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()
}