Adjust alpha of UIColor

Question

I set a UIColor using rgb to a background of a UILabel. I'm trying to adjust the alpha only. How can I modify the alpha of an existing rgb UIColor?

Edit

Basically I have UILabels that have a set UIColor (using rgb), and I won't know what color the UILabels are. At a certain point, I will have to change the labels alpha`. How can I just change the labels color alpha?

Of a predefined `UIColor`? For a label you could use the `.alpha` property. — LinusGeffarth, Jun 19 '15 at 05:02
Thanks for the response!. I have a predefined UIColor. I don't want to set the labels alpha, but the colors alpha — Eric, Jun 19 '15 at 05:04

score 206 · Answer 1 · edited Mar 23 '17 at 08:41

206

colorWithAlphaComponent: did the trick.

So what I had to do was:

self.mylabel.backgroundColor = [self.myLabel.backgroundColor colorWithAlphaComponent:0.3];

edited Mar 23 '17 at 08:41

pkamb

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answered Jun 19 '15 at 05:55

Eric

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is there any difference between this approach and say this? `UIColor(red:0.07, green:0.44, blue:0.54, alpha:0.4)` – Changerrs Sep 18 '17 at 17:58
2

@Changerrs : there can be cases when we need to apply alpha to a existing color. ie existing colors cant not be modified. Hence for such cases we already have a color value, but then need to apply alpha to it hence colorWithAlphaComponent comes handy for such case. – Bishal Ghimire Dec 10 '17 at 03:42

score 106 · Answer 2 · edited Oct 08 '20 at 11:16

106

Swift 3+

yourUIView.backgroundColor = UIColor.white.withAlphaComponent(0.75)

Swift 2

yourUIView.backgroundColor = UIColor.whiteColor().colorWithAlphaComponent(0.75)

edited Oct 08 '20 at 11:16

Yoav

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answered Apr 01 '16 at 14:11

GraSim

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score 15 · Answer 3 · answered Dec 18 '16 at 07:46

15

If you have custom colors defined, you can do this as well:

view.backgroundColor = [[MyClass someColor] colorWithAlphaComponent:0.25];

answered Dec 18 '16 at 07:46

chris g

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JZAU · Answer 4 · 2015-06-19T05:10:24.123

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why not using label.alpha = 0.5 ? to adjust your label's alpha?

update: if you want to adjust alpha from a old color, here is an example:

UIColor uicolor = [UIColor greenColor];
CGColorRef color = [uicolor CGColor];

int numComponents = CGColorGetNumberOfComponents(color);

UIColor newColor;
if (numComponents == 4)
{
    const CGFloat *components = CGColorGetComponents(color);
    CGFloat red = components[0];
    CGFloat green = components[1];
    CGFloat blue = components[2];
    newColor = [UIColor colorWithRed: red green: green blue: blue alpha: YOURNEWALPHA];

}

edited Jun 19 '15 at 05:10

answered Jun 19 '15 at 05:03

JZAU

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I don't want to set the labels alpha, I want to set the labels color alpha – Eric Jun 19 '15 at 05:03
Where's the difference? – LinusGeffarth Jun 19 '15 at 05:04
If I set the alpha of the whole label, then the text will also become lighter because I'm setting the background color of the label – Eric Jun 19 '15 at 05:06
@Eric Do you means change color's alpha from an existing UIColor? – JZAU Jun 19 '15 at 05:20

score 10 · Answer 5 · answered Nov 25 '20 at 04:58

10

Version Swift (5.4)

UIColor.blue.withAlphaComponent(0.5)

answered Nov 25 '20 at 04:58

Peter Suwara

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score 5 · Answer 6 · answered Jun 28 '21 at 04:46

5

The shortest possible code (Swift 5):

view.backgroundColor = .black.withAlphaComponent(0.75)

answered Jun 28 '21 at 04:46

Ethan Allen

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Santu C · Answer 7 · 2015-06-19T05:09:07.547

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Please set alpha in below code -

[UIColor colorWithRed:200.0/255.0 green:191.0/255.0 blue:231.0 /255.0 alpha:1.0]

edited Jun 19 '15 at 05:09

answered Jun 19 '15 at 05:04

Santu C

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I have that code, but I want to modify the alpha only – Eric Jun 19 '15 at 05:05
you want to set background color of UIlabel and want to change alpha of UILabel right ? Please use above code – Santu C Jun 19 '15 at 05:08
[UIColor colorWithRed:200.0/255 green:191.0/255 blue:231.0/255 alpha:1.0] modify like that – Arun Jun 19 '15 at 05:08
Yes Right , sorry by mistake – Santu C Jun 19 '15 at 05:08

Adjust alpha of UIColor

7 Answers7