颜色渐变效果

    self.lineView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 200, 100)];
    [self.view addSubview:self.lineView];
    
    UIColor * firstColor = [UIColor redColor];
    UIColor * lastColor = [UIColor purpleColor];
    
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.colors = @[(__bridge id)firstColor.CGColor, (__bridge id)lastColor.CGColor];
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(0, 1);
    gradientLayer.frame = CGRectMake(0, 0, 200, 100);;
    [_lineView.layer addSublayer:gradientLayer];