iOS中為控件設置顏色漸變和透明度漸變

項目中用到地圖設置漸變色，查找資料找到兩種方法：一種設置顏色，一種設置透明度；

//為顏色設置漸變效果：

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];

    CAGradientLayer *gradient = [CAGradientLayer layer];

    //設置開始和結束位置(設置漸變的方向)

    gradient.startPoint = CGPointMake(0, 0);

    gradient.endPoint = CGPointMake(1, 0);

    gradient.frame =CGRectMake(0,0,40,40);

    gradient.colors = [NSArray arrayWithObjects:(id)[UIColor redColor].CGColor,(id)[UIColorwhiteColor].CGColor,nil];

    [view.layer insertSublayer:gradient atIndex:0];

    [self.view addSubview:view];

    

    //為透明度設置漸變效果

    UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];

    UIColor *colorOne = [UIColor colorWithRed:(216/255.0)  green:(0/255.0)  blue:(18/255.0)  alpha:1.0];

    UIColor *colorTwo = [UIColor colorWithRed:(216/255.0)  green:(0/255.0)  blue:(18/255.0)  alpha:0.0];

    NSArray *colors = [NSArray arrayWithObjects:(id)colorOne.CGColor, colorTwo.CGColor, nil];

    CAGradientLayer *gradient = [CAGradientLayer layer];

    //設置開始和結束位置(設置漸變的方向)

    gradient.startPoint = CGPointMake(0, 0);

    gradient.endPoint = CGPointMake(1, 0);

    gradient.colors = colors;

    gradient.frame = CGRectMake(0, 0, 40, 40);

    [view.layerinsertSublayer:gradientatIndex:0];

    [self.view addSubview:view];