Android Layout background alpha

Question

Hi I have a layout which I'm using to fill my page and I have to set a background image held in my drawable folder in that layout.

I want to then set the alpha value of the image to something quite low almost make the image like a water mark.

my xml looks like

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/background" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:background="@drawable/main_background" > 

As you can see I have assigned an id to the layout

I thought in my oncreate I could do something like this?

View backgroundimage = (View) findViewById(R.id.background); backgroundimage.setAlpha(80); 

This is not working however I suspect its because I'm trying to cast the background as a View what should I cast it as?

Answer 1

Try to use:

Drawable.setAlpha(); 

You should do something like this:

View backgroundImage = findViewById(R.id.background); Drawable background = backgroundImage.getBackground(); background.setAlpha(80); 

Answer 2

If you want to set alpha in xml then u can try this:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/background" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:background="#CC000000" > 

first 2 digits are used to set alpha here alpha is 80% next 6 digits for color code

Hence, alpha is set in hexadecimal coding. FF = 100% and 00 = 0%, thus 80% is not 80 in hexadecimal, for more standard values see this post.