设置WPF窗口相对于非WPF窗口的位置

在前一个Post当中，指出了在WPF的WindowInteropHelper类中的一个BUG：通过WindowInteropHelper的Owner属性不能实现把WPF窗口的Owner属性设置为一个非WPF窗口的句柄。

在我的Post帖出后不到一天，在WPF SDK的Blog上，就针对这个BUG给出了一个非常完美的解决方案。既然不同通过设置WindowStartupLocation.CenterOwner来改变窗口的位置。那么我们就用WindowStartupLocation.Manual来手动计算设置窗口的位置。大致的代码如下：

using System.Windows;
using System.Windows.Interop; // WindowInteropHelper

...

// Instantiate the owned WPF window
Window cw = new Window();

// Set the owned WPF window’s owner with the non-WPF owner window
IntPtr ownerWindowHandle = ...;

// Set the owned WPF window’s owner with the non-WPF owner window

WindowInteropHelper helper = new WindowInteropHelper(cw);
helper.Owner = ownerWindowHandle;

// Manually calculate Top/Left to appear centered
int nonWPFOwnerLeft = ...; // Get non-WPF owner’s Left
int nonWPFOwnerWidth = ...; // Get non-WPF owner’s Width
int nonWPFOwnerTop = ...; // Get non-WPF owner’s Top
int nonWPFOwnerHeight = ...; // Get non-WPF owner’s Height

cw.WindowStartupLocation = WindowStartupLocation.Manual;
cw.Left = nonWPFOwnerLeft + (nonWPFOwnerWidth - cw.Width) / 2;
cw.Top = nonWPFOwnerTop + (nonWPFOwnerHeight - cw.Height) / 2;

// Show the owned WPF window
cw.Show();

这段代码理论上没有什么问题呢？但是WPF是支持设备独立的。因此，在非WPF Owner窗口的某些情况下可能会因为DPI的而不能正常工作。解决这个问题，可以利用HwndSource类进行窗口位置的设备独立计算：

using System.Windows; // Window, WindowStartupLocation, Point
using System.Windows.Interop; // WindowInteropHelper, HwndSource
using System.Windows.Media; // Matrix

...

// Instantiate the owned WPF window
CenteredWindow cw = new CenteredWindow();

// Get the handle to the non-WPF owner window
IntPtr ownerWindowHandle = ...; // Get hWnd for non-WPF window

// Set the owned WPF window’s owner with the non-WPF owner window
WindowInteropHelper helper = new WindowInteropHelper(cw);
helper.Owner = ownerWindowHandle;

// Center window
// Note - Need to use HwndSource to get handle to WPF owned window,
// and the handle only exists when SourceInitialized has been
// raised

cw.SourceInitialized += delegate
{
// Get WPF size and location for non-WPF owner window
int nonWPFOwnerLeft = ...; // Get non-WPF owner’s Left
int nonWPFOwnerWidth = ...; // Get non-WPF owner’s Width
int nonWPFOwnerTop = ...; // Get non-WPF owner’s Top
int nonWPFOwnerHeight = ...; // Get non-WPF owner’s Height

// Get transform matrix to transform non-WPF owner window
// size and location units into device-independent WPF
// size and location units

HwndSource source = HwndSource.FromHwnd(helper.Handle);
if (source == null) return;
Matrix matrix = source.CompositionTarget.TransformFromDevice;
Point ownerWPFSize = matrix.Transform(
new Point(nonWPFOwnerWidth, nonWPFOwnerHeight));
Point ownerWPFPosition = matrix.Transform(
new Point(nonWPFOwnerLeft, nonWPFOwnerTop));

// Center WPF window
cw.WindowStartupLocation = WindowStartupLocation.Manual;
cw.Left = ownerWPFPosition.X + (ownerWPFSize.X - cw.Width) / 2;
cw.Top = ownerWPFPosition.Y + (ownerWPFSize.Y - cw.Height) / 2;

};

// Show WPF owned window
cw.Show();

在上面的代码中需要注意的是HwndSource的使用。这个类需要一个窗口句柄，因此它的代码被放在一个SourceInitialized的事件委派函数中执行。

最后，除了上面这种方法，其实我们还可以用Win32 API函数来实现，在ATL的CWindow类中，就有这样的一个函数，我直接把放在下面，有兴趣的朋友参考其中的实现原理：

BOOLCenterWindow(HWNDhWndCenter = NULL) throw ()
... {
ATLASSERT(::IsWindow(m_hWnd));

//determineownerwindowtocenteragainst
DWORDdwStyle=GetStyle();
if(hWndCenter==NULL)
...{
if(dwStyle&WS_CHILD)
hWndCenter=::GetParent(m_hWnd);
else
hWndCenter=::GetWindow(m_hWnd,GW_OWNER);
}

//getcoordinatesofthewindowrelativetoitsparent
RECTrcDlg;
::GetWindowRect(m_hWnd,&rcDlg);
RECTrcArea;
RECTrcCenter;
HWNDhWndParent;
if(!(dwStyle&WS_CHILD))
...{
//don'tcenteragainstinvisibleorminimizedwindows
if(hWndCenter!=NULL)
...{
DWORDdwStyleCenter=::GetWindowLong(hWndCenter,GWL_STYLE);
if(!(dwStyleCenter&WS_VISIBLE)||(dwStyleCenter&WS_MINIMIZE))
hWndCenter=NULL;
}

//centerwithinscreencoordinates
::SystemParametersInfo(SPI_GETWORKAREA,NULL,&rcArea,NULL);
if(hWndCenter==NULL)
rcCenter=rcArea;
else
::GetWindowRect(hWndCenter,&rcCenter);
}
else
...{
//centerwithinparentclientcoordinates
hWndParent=::GetParent(m_hWnd);
ATLASSERT(::IsWindow(hWndParent));

::GetClientRect(hWndParent,&rcArea);
ATLASSERT(::IsWindow(hWndCenter));
::GetClientRect(hWndCenter,&rcCenter);
::MapWindowPoints(hWndCenter,hWndParent,(POINT*)&rcCenter,2);
}

intDlgWidth=rcDlg.right-rcDlg.left;
intDlgHeight=rcDlg.bottom-rcDlg.top;

//finddialog'supperleftbasedonrcCenter
intxLeft=(rcCenter.left+rcCenter.right)/2-DlgWidth/2;
intyTop=(rcCenter.top+rcCenter.bottom)/2-DlgHeight/2;

//ifthedialogisoutsidethescreen,moveitinside
if(xLeft<rcArea.left)
xLeft=rcArea.left;
elseif(xLeft+DlgWidth>rcArea.right)
xLeft=rcArea.right-DlgWidth;

if(yTop<rcArea.top)
yTop=rcArea.top;
elseif(yTop+DlgHeight>rcArea.bottom)
yTop=rcArea.bottom-DlgHeight;

//mapscreencoordinatestochildcoordinates
return::SetWindowPos(m_hWnd,NULL,xLeft,yTop,-1,-1,
SWP_NOSIZE|SWP_NOZORDER|SWP_NOACTIVATE);
}