Can drag webview to move window in cococa?

1. 问题

如果cococa程序，在一个==没有titlebar==的window里只有一个webview，是否能够==拖曳这个webview来拖动整个window==呢？当然，直接拖是不行的，webview会先接受这个拖曳drag事件。

对于window中除webview以外的其他控件，其实可以直接重载NSWindow的mouseDown和mouseDragged方法来实现要的效果，但是webview不行，它需要另外重载NSWindow的sendEvent来实现mouse事件的额外操作。

另外，需要注意的是没有titlebar的window，相当于[self.window setStyleMask:(NSBorderlessWindowMask)].对于使用NSBorderlessWindowMask这个’Window Style Masks’时，需要额外实现canBecomeKeyWindow or canBecomeMainWindow返回YES，从而让这
个window成为当前主窗口。Apple官方文档对此的说明如下：

The window displays none of the usual peripheral elements. Useful only for display or caching purposes. A window that uses NSBorderlessWindowMask can’t become key or main, unless you implement canBecomeKeyWindow or canBecomeMainWindow to return YES. Note that you can set a window’s or panel’s style mask to NSBorderlessWindowMask in Interface Builder by deselecting Title Bar in the Appearance section of the Attributes inspector.

2. 代码

将现有window设置成下面这个BorderlessWindow即可。

.h文件：

#import 

@interface BorderlessWindow : NSWindow

@end

.m文件

#import "BorderlessWindow.h"

@interface BorderlessWindow()

@property (assign) NSPoint initialLocation;

@end

@implementation BorderlessWindow

- (BOOL)canBecomeKeyWindow
{
    return YES;
}

- (BOOL)canBecomeMainWindow
{
    return YES;
}

- (void)sendEvent:(NSEvent *)theEvent
{
    if ([theEvent type] == NSLeftMouseDown)
    {
        [self mouseDown:theEvent];
    }
    else if ([theEvent type] == NSLeftMouseDragged)
    {
        [self mouseDragged:theEvent];
    }

    [super sendEvent:theEvent];
}

- (void)mouseDown:(NSEvent *)theEvent
{
    self.initialLocation = [theEvent locationInWindow];
}

- (void)mouseDragged:(NSEvent *)theEvent
{
    NSPoint currentLocation;
    NSPoint newOrigin;

    NSRect  screenFrame = [[NSScreen mainScreen] frame];
    NSRect  windowFrame = [self frame];

    currentLocation = [NSEvent mouseLocation];
    newOrigin.x = currentLocation.x - self.initialLocation.x;
    newOrigin.y = currentLocation.y - self.initialLocation.y;

    // Don't let window get dragged up under the menu bar
    if( (newOrigin.y+windowFrame.size.height) > (screenFrame.origin.y+screenFrame.size.height) ){
        newOrigin.y=screenFrame.origin.y + (screenFrame.size.height-windowFrame.size.height);
    }

    //go ahead and move the window to the new location
    [self setFrameOrigin:newOrigin];
}

3. 参考

• [stackoverflow]Make WebView from WebKit draggable by mouse in Cocoa
• [stackoverflow]Can I move window using an object inside that window?