我正在尝试change the background color of a DateTimePicker ,但我的问题与我想做的事情无关。
我正在捕获窗口的 WM_PAINT
消息,让默认的绘图实现发生(即 ComCtrl.dll 中的实现),然后在其上进行绘制。
最初我的代码很简单:
TDateTimePicker = class(Vcl.ComCtrls.TDateTimePicker)
protected
procedure WMPaint(var Message: TMessage); message WM_PAINT;
end;
procedure TDateTimePicker.WMPaint(var Message: TMessage);
begin
inherited;
end;
我什么也没做,控件正常绘制:
现在乐趣开始
现在我将进行一些实际的绘图。这不是我想要的绘图,但它证明了它是有效的。我将在控件的矩形上绘制一个十字:
procedure TDateTimePicker.WMPaint(var Message: TMessage);
var
dc: HDC;
rc: TRect;
p: HPEN;
begin
inherited;
//Get the device context to scribble on
dc := GetDC(Self.Handle);
if dc = 0 then
Exit;
try
rc := Self.GetClientRect;
//Create a pen to draw a criss-cross
p := CreatePen(PS_SOLID, 0, ColorToRGB(clLime));
p := SelectObject(dc, p); //select the pen into the dc
Winapi.Windows.MoveToEx(dc, rc.Left, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Right, rc.Bottom);
Winapi.Windows.MoveToEx(dc, rc.Right, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Left, rc.Bottom);
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
finally
ReleaseDC(Self.Handle, dc);
end;
end;
这是非常简单的事情:
- 获取我们将在其上绘制的
HDC
- 获取控件的客户端矩形
- 创建一支实心红笔
- 选择笔进入DC
- 画十字
- 恢复旧笔
- 删除我们的笔
而且它有效!
当然有效。
现在填充整个矩形
我不想画十字,我想填充背景。首先,我将演示一种使用可怕的、可怕方法来实现我的目标的方法:
I will stroke the width of the control with a very thick pen
这是一件可怕的事情,但它具有实际工作的优点:
procedure TDateTimePicker.WMPaint(var Message: TMessage);
var
dc: HDC;
rc: TRect;
p: HPEN;
begin
inherited;
dc := GetDC(Self.Handle);
if dc = 0 then
Exit;
try
rc := Self.GetClientRect;
//Fill a rectangle using a pen (cause FillRect doesn't work)
p := CreatePen(PS_SOLID, rc.Height, ColorToRGB(clRed));
p := SelectObject(dc, p);
Winapi.Windows.MoveToEx(dc, rc.Left, (rc.Bottom+rc.Top) div 2, nil); //middle of left edge
Winapi.Windows.LineTo(dc, rc.Right, (rc.Bottom+rc.Top) div 2); //middle of right edge
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
//Create a pen to draw a criss-cross
p := CreatePen(PS_SOLID, 0, ColorToRGB(clLime));
p := SelectObject(dc, p); //select the pen into the dc
Winapi.Windows.MoveToEx(dc, rc.Left, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Right, rc.Bottom);
Winapi.Windows.MoveToEx(dc, rc.Right, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Left, rc.Bottom);
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
finally
ReleaseDC(Self.Handle, dc);
end;
end;
这是非常简单的事情:
- 创建一支 23 像素高的笔
- 从左到右抚过选择器的整个宽度
它有效:
当然有效!
但我不想消灭一切
我不想删除日期时间选择器中的所有内容,只想删除“客户端”区域。所以我调整了矩形:
- 从顶部、左侧和底部减去 2 个像素
- 从日期时间选择器下拉按钮的右边缘减去 34 个像素
带有代码片段:
rc := Self.GetClientRect;
//rc := GetRectOfThePartIWant;
rc.Left := 2;
rc.Top := 2;
rc.Bottom := rc.Bottom-2;
rc.Right := rc.Right-34; //button width is 34 (use DateTime_GetDateTimePickerInfo.rcButton)
//Fill a rectangle using a pen (cause FillRect doesn't work)
//p := CreatePen(PS_SOLID, rc.Height, ColorToRGB(clRed));
br := Default(TLogBrush);
br.lbStyle := BS_SOLID;
br.lbColor := ColorToRGB($00CCCCFF);
br.lbHatch := 0; //ignored for a BS_SOLID brush
p := ExtCreatePen(PS_SOLID or PS_GEOMETRIC or PS_ENDCAP_FLAT, rc.Height, br, 0, nil);
if p <> 0 then
begin
p := SelectObject(dc, p);
Winapi.Windows.MoveToEx(dc, rc.Left, (rc.Bottom+rc.Top) div 2, nil); //middle of left edge
Winapi.Windows.LineTo(dc, rc.Right, (rc.Bottom+rc.Top) div 2); //middle of right edge
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
end;
它有效:
当然有效!
FillRect 有什么问题吗?
最初我只是使用了FillRect
,只不过它坚持只用白色绘制;而不是任何颜色:
procedure TDateTimePicker.WMPaint(var Message: TMessage);
var
dc: HDC;
rc: TRect;
br: TLogBrush;
b: HBRUSH;
le: Integer;
p: HPEN;
begin
inherited;
dc := GetDC(Self.Handle);
if dc = 0 then
Exit;
try
rc := Self.GetClientRect;
b := CreateSolidBrush(ColorToRGB(clRed));
if b <> 0 then
begin
b := SelectObject(dc, b); //select the brush into the DC
if b <> 0 then
begin
le := FillRect(dc, rc, b);
if le = 0 then
begin
//Draw failed
if IsDebuggerPresent then
DebugBreak;
end;
SelectObject(dc, b); //restore the old brush
end;
DeleteObject(b);
end;
//Create a pen to draw a criss-cross
p := CreatePen(PS_SOLID, 0, ColorToRGB(clLime));
p := SelectObject(dc, p); //select the pen into the dc
Winapi.Windows.MoveToEx(dc, rc.Left, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Right, rc.Bottom);
Winapi.Windows.MoveToEx(dc, rc.Right, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Left, rc.Bottom);
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
finally
ReleaseDC(Self.Handle, dc);
end;
end;
它不起作用:
当然不行。它试图让我的生活变得困难。如果它有效的话我就不用花 9 个小时在上面了。
我尝试只填充矩形的上半部分;确保我的来源是正确的:
rc := Self.GetClientRect;
rc2 := rc;
rc2.Bottom := (rc2.Top + rc2.Bottom) div 2;
b := CreateSolidBrush(ColorToRGB(clRed));
if b <> 0 then
begin
b := SelectObject(dc, b); //select the brush into the DC
if b <> 0 then
begin
le := FillRect(dc, rc2, b);
if le = 0 then
begin
//Draw failed
if IsDebuggerPresent then
DebugBreak;
end;
SelectObject(dc, b); //restore the old brush
end;
DeleteObject(b);
end;
//Create a pen to draw a criss-cross
p := CreatePen(PS_SOLID, 0, ColorToRGB(clLime));
p := SelectObject(dc, p); //select the pen into the dc
Winapi.Windows.MoveToEx(dc, rc.Left, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Right, rc.Bottom);
Winapi.Windows.MoveToEx(dc, rc.Right, rc.Top, nil);
Winapi.Windows.LineTo(dc, rc.Left, rc.Bottom);
P := SelectObject(dc, p); //restore old pen
DeleteObject(p); //delete our pen
它不起作用:
当然不行。
为什么不起作用?
为什么不起作用?
奖金闲聊
您无法使用 Delphi 样式引擎,because the Styles Engine is not enabled when using Windows themes (仅当使用自定义主题时)。
最佳答案
b := CreateSolidBrush(ColorToRGB(clRed));
if b <> 0 then
begin
b := // *** original brush gets overwritten here ***
SelectObject(dc, b); //select the brush into the DC
if b <> 0 then
begin
le := FillRect(dc, rc, b);
您不需要将画笔选择到设备上下文中,因为您将其作为参数传递。然后选择它,将返回的值分配回画笔变量,然后使用错误的画笔参数执行FillRect
(这就是它不起作用的原因)。
关于delphi - 为什么当 LineTo 成功时 FillRect 不绘制?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29519335/