TForm5.vt1GetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
Column: TColumnIndex; TextType: TVSTTextType;
var CellText: string);
var
d: TMyData;
begin
d := GetObjectByNode<TMyData>(Node);
if Assigned(d) then
CellText := d.Caption;
end;