FloatingActionButton.java

package  your_package;

import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.OvershootInterpolator;
import android.widget.FrameLayout;

@SuppressLint("ClickableViewAccessibility")
/**
 * Class for implement float action button in android apps from API 14
 * @author Roberto de Castro Rodríguez
 * @version 1.1
 * @since 02/12/2014
 */
public class FloatingActionButton extends View {

	final static OvershootInterpolator overshootInterpolator = new OvershootInterpolator();
	final static AccelerateInterpolator accelerateInterpolator = new AccelerateInterpolator();

	@SuppressWarnings("unused")
	private Context context;
	private Paint mButtonPaint;
	private Paint mDrawablePaint;
	private Bitmap mBitmap;
	private boolean mHidden = false;

	public FloatingActionButton(Context context) {
		super(context);
		this.context = context;
		init(Color.WHITE);
	}

	public void setFloatingActionButtonColor(int FloatingActionButtonColor) {
		init(FloatingActionButtonColor);
	}

	public void setFloatingActionButtonDrawable(Drawable FloatingActionButtonDrawable) {
		mBitmap = ((BitmapDrawable) FloatingActionButtonDrawable).getBitmap();
		invalidate();
	}

	public void init(int FloatingActionButtonColor) {
		setWillNotDraw(false);
		setLayerType(View.LAYER_TYPE_SOFTWARE, null);

		mButtonPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mButtonPaint.setColor(FloatingActionButtonColor);
		mButtonPaint.setStyle(Paint.Style.FILL);
		mButtonPaint.setShadowLayer(10.0f, 0.0f, 3.5f, Color.argb(100, 0, 0, 0));
		mDrawablePaint = new Paint(Paint.ANTI_ALIAS_FLAG);

		invalidate();
	}

	@Override
	protected void onDraw(Canvas canvas) {
		setClickable(true);
		canvas.drawCircle(getWidth() / 2, getHeight() / 2, (float) (getWidth() / 2.6), mButtonPaint);
		canvas.drawBitmap(mBitmap, (getWidth() - mBitmap.getWidth()) / 2,
				(getHeight() - mBitmap.getHeight()) / 2, mDrawablePaint);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		if (event.getAction() == MotionEvent.ACTION_UP) {
			setAlpha(1.0f);
		} else if (event.getAction() == MotionEvent.ACTION_DOWN) {
			setAlpha(0.6f);
		}
		return super.onTouchEvent(event);
	}

	public void hideFloatingActionButton() {
		if (!mHidden) {
			ObjectAnimator scaleX = ObjectAnimator.ofFloat(this, "scaleX", 1, 0);
			ObjectAnimator scaleY = ObjectAnimator.ofFloat(this, "scaleY", 1, 0);
			AnimatorSet animSetXY = new AnimatorSet();
			animSetXY.playTogether(scaleX, scaleY);
			animSetXY.setInterpolator(accelerateInterpolator);
			animSetXY.setDuration(100);
			animSetXY.start();
			mHidden = true;
		}
	}

	public void showFloatingActionButton() {
		if (mHidden) {
			ObjectAnimator scaleX = ObjectAnimator.ofFloat(this, "scaleX", 0, 1);
			ObjectAnimator scaleY = ObjectAnimator.ofFloat(this, "scaleY", 0, 1);
			AnimatorSet animSetXY = new AnimatorSet();
			animSetXY.playTogether(scaleX, scaleY);
			animSetXY.setInterpolator(overshootInterpolator);
			animSetXY.setDuration(200);
			animSetXY.start();
			mHidden = false;
		}
	}

	public boolean isHidden() {
		return mHidden;
	}

	/**
	 * Class for build fab button from code
	 * @author Roberto de Castro Rodríguez
	 * @version 1.0
	 * @since 02/12/2014
	 */
	static public class Builder {
		/**
		 * Params of layout
		 */
		private FrameLayout.LayoutParams params;
		/**
		 * Activity of app
		 */
		private final Activity activity;
		/**
		 * Container where button is added
		 */
		private final ViewGroup container;
		/**
		 * Default gravity
		 */
		int gravity = Gravity.BOTTOM | Gravity.RIGHT; 
		/**
		 * Button's icon
		 */
		private Drawable drawable;
		/**
		 * Button's color
		 */
		int color = Color.WHITE;
		/**
		 * Button's size
		 */
		int size = 0;
		/**
		 * Button's scale
		 */
		float scale = 0;

		/**
		 * Builder of the fab button
		 * @param context activity for add the button
		 * @param container layout where add the button
		 */
		public Builder(Activity context, ViewGroup container) {
			scale = context.getResources().getDisplayMetrics().density;
			size = convertToPixels(72, scale); // default size is 72dp by 72dp
			params = new FrameLayout.LayoutParams(size, size);
			params.gravity = gravity;

			this.activity = context;
			this.container = container;
		}

		/**
		 * Sets the gravity for the FAB
		 */
		public Builder withGravity(int gravity) {
			this.gravity = gravity;
			return this;
		}

		/**
		 * Sets the margins for the FAB in dp
		 */
		public Builder withMargins(int left, int top, int right, int bottom) {
			params.setMargins(
					convertToPixels(left, scale),
					convertToPixels(top, scale),
					convertToPixels(right, scale),
					convertToPixels(bottom, scale));
			return this;
		}

		/**
		 * Sets the FAB drawable
		 */
		public Builder withDrawable(final Drawable drawable) {
			this.drawable = drawable;
			return this;
		}

		/**
		 * Sets the FAB color
		 */
		public Builder withButtonColor(final int color) {
			this.color = color;
			return this;
		}

		/**
		 * Sets the FAB size in dp
		 */
		public Builder withButtonSize(int size) {
			size = convertToPixels(size, scale);
			params = new FrameLayout.LayoutParams(size, size);
			return this;
		}

		/**
		 * Creation of the button
		 * @return fab button
		 */
		public FloatingActionButton create() {
			final FloatingActionButton button = new FloatingActionButton(activity);
			button.setFloatingActionButtonColor(this.color);
			button.setFloatingActionButtonDrawable(this.drawable);
			params.gravity = this.gravity;
			//ViewGroup root = (ViewGroup) activity.findViewById(android.R.id.content);
			
			this.container.addView(button, params);
			return button;
		}

		// The calculation (value * scale + 0.5f) is a widely used to convert to dps to pixel units
		// based on density scale
		// see developer.android.com (Supporting Multiple Screen Sizes)
		private int convertToPixels(int dp, float scale){
			return (int) (dp * scale + 0.5f) ;
		}
	}
}

HowToAdd.java

FloatingActionButton fab = new FloatingActionButton.Builder(this.getActivity(), (FrameLayout)rootView.findViewById(R.id.your_layout))
		.withDrawable(getResources().getDrawable(R.drawable.add_icon_activity))
		.withButtonColor(getResources().getColor(R.color.fab_color))
		.withGravity(Gravity.BOTTOM | Gravity.RIGHT)
		.withMargins(0, 0, 5, 5)
		.create();

If you want to put it on border of two layouts drawn one above another one can use this class as 👎

final RelativeLayout topLayout = (RelativeLayout) view
.findViewById(R.id.top_view);

        final ViewTreeObserver observer = topLayout.getViewTreeObserver();
        observer.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                topLayout.getHeight();

                fabButton = new FloatingActionButton.Builder(getActivity())
                        .withDrawable(
                                getResources().getDrawable(R.drawable.fab_icon))
                        .withButtonColor(Color.WHITE)
                        .withGravity(Gravity.TOP | Gravity.RIGHT)
                        .withMargins(0, topLayout.getHeight() - 72 + 30, 16, 0)
                        .create();

                fabButton.setOnClickListener(new OnClickListener() {

                    @Override
                    public void onClick(View arg0) {

                        fabButton.hideFloatingActionButton();

                        //DO something
                    }
                });

                topLayout.getViewTreeObserver().removeGlobalOnLayoutListener(
                        this);
            }
        });                                  Where in magic number- 72 + 30 , 72 is default width of fab icon  and 30 is bottomMargin given to top layout.

Out put will be like :-

|--------------------------------- |
|_TOP LAYOUT|
| (Fab) |
| |
|_BOTTOM LAYOUT |

We are looking to implement this button in our app on top of an expandable list view, but the button is behind the list, any thoughts?