add subLayer to a imageView.layer

问题:

well I know that every imageViews have a layer (we can access it with :imageView.layer).I would like to use the layer of my imageView and add a subLayer to it's layer:shapeLayer(that is a CAShapeLayer) My code doesn't work, it doesn't show the shape layer!

- (void)viewDidLoad 
{
   imageView = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
   [self.view addSubview:imageView];
}

- (void)anotherMethod
{
   [imageView.layer addSublayer:shapeLayer];
}

How can I solve this please ?

回答1:

Try this:

[outputImage.layer insertSublayer:shapeLayer atIndex:0];

回答2:

I solved similar problem by using UIView below UIImageView and setting a layer to UIView. When you add a layer to UIImageView at index 0, your image will not be visible.

I have a UIView called photoView. It has a subview of class UIImageView, that has same bounds and has a clear background color. And I add a gradientLayer to photoView.

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Adding gradient background to UIImageView
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.photoImageView.bounds;
    gradientLayer.colors = @[(id)[UIColor customUltraLightGrayColor].CGColor, (id)[UIColor customUltraLightGrayColor].CGColor, (id)[UIColor customDarkGrayColor].CGColor];
    gradientLayer.locations = @[@(0.0), @(0.6)];
    [self.photoView.layer insertSublayer:gradientLayer atIndex:0];
}

As a result I get this:

回答3:

This could have several reasons, for example:

• Did you #import <QuartzCore/QuartzCore.h> (and / or CoreGraphics/CoreGraphics.h> depending on what you are doing in the rest of your code)?

• You could have set a wrong CGRectMake when initializing the CALayer which is not inside your visible frame (Like CGRectMake(5000,5000,...,...)) or one of the size properties is 0?

回答4:

Try setting the frame for layer: Follow the three steps

CALayer layerToBeAdded = [[CALayer alloc] init];
[layerToBeAdded setFrame:imgView.frame];
[imgView.layer addSublayer:layerToBeAdded];

Instead of allocating CALayer, you can use [imgView layer]

And to add image to layer do it like this

layerToBeAdded.contents = (id)imgXYZ.CGImage; 

回答5:

Assuming that you are talking about just one UIImageView (imageView == outputImage ???)

//in another method:
{
    [imageView.layer addSublayer:shapeLayer]; //Where is outputImage initialized?
}

回答6:

Here is a solution:

CALayer *pulseLayer_ = [[CALayer layer] retain];
pulseLayer_.backgroundColor = [[UIColor whiteColor] CGColor];
pulseLayer_.bounds = CGRectMake(0., 0., 80., 80.);
pulseLayer_.cornerRadius = 12.;
pulseLayer_.position = self.view.center;
[self.view.layer addSublayer:pulseLayer_];
CALayer *imageLayer = [CALayer layer];
imageLayer.frame = pulseLayer_.bounds;
imageLayer.cornerRadius = 10.0;
imageLayer.contents = (id) [UIImage imageNamed:@"jacklogo.png"].CGImage;
imageLayer.masksToBounds = YES;
[pulseLayer_ addSublayer:imageLayer];
[pulseLayer_ setNeedsDisplay];