How to make a background 20% transparent on Androi

2019-01-01 07:26发布

How do I make the background of a Textview about 20% transparent (not fully transparent), where there is a color in the background (i.e. white)?

14条回答
残风、尘缘若梦
2楼-- · 2019-01-01 08:00

See screenshot

I have taken three Views. In the first view I set full (no alpha) color, on the second view I set half (0.5 alpha) color, and on the third view I set light color (0.2 alpha).

You can set any color and get color with alpha by using the below code:

File activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools = "http://schemas.android.com/tools"
    android:layout_width = "match_parent"
    android:layout_height = "match_parent"
    android:gravity = "center"
    android:orientation = "vertical"
    tools:context = "com.example.temp.MainActivity" >

    <View
        android:id = "@+id/fullColorView"
        android:layout_width = "100dip"
        android:layout_height = "100dip" />

    <View
        android:id = "@+id/halfalphaColorView"
        android:layout_width = "100dip"
        android:layout_height = "100dip"
        android:layout_marginTop = "20dip" />

    <View
        android:id = "@+id/alphaColorView"
        android:layout_width = "100dip"
        android:layout_height = "100dip"
        android:layout_marginTop = "20dip" />

</LinearLayout>

File MainActivity.java

public class MainActivity extends Activity {

    private View fullColorView, halfalphaColorView, alphaColorView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fullColorView = (View)findViewById(R.id.fullColorView);
        halfalphaColorView = (View)findViewById(R.id.halfalphaColorView);
        alphaColorView = (View)findViewById(R.id.alphaColorView);

        fullColorView.setBackgroundColor(Color.BLUE);
        halfalphaColorView.setBackgroundColor(getColorWithAlpha(Color.BLUE, 0.5f));
        alphaColorView.setBackgroundColor(getColorWithAlpha(Color.BLUE, 0.2f));
    }


    private int getColorWithAlpha(int color, float ratio) {
        int newColor = 0;
        int alpha = Math.round(Color.alpha(color) * ratio);
        int r = Color.red(color);
        int g = Color.green(color);
        int b = Color.blue(color);
        newColor = Color.argb(alpha, r, g, b);
        return newColor;
    }
}

Kotlin version:

private fun getColorWithAlpha(color: Int, ratio: Float): Int {
  return Color.argb(Math.round(Color.alpha(color) * ratio), Color.red(color), Color.green(color), Color.blue(color))
}

Done

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宁负流年不负卿
3楼-- · 2019-01-01 08:01

We can make transparent in this way also.

White color code - FFFFFF

70% white - #B3FFFFFF.

100% — FF 95% — F2 90% — E6 85% — D9 80% — CC 75% — BF 70% — B3 65% — A6 60% — 99 55% — 8C 50% — 80 45% — 73 40% — 66 35% — 59 30% — 4D 25% — 40 20% — 33 15% — 26 10% — 1A 5% — 0D 0% — 00

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若你有天会懂
4楼-- · 2019-01-01 08:02

Make the color have 80% in the alpha channel. For example, for red use #CCFF0000:

<TextView
   ...
   android:background="#CCFF0000" />

In the example, CC is the hexadecimal number for 255 * 0.8 = 204. Note that the first two hexadecimal digits are for the alpha channel. The format is #AARRGGBB, where AA is the alpha channel, RR is the red channel, GG is the green channel and BB is the blue channel.

I'm assuming that 20% transparent means 80% opaque. If you meant the other way, instead of CC use 33 which is the hexadecimal for 255 * 0.2 = 51.

In order to calculate the proper value for an alpha transparency value you can follow this procedure:

  1. Given a transparency percentage, for example 20%, you know the opaque percentage value is 80% (this is 100-20=80)
  2. The range for the alpha channel is 8 bits (2^8=256), meaning the range goes from 0 to 255.
  3. Project the opaque percentage into the alpha range, that is, multiply the range (255) by the percentage. In this example 255 * 0.8 = 204. Round to the nearest integer if needed.
  4. Convert the value obtained in 3., which is in base 10, to hexadecimal (base 16). You can use Google for this or any calculator. Using Google, type "204 to hexa" and it will give you the hexadecimal value. In this case it is 0xCC.
  5. Prepend the value obtained in 4. to the desired color. For example, for red, which is FF0000, you will have CCFF0000.

You can take a look at the Android documentation for colors.

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长期被迫恋爱
5楼-- · 2019-01-01 08:08

You can try to do something like:

textView.getBackground().setAlpha(51);

Here you can set the opacity between 0 (fully transparent) to 255 (completely opaque). The 51 is exactly the 20% you want.

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零度萤火
6楼-- · 2019-01-01 08:10

Use a color with an alpha value like #33------, and set it as background of your editText using the XML attribute android:background=" ".

  1. 0% (transparent) -> #00 in hex
  2. 20% -> #33
  3. 50% -> #80
  4. 75% -> #C0
  5. 100% (opaque) -> #FF

255 * 0.2 = 51 → in hex 33

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人间绝色
7楼-- · 2019-01-01 08:11

In Android Studio there is a built-in tool to adjust the color and alpha/opacity value:

Android Adjust Color Opacity

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