问为什么我的NSPanel没有正常的灰色背景？

EN

(void)openPanel
{

NSLog(@"openPanel");

NSWindow *panel = self.panelController.window;

NSRect rect = [[[NSApp currentEvent] window] frame];
NSLog(@"rect.origin.x = %f",rect.origin.x);
NSLog(@"rect.origin.y = %f",rect.origin.y);
NSLog(@"rect.size.width = %f",rect.size.width);
NSLog(@"rect.size.height = %f",rect.size.height);
[panel setFrame:NSMakeRect(rect.origin.x, rect.origin.y-100, 200, 100) display:YES];
[NSApp activateIgnoringOtherApps:NO];
[panel makeKeyAndOrderFront:nil];

isPanelVisible = YES;
}