Android and setting alpha for (image) view alpha

Question

Is there really no XML attribute counterpart to setAlpha(int)?

If not, what alternatives are there?

Answer 1

No, there is not, see how the "Related XML Attributes" section is missing in the ImageView.setAlpha(int) documentation. The alternative is to use View.setAlpha(float) whose XML counterpart is android:alpha. It takes a range of 0.0 to 1.0 instead of 0 to 255. Use it e.g. like

<ImageView android:alpha="0.4">

However, the latter in available only since API level 11.

Answer 2

Maybe a helpful alternative for a plain-colored background:

Put a LinearLayout over the ImageView and use the LinearLayout as a opacity filter. In the following a small example with a black background:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#FF000000" >

<RelativeLayout
    android:id="@+id/relativeLayout2"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/icon_stop_big" />

    <LinearLayout
        android:id="@+id/opacityFilter"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="#CC000000"
        android:orientation="vertical" >
    </LinearLayout>
</RelativeLayout>

Vary the android:background attribute of the LinearLayout between #00000000 (fully transparent) and #FF000000 (fully opaque).

Answer 3

The alpha can be set along with the color using the following hex format #ARGB or #AARRGGBB. See http://developer.android.com/guide/topics/resources/color-list-resource.html

Answer 4

I am not sure about the XML but you can do it by code in the following way.

ImageView myImageView = new ImageView(this);
myImageView.setAlpha(xxx);

In pre-API 11:

• range is from 0 to 255 (inclusive), 0 being transparent and 255 being opaque.

In API 11+:

• range is from 0f to 1f (inclusive), 0f being transparent and 1f being opaque.

Answer 5

It's easier than the other response. There is an xml value alpha that takes double values.

android:alpha="0.0" thats invisible

android:alpha="0.5" see-through

android:alpha="1.0" full visible

That's how it works.

Answer 6

setAlpha(int) is deprecated as of API 16: Android 4.1

Please use setImageAlpha(int) instead