ShadowCircle.m

- (void)drawRect:(CGRect)rect {
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    UIGraphicsPushContext(ctx);
    CGContextSetRGBFillColor(ctx, 1.0f, 1.0f, 1.0f, 1.0f);  // white color
    CGContextSetShadow(ctx, CGSizeMake(2.0f, 2.0f), 2.0f); //也可以使用CGContextSetShadowWithColor (myContext, myShadowOffset, 5, myColor);
    CGContextFillEllipseInRect(ctx, CGRectMake(10.0f, 10.0f, 100.0f, 100.0f));  // a white filled circle with a diameter of 100 pixels, centered in (60, 60)
    UIGraphicsPopContext();
}