IOS View 背景颜色渐变--简单级别

 [self setContentMode:UIViewContentModeRedraw
//表示重新绘制界面 
==(calls -setNeedsDisplay)];
 CAGradientLayer *gradientLayer = [CAGradientLayer layer];
 gradientLayer.frame = self.bounds;
 gradientLayer.colors = [NSArray arrayWithObjects:(id)[[UIColor orangeColor] CGColor],
 (id)[[UIColor blueColor] CGColor],(id)[[UIColor whiteColor] CGColor],(id)[[UIColor brownColor] CGColor], nil];
 [self.layer insertSublayer:gradientLayer atIndex:0];