How to apply transparency in Android color

来源:互联网 时间:1970-01-01

13 Oct 2015

Today I was chatting with my friend Andres Galante about colors in Android. He was about to send some colors for a developer team's use in an Android app and asked me: Can you use rgba for the greys or they must be hex?

The short answer is:

You can use the [Android Color util method argb :

Color.argb(alpha, r, g, b);

But... it's not common. Android developers usually set colors as a resource in XML file and unfortunelly XML resource not accept RGB only HEX

/res/values/color.xml

<color name="textColor">#FFFFFF</color>

So, He told me: the problem is Material Design has specific opacity rules for text, icons, and dividers . How we apply it using HEX ?

Well, It's not a problem, because Android uses Hex ARGB values , which are formatted as #AARRGGB

The first pair of letters (AA), represent the Alpha. You must convert your decimal opacity values to a Hexdecimal value. Here are the steps:

Take your opacity as a decimal value and multiply it by 255. So, if you have a block that is 50% opaque the decimal value would be .5. For example: .5 x 255 = 127.5 The fraction won't convert to hex, so you must round your number up or down to the nearest whole number. For example: 127.5 rounds up to 128; 55.25 rounds down to 55. Enter your decimal value in a decimal to hexadecimal converter, like this http://www.binaryhexconverter.com/decimal-to-hex-converter, and convert your values If you only get back a single value, prefix it with a zero. For example, if you're trying to get 5% opacity and your going through this process you'll end up with the hex value of D. Add a zero in front of it so it appears as 0D.

Source: Alpha Hex Value Process

/res/values/color.xml

<!-- Black text color with 87% of opacity --><color name="textColor">#DE000000</color>

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