在drawRect中向UIView添加渐变 [英] adding gradient to UIView in drawRect

问题描述

   - （void）drawRect：在我的drawRect中添加一个CAGradientLayer，代码如下： （CGRect）rect {
 
 CAGradientLayer * gradientOverlay = [CAGradientLayer图层]; 
 CGColorRef grayColor = [UIColor colorWithRed：37 / 255.f green：37 / 255.f 
 blue：37 / 255.f alpha：1.0] .CGColor; 
 CGColorRef blueColor = [UIColor colorWithRed：23.0 / 255.0 green：171.0 / 255.0 
 blue：219.0 / 255.0 alpha：1.0] .CGColor; 
 gradientOverlay.colors = [NSArray arrayWithObjects：
（id）grayColor，
（id）grayColor，
（id）blueColor，
 nil]; 
 gradientOverlay.locations = [NSArray arrayWithObjects：
 [NSNumber numberWithFloat：0]，
 [NSNumber numberWithFloat：0.4]，
 [NSNumber numberWithFloat：1]，
 nil ]。 
 
 CGPoint startPoint = CGPointMake（CGRectGetMinX（rect），CGRectGetMidY（rect））; 
 CGPoint endPoint = CGPointMake（CGRectGetMaxX（rect），CGRectGetMidY（rect））; 
 
 gradientOverlay.startPoint = startPoint; 
 gradientOverlay.frame = self.bounds; 
 gradientOverlay.endPoint = endPoint; 
 
 self.layer.mask = gradientOverlay; 
 
} 
  

任何想法为什么这不起作用？

解决方案添加您的 CAGradientLayer 作为您的 self的子图层。层。
-
注意：如果您在 drawRect：方法中执行此操作，请确保您每次调用 drawRect：时，不添加新的 CAGradientLayer 。

 
 
  code> //创建一个保存背景图片的图层，并将其添加为self.layer的子图层
 CALayer * layer = [CALayer图层]; 
 layer.frame = self.layer.frame; 
 layer.contents =（id）[UIImage imageNamed：@background.png]。CGImage; 
 [self.layer addSublayer：layer]; 
 
 //创建您的CAGradientLayer 
 CAGradientLayer * gradientOverlay = [CAGradientLayer图层]; 
 CGColorRef grayColor = [UIColor colorWithRed：37 / 255.f green：37 / 255.f 
 blue：37 / 255.f alpha：1.0] .CGColor; 
 CGColorRef blueColor = [UIColor colorWithRed：23.0 / 255.0 green：171.0 / 255.0 
 blue：219.0 / 255.0 alpha：1.0] .CGColor; 
 gradientOverlay.colors = [NSArray arrayWithObjects：
（id）grayColor，
（id）grayColor，
（id）blueColor，
 nil]; 
 gradientOverlay.locations = [NSArray arrayWithObjects：
 [NSNumber numberWithFloat：0]，
 [NSNumber numberWithFloat：0.4]，
 [NSNumber numberWithFloat：1]，
 nil ]。 
 
 CGPoint startPoint = CGPointMake（CGRectGetMinX（rect），CGRectGetMidY（rect））; 
 CGPoint endPoint = CGPointMake（CGRectGetMaxX（rect），CGRectGetMidY（rect））; 
 
 gradientOverlay.startPoint = startPoint; 
 gradientOverlay.frame = self.layer.frame; 
 gradientOverlay.endPoint = endPoint; 
 //将其不透明度设置为0〜1 
 gradientOverlay.opacity = 0.6f; 
 //将它添加为self.layer的子图层（它将在背景图像
 [self.layer addSublayer：gradientOverlay]; 
  

注意：您不必在 drawRect：方法在 init 方法中创建图层层次结构，例如，如果需要更改某些视图/图层的几何图元，请覆盖 layoutSubviews 方法。

I am trying to add a CAGradientLayer in my drawRect, the code is the following:

- (void)drawRect:(CGRect)rect {

    CAGradientLayer *gradientOverlay = [CAGradientLayer layer];
    CGColorRef grayColor = [UIColor colorWithRed:37/255.f green:37/255.f 
                                            blue:37/255.f alpha:1.0].CGColor; 
    CGColorRef blueColor = [UIColor colorWithRed:23.0/255.0 green:171.0/255.0 
                                            blue:219.0/255.0 alpha:1.0].CGColor;
    gradientOverlay.colors = [NSArray arrayWithObjects:
                              (id) grayColor,
                              (id) grayColor,
                              (id) blueColor,
                              nil];
    gradientOverlay.locations = [NSArray arrayWithObjects:
                                 [NSNumber numberWithFloat:0],
                                 [NSNumber numberWithFloat:0.4],
                                 [NSNumber numberWithFloat:1],
                                 nil];

    CGPoint startPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMidY(rect));
    CGPoint endPoint = CGPointMake(CGRectGetMaxX(rect), CGRectGetMidY(rect));

    gradientOverlay.startPoint = startPoint;
    gradientOverlay.frame = self.bounds;
    gradientOverlay.endPoint = endPoint;

    self.layer.mask = gradientOverlay;

}

Any idea why this is not working?

解决方案

Add your CAGradientLayer as a sublayer of your self.layer.
Note: If you're doing it in the drawRect: method make sure you're not adding a new CAGradientLayer every time drawRect: is called.

UPDATE (regarding the comment): Here's the code for what you're asking:

    //Create a layer that holds your background image and add it as sublayer of your self.layer
    CALayer *layer = [CALayer layer];
    layer.frame = self.layer.frame;
    layer.contents = (id)[UIImage imageNamed:@"background.png"].CGImage;
    [self.layer addSublayer:layer];

//Create your CAGradientLayer
    CAGradientLayer *gradientOverlay = [CAGradientLayer layer];
    CGColorRef grayColor = [UIColor colorWithRed:37/255.f green:37/255.f 
                                            blue:37/255.f alpha:1.0].CGColor; 
    CGColorRef blueColor = [UIColor colorWithRed:23.0/255.0 green:171.0/255.0 
                                            blue:219.0/255.0 alpha:1.0].CGColor;
    gradientOverlay.colors = [NSArray arrayWithObjects:
                              (id) grayColor,
                              (id) grayColor,
                              (id) blueColor,
                              nil];
    gradientOverlay.locations = [NSArray arrayWithObjects:
                                 [NSNumber numberWithFloat:0],
                                 [NSNumber numberWithFloat:0.4],
                                 [NSNumber numberWithFloat:1],
                                 nil];

    CGPoint startPoint = CGPointMake(CGRectGetMinX(rect), CGRectGetMidY(rect));
    CGPoint endPoint = CGPointMake(CGRectGetMaxX(rect), CGRectGetMidY(rect));

    gradientOverlay.startPoint = startPoint;
    gradientOverlay.frame = self.layer.frame;
    gradientOverlay.endPoint = endPoint;
//set its opacity from 0 ~ 1
    gradientOverlay.opacity = 0.6f;
//add it as sublayer of self.layer (it will be over the layer with the background image
    [self.layer addSublayer:gradientOverlay];

Note: You don't have to do this in drawRect: method. Create your layer hierarchy in the init method for example, if you need to change the geometry of some views/layers override the layoutSubviews method.

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