Subclassing NSView to have a transparent background

问题

I am creating an app where I need to have a transparent NSView with a transparent PNG image inside. The problem is, the NSView I'm drawing has a gray background on it. I have it subclassed (as TransparentRectangleView) but don't know what to put in drawRect to make it transparent.

I have already overridden the isOpaque method to return NO but it doesn't seem to help...

Alternatively, is there already a subclassed NSView that is similar to the iPhone's UIImageView (as long as I can add subviews inside, I need to add some text inside).

回答1:

To make a view transparent, simply fill it with [NSColor clearColor].

- (void)drawRect:(NSRect)rect {
    [[NSColor clearColor] set];
    NSRectFill(rect);
}

The default implementation of isOpaque returns NO, so if you are subclassing NSView and not some other view you don't need to worry about overriding it.

回答2:

The accepted answer does not work for me since mine window is opaque. As http://www.drissman.com/blog/archives/2009/10/09/nsrectfill_and_nscolor_clearcolor.html (and the discussion below) said, the following codes work:

- (void)drawRect:(NSRect)rect {
    [[NSColor clearColor] set];
    NSRectFillUsingOperation(rect, NSCompositeSourceOver);
    // do other drawings
}

回答3:

The Swift version:

override func draw(_ dirtyRect: NSRect) {

    NSColor.clear.set()
    dirtyRect.fill()
}

来源：https://stackoverflow.com/questions/4635442/subclassing-nsview-to-have-a-transparent-background