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：

BOOL CenterWindow(HWND hWndCenter = NULL) throw()
...{


ATLASSERT(::IsWindow(m_hWnd));




// determine owner window to center against


DWORD dwStyle = GetStyle();


if(hWndCenter == NULL)




...{


if(dwStyle & WS_CHILD)


hWndCenter = ::GetParent(m_hWnd);


else


hWndCenter = ::GetWindow(m_hWnd, GW_OWNER);


}




// get coordinates of the window relative to its parent


RECT rcDlg;


::GetWindowRect(m_hWnd, &rcDlg);


RECT rcArea;


RECT rcCenter;


HWND hWndParent;


if(!(dwStyle & WS_CHILD))




...{


// don't center against invisible or minimized windows


if(hWndCenter != NULL)




...{


DWORD dwStyleCenter = ::GetWindowLong(hWndCenter, GWL_STYLE);


if(!(dwStyleCenter & WS_VISIBLE) || (dwStyleCenter & WS_MINIMIZE))


hWndCenter = NULL;


}




// center within screen coordinates


::SystemParametersInfo(SPI_GETWORKAREA, NULL, &rcArea, NULL);


if(hWndCenter == NULL)


rcCenter = rcArea;


else


::GetWindowRect(hWndCenter, &rcCenter);


}


else




...{


// center within parent client coordinates


hWndParent = ::GetParent(m_hWnd);


ATLASSERT(::IsWindow(hWndParent));




::GetClientRect(hWndParent, &rcArea);


ATLASSERT(::IsWindow(hWndCenter));


::GetClientRect(hWndCenter, &rcCenter);


::MapWindowPoints(hWndCenter, hWndParent, (POINT*)&rcCenter, 2);


}




int DlgWidth = rcDlg.right - rcDlg.left;


int DlgHeight = rcDlg.bottom - rcDlg.top;




// find dialog's upper left based on rcCenter


int xLeft = (rcCenter.left + rcCenter.right) / 2 - DlgWidth / 2;


int yTop = (rcCenter.top + rcCenter.bottom) / 2 - DlgHeight / 2;




// if the dialog is outside the screen, move it inside


if(xLeft < rcArea.left)


xLeft = rcArea.left;


else if(xLeft + DlgWidth > rcArea.right)


xLeft = rcArea.right - DlgWidth;




if(yTop < rcArea.top)


yTop = rcArea.top;


else if(yTop + DlgHeight > rcArea.bottom)


yTop = rcArea.bottom - DlgHeight;




// map screen coordinates to child coordinates


return ::SetWindowPos(m_hWnd, NULL, xLeft, yTop, -1, -1,


SWP_NOSIZE | SWP_NOZORDER | SWP_NOACTIVATE);


}