Cocoa 将NSTextView坐标转换为屏幕坐标

在我的应用程序中，我想在NSTextView中显示popover，并需要将NSTextView中所选矩形的坐标转换为屏幕坐标。我尝试过以下代码：

NSWindow* viewWindow = [self window];
NSRect rect = [self firstRectForCharacterRange:[self selectedRange]];
rect = [[self superview] convertRect:rect toView:nil]; //converting to NSClipView coordinate system
rect = [viewWindow convertRectToScreen:rect];
return rect;

它工作得几乎很好，但返回的rect已被“x”极大地“破坏”了原点。例如，如果开始时

rect.origin.x

为670，则最后等于1022

有什么想法吗

谢谢。

我知道了

- (NSRect)rectForPopover
{    
    NSRect rect = [self firstRectForCharacterRange:[self selectedRange]];
    NSRect txtViewBounds = [self convertRectToBacking:[self bounds]];
    txtViewBounds = [self.window convertRectToScreen:txtViewBounds];

    rect = [[self superview] convertRect:rect toView:nil];
    rect = [self.window convertRectToScreen:rect];

    rect.origin = NSMakePoint(rect.origin.x - txtViewBounds.origin.x - self.window.frame.origin.x, rect.origin.y);

    return rect;
}