CALayer未显示 [英] CALayer not displaying

问题描述

所以这是我第一次尝试使用CALayer.构建成功，并且没有报告的错误，因此我认为我必须做的事情显然是错误的.但是该图层根本不显示.

So this is my first ever attempt at using a CALayer. Build is successful and no reported bugs, so I assume I must be doing something obviously wrong. But the layer does not display at all.

- (void)viewDidLoad
{

    // Get Reliant Magenta in amazingly verbose manner
    CGColorSpaceRef rgbaColorSpace      = CGColorSpaceCreateDeviceRGB();
    CGFloat reliantMagentaValues[4]     = {(208/255),(27/255),(124/255),0.3f};
    CGColorRef reliantMagenta           = CGColorCreate(rgbaColorSpace, reliantMagentaValues);

    CALayer *reliantCanvasLayer         = [CALayer layer];

    reliantCanvasLayer.backgroundColor  = reliantMagenta;
    reliantCanvasLayer.frame            = CGRectMake(0, 0, 640, 960);

    [super viewDidLoad];

    [[[self view] layer] addSublayer:reliantCanvasLayer];

    CGColorRelease(reliantMagenta);

}

我得到了一整张洋红色的图片，而不是一整页的洋红色.我如何弄乱这么简单的东西?

Instead of a full page of magenta, I get back an empty view of grey. How am I messing up something this simple?

更新

- (void)viewDidLoad
{

    [super viewDidLoad];

    // Get Reliant Magenta in amazingly verbose manner
    CGColorSpaceRef rgbaColorSpace      = CGColorSpaceCreateDeviceRGB();
    CGFloat reliantMagentaValues[4]     = {(208/255),(27/255),(124/255),0.3f};
    CGColorRef reliantMagenta           = CGColorCreate(rgbaColorSpace, reliantMagentaValues);

    [[self view] layer].backgroundColor   = reliantMagenta;

    CGColorRelease(reliantMagenta);

}

相同的问题，但是视图现在是黑色的，并且不显示在情节提要中添加的元素

same problem, but view is now black and not displaying elements added in the storyboard

推荐答案

一个问题(可能是唯一的问题)是您要创建具有全部零个成分的颜色.当您说 208/255 时，编译器将使用整数执行除法运算并除去余数，因此 208/255 为0.您需要在浮点数中进行除法: 208.0f/255.0f .

One problem (possibly the only problem) is that you're creating your color with all zero components. When you say 208/255, the compiler performs the division using integers and drops the remainder, so 208/255 is 0. You need to divide in floating point: 208.0f / 255.0f.

使用 UIColor 代替自己设置 CGColorSpace 和 CGColor 也容易得多.试试这个:

It's also much easier to use a UIColor instead of setting up the CGColorSpace and the CGColor yourself. Try this:

- (void)viewDidLoad {
    [super viewDidLoad];

    UIColor *reliantMagenta = [UIColor colorWithRed:208.0f / 255.0f
        green:27.0f / 255.0f blue:124.0f / 255.0f alpha:0.3f];

    CALayer *magentaLayer = [CALayer layer];
    magentaLayer.frame = CGRectMake(0, 0, 640, 960);
    magentaLayer.backgroundColor = reliantMagenta.CGColor;

    [self.view.layer addSublayer:magentaLayer];
}

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