delphi – TVirtualStringTree：OnMeasureItem事件和OnGetText事

OnMeasureItem for node 1
OnMeasureItem for node 2
OnMeasureItem for node 3
OnGetText for node 1
OnGetText for node 2
OnGetText for node 3

OnMeasureItem for node 1
OnGetText for node 1

OnMeasureItem for node 2
OnGetText for node 2

OnMeasureItem for node 3
OnGetText for node 3

procedure TMainForm.SyncHexLog;
begin
  HexLog.BeginUpdate;
  Try
    if (HexLog.RootNodeCount <> FirpList.ComOperationCountLagged) then
      begin
          HexLog.RootNodeCount := FirpList.ComOperationCountLagged;

          // measure for fast scrolling
          HexLog.ReInitNode(HexLog.GetLastNoInit(),True);    

          if FAutoScroll then
          begin
            HexLog.ScrollIntoView(HexLog.GetLast,False,False);
          end;
      end;
  Finally
    HexLog.EndUpdate;
  End;
end;

我会尝试通过从节点的状态中删除vsHeightMeasured并随后调用MeasureItemHeight方法来手动强制项目测量.它将再次触发OnMeasureItem.问题在于此处,因为您不应该多次测量项目的节点文本被更改,但仍然必须处理OnMeasureItem因为滚动的东西.

正如您在评论中提到的那样,您可以将自己的NodeMeasured标志包含到数据结构中,并在节点文本发生更改时(当日志项中的某些数据发生更改时)重置它,并在传递OnGetText事件后设置它.强制节点高度测量.这是一个伪代码：

procedure TForm1.VirtualStringTreeGetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: string);
begin
  ThreadList.LockList;
  try
    // check if the own flag which indicates that the text is new,that
    // the data has changed since the last time you were here in OnGetText
    // is False and if so,force the node measurement to set current node
    // height and set this flag to True to remember we already did this
    if not ThreadList.Items[Node.Index].NodeMeasured then
    begin
      // fake the node measurement,remove the measured flag
      Exclude(Node.States,vsHeightMeasured);
      // this will trigger the OnMeasureItem again because of removed
      // vsHeightMeasured flag from the node's state
      VirtualStringTree.MeasureItemHeight(VirtualStringTree.Canvas,Node);
      // set the NodeMeasured flag to remember we've measured the item
      ThreadList.Items[Node.Index].NodeMeasured := True;
    end;
    // here set the node's text and unlock your thread safe list
    CellText := ThreadList[Node.Index].SomeText;
  finally
    ThreadList.UnlockList;
  end;
end;

在数据发生变化的线程中,您必须将此NodeMeasured标志设置为False.

if LogHasChanged then
begin
  ThreadList.LockList;
  try
    ThreadList.Items[X].NodeMeasured := False;
    ThreadList.Items[X].SomeText := 'Something new';
  finally
    ThreadList.UnlockList;
  end;
end;