android – Button with background color and transparent text-ThrowExceptions

Exception or error:

I have a layout with some background image and have a button on it. The background color of the button is, say, white. Now I want to write a text on it in such a way that the text displays anything that is behind the button through it (like transparent text). Now, obviously, if I make the text color transparent, the text will disappear and I will be seeing a white button with no text. How to do this?

Screenshot:

button with transparent text

How to solve:

Two ways: (1) not precise solution as text alignment should be coded by hands but:

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

    Button view1 = new Button(this);

    RelativeLayout layout1 = (RelativeLayout) findViewById(R.id.layout1);
    layout1.setBackground(getResources().getDrawable(R.drawable.choose_background));

    layout1.addView(view1);

    Bitmap mainImage = Bitmap.createBitmap(500, 500, Bitmap.Config.ARGB_8888);
    {
        //creating image is not necessary, more important is ability to grab the bitmap.
        Canvas canvas = new Canvas(mainImage);
        canvas.drawColor(Color.WHITE);
        view1.setBackground(new BitmapDrawable(getResources(), mainImage));
    }

    {
        Canvas canvas = new Canvas(mainImage);
        //most interesting part:
        Paint eraserPaint = new Paint();
        eraserPaint.setAlpha(0); //this
        eraserPaint.setTextSize(200);
        eraserPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN)); //and this
        canvas.drawText("some", 10, 150, eraserPaint);
    }
}

the idea of eraserPaint is from here Erase bitmap parts using PorterDuff mode and here Android how to apply mask on ImageView?

in activity_main.xml everything is default:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/layout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.runup.myapplication2.app.MainActivity">

and the result is:

enter image description here

(2) Second way is to add this behavior to class in order to use it in xml.
https://github.com/togramago/ClearTextViewProject – library project with a sample. You may add as a library or copy only ClearTextView class to your project (as it is an extended TextView without xml resources). works on configuration change and dynamical text and/or background changes.

The result of the sample in portrait: enter image description here

and in landscape: enter image description here

Leave a Reply

Your email address will not be published. Required fields are marked *