绘制渐变背景代码

- (void)drawRect:(NSRect)dirtyRect {

    [super drawRect:dirtyRect];

    NSGradient *backgroundGradient = [[NSGradient alloc] initWithStartingColor:[NSColor colorWithDeviceRed:239.0/255.0 green:239.0/255.0 blue:239.0/255.0 alpha:1.0] endingColor:[NSColor colorWithDeviceRed:239.0/255.0 green:239.0/255.0 blue:239.0/255.0 alpha:1.0]];

    [backgroundGradient drawInRect:[self bounds] angle:90.0];

    // Drawing code here.

}