How to create an overlay that blocks touch events to UI below it?

Following code will add overlay on top of everything :

View v1 = new View(this);    
WindowManager.LayoutParams params = new WindowManager.LayoutParams(
 1000,
 50,
 WindowManager.LayoutParams.TYPE_SYSTEM_ALERT,
 WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE |
 WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN,
 PixelFormat.OPAQUE);

params.gravity = Gravity.BOTTOM;
WindowManager wm = (WindowManager) this.getSystemService(Context.WINDOW_SERVICE);
wm.addView(v1, params);

to block the touch event either you have to change the flag or below code will work:

protected boolean onTouchEvent (MotionEvent me) {
    return true;
}

For v1 you would do an import:

import android.view.View.OnTouchListener;

Then set the onTouchListener:

v1.setOnTouchListener(new OnTouchListener() {
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        return true;
    }
})

Below code has worked for me. I've added android:clickable="true" to block touch events to other views below it.

This is an example with a ProgressBar inside the overlay. If you don't want the ProgressBar, you can use the FrameLayout without it.

<FrameLayout
            xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/progress_overlay"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:alpha="0.4"
            android:animateLayoutChanges="true"
            android:background="@android:color/black"
            android:visibility="gone"
            android:clickable="true">

            <ProgressBar
                style="?android:attr/progressBarStyleLarge"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                android:indeterminate="true"/>

</FrameLayout>

If overlay doesn't get touch events, then the events are passed to underlying view, so to block touch events in views below it, make your overlay touchable. android:clickable="true"