macOS NSView改变frame后会出现黑色残留，应付的办法是不在drawRect上修改重新initWithFrame一下就行

黑色部分就是残留。是因为绘制后保留了轨迹。

解决办法是不在drawRect中做处理重新写NSView，新增方法 initWithFrame

- (void)drawRect:(NSRect)dirtyRect {
    [super drawRect:dirtyRect];
    //cocoa方法的改变背景颜色
    [[NSColor redColor] setFill];
    NSRectFill(dirtyRect);
    // Drawing code here.
//    CGFloat lineWidth = 2.0;
//    // Drawing code here.
//    NSBezierPath* bgPath = [NSBezierPath bezierPathWithRoundedRect:NSInsetRect(dirtyRect, 10.0f, 10.0f) xRadius:3.0 yRadius:3.0];
//    [bgPath setLineWidth:lineWidth];
//    [bgPath setClip];
//    [[NSColor purpleColor] setFill];
//    [bgPath fill];
}

- (instancetype)initWithFrame:(NSRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setWantsLayer:YES];
        self.layer.backgroundColor = CGColorCreateGenericRGB(1.0, 0, 0, 1.0);
//        NSShadow *shadow = [[NSShadow alloc] init];
//        [shadow setShadowColor: [NSColor redColor]];
//        [shadow setShadowBlurRadius:4.0];
//        [self setShadow:shadow];

//        [self addSubview:self.klineVC.view];
//        [self.klineVC.view mas_makeConstraints:^(MASConstraintMaker *make) {
//            (void)make.edges;
//        }];
    }
    return self;
}

效果如图所示