Alpha并没有改变UINavigationBar的barTintColor

Question

我想将UINavigationBar的颜色设置为黑色，使用alpha 0.6来查看我的界面。但如果我使用这段代码：

self.navigationController?.navigationBar.barTintColor = UIColor(red: 0/255, green: 0/255, blue: 0/255, alpha: 0.6)
self.navigationController?.navigationBar.translucent = true

它仍然看起来像alpha 1.0：

如何使用黑色透明色透明？

由于

Answer 1

您必须使用相同的颜色设置navgationBar的背景图像，而不是设置barTintColor。请在此处查看类似的问题：

I can't set UINavigationBar's barTintColor to clearColor successfully

但是你必须得到这种特殊颜色的图像。你可以将这个图像放到你的项目中，然后使用

        let image = UIImage(named: "yourimage'name")

获取图片。

或者您可以向视图控制器添加一个func：

 func imageFromColor(color:UIColor,size:CGSize)->UIImage{
    let rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContext(rect.size);
    let context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextFillRect(context, rect);

    var image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIGraphicsBeginImageContext(size)
    image.drawInRect(rect)
    image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image;
}

并在viewdidload中调用此函数：

    let color=UIColor(red: 0, green: 0, blue: 0, alpha: 0.6)
    let image=imageFromColor(color, size: CGSizeMake(1, 1))

    self.navigationController?.navigationBar.translucent=true;
    self.navigationController?.navigationBar.setBackgroundImage(image, forBarMetrics: UIBarMetrics.Default)

这样可行。

Answer 2

斯威夫特3：

func imageFromColor(color: UIColor, size: CGSize) -> UIImage {
    let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    UIGraphicsBeginImageContext(rect.size)
    let context = UIGraphicsGetCurrentContext()

    context!.setFillColor(color.cgColor)
    context!.fill(rect)

    var image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    UIGraphicsBeginImageContext(size)
    image?.draw(in: rect)
    image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image!
}

作为UIColor扩展程序

extension UIColor {
    func toImage(withSize size: CGSize) -> UIImage {
        let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
        UIGraphicsBeginImageContext(rect.size)
        let context = UIGraphicsGetCurrentContext()

        context!.setFillColor(self.cgColor)
        context!.fill(rect)

        var image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        UIGraphicsBeginImageContext(size)
        image?.draw(in: rect)
        image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image!
    }
}

Answer 3

您必须从Color获取图像，因为较低的iOS版本存在一些问题。使用此方法将您的UIColor转换为背景图像。

Xmarin.iOS

private static UIImage GetImageFromColor(UIColor color, CGSize size)
            {
                var rect = new CGRect(0, 0, size.Width, size.Height);
                UIGraphics.BeginImageContextWithOptions(size, false, 0);
                color.SetFill();
                UIGraphics.RectFill(rect);
                var image = UIGraphics.GetImageFromCurrentImageContext();
                UIGraphics.EndImageContext();
                return image;
            }

调用此方法

var bgImage = GetImageFromColor（UIColor.FromRGBA（r，g，b，alpha），new CGSize（viewWidth，viewHeight））;