delphi - 使用 OnDrawItem 事件时未正确绘制 TListview

Question

我在 TlistView 组件中使用 OnDrawItem 事件来使用自定义颜色绘制内容，但是当滚动列表视图时会出现一些工件。

这是使用的代码。

procedure TForm35.FormCreate(Sender: TObject);
var
 i, j : integer;
 Item : TListItem;
 s : string;
begin
  for i:= 0 to 99 do
  begin
    Item:=ListView1.Items.Add;
    for j:= 0 to ListView1.Columns.Count-1 do
    begin
      s:= Format('Row %d Column %d',[i+1, j+1]);
      if j=0 then
       Item.Caption :=s
      else
       Item.SubItems.Add(s);
    end;
  end;
end;

procedure TForm35.ListView1DrawItem(Sender: TCustomListView; Item: TListItem;
  Rect: TRect; State: TOwnerDrawState);
var
  x, y, i: integer;
begin
  if odSelected in State then
  begin
    TListView(Sender).Canvas.Brush.Color := clYellow;
    TListView(Sender).Canvas.Font.Color := clBlack;
  end
  else
  begin
    TListView(Sender).Canvas.Brush.Color := clLtGray;
    TListView(Sender).Canvas.Font.Color := clGreen;
  end;

  TListView(Sender).Canvas.FillRect(Rect);
  x := 5;
  y := (Rect.Bottom - Rect.Top - TListView(Sender).Canvas.TextHeight('Hg')) div 2 + Rect.Top;
  TListView(Sender).Canvas.TextOut(x, y, Item.Caption);
  for i := 0 to Item.SubItems.Count - 1 do
  begin
    inc(x, TListView(Sender).Columns[i].Width);
    TListView(Sender).Canvas.TextOut(x, y, Item.SubItems[i]);
  end;
end;

我在 Delphi 2007 和 XE3 中测试了这段代码，但得到了相同的结果。我怎样才能防止这个问题？

Answer 1

好的。更改X := 5为X := Rect.Left;

还有另一种解决方案（可能更准确）：

uses
    Graphics;

//... Form or something else declarations ... 

implementation

procedure TForm35.ListView1DrawItem(Sender: TCustomListView; Item: TListItem; Rect: TRect; State: TOwnerDrawState);
var
    s: string;
    ts: TTextStyle; // Text style (used for drawing)
begin
    // inherited;
    // Clear target rectangle
    // Set Canvas'es Font, Pen, Brush according for Item state
    // Get into s variable text value of the Cell.
    ts.Alignment := taLeftJustify; // Horz left alignment
    ts.Layout := tlCenter;         // Vert center alignment
    ts.EndEllipsis := True;        // End ellipsis (...) If line of text is too long too fit between left and right boundaries
    // Other fields see in the Graphics.TTextStyle = packed record 
    ListView1.Canvas.TextRect(
        Rect, 
        Rect.Left, // Not sure, but there are a small chance of this values equal to zero instead of Rect...
        Rect.Top, 
        s, 
        ts)
end;

end.

为了防止一些轻弹...

...
var
    b: TBitmap;
begin
    b := TBitmap.Create;
    try
        b.Widht := Rect.Right - Rect.Left;
        b.Height := Rect.Bottom - Rect.Top;
        //...
        // Draw content on the b.Canvas
        //...
        ListView.Canvas.Draw(Rect.Left, Rect.Top, b);
    finally
        b.Free;
    end;
end;