Material Design の FloatingActionButton のためのクラスを作ってみた

activity_main.xml

<!-- 使い方はこんな感じ -->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin">

    <com.uphyca.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="56dp"
        android:layout_height="56dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:src="@drawable/ic_action_new"/>

</RelativeLayout>

FloatingActionButton.java

/*
 * Copyright (C) 2014 uPhyca Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.uphyca.widget;

import android.animation.Animator;
import android.animation.ObjectAnimator;
import android.animation.StateListAnimator;
import android.content.Context;
import android.content.res.ColorStateList;
import android.content.res.Resources;
import android.graphics.Outline;
import android.graphics.drawable.GradientDrawable;
import android.graphics.drawable.RippleDrawable;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.TypedValue;
import android.widget.ImageButton;

/**
 * FloatingActionButton のための UI パーツです。
 *
 * 以下の様な感じで使います。
 * <pre>
 * &lt;com.uphyca.widget.FloatingActionButton
 *     android:id="@+id/fab"
 *     android:layout_width="56dp"
 *     android:layout_height="56dp"
 *     android:src="@drawable/ic_action_new"/&gt;
 * </pre>
 */
public class FloatingActionButton extends ImageButton {

    private static final int DEFAULT_ELEVATION_IN_DP = 2;
    private static final int DEFAULT_PRESSED_ELEVATION_IN_DP = 4;

    public FloatingActionButton(Context context) {
        super(context);
        init(context);
    }

    public FloatingActionButton(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public FloatingActionButton(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context);
    }

    public FloatingActionButton(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init(context);
    }

    private void init(Context context) {
        final DisplayMetrics dm = context.getResources().getDisplayMetrics();
        final float scale = dm.density;

        final int elevation = (int) (DEFAULT_ELEVATION_IN_DP * scale + .5f);
        final int pressedElevation = (int) (DEFAULT_PRESSED_ELEVATION_IN_DP * scale + .5f);
        final long duration = context.getResources().getInteger(android.R.integer.config_shortAnimTime);

        setElevation(elevation);
        initElevationAnimator(elevation, pressedElevation, duration);

        final int colorAccentValue;
        final int colorControlHighlightValue;
        if (isInEditMode()) {
            colorAccentValue = 0xff03a9f4;
            colorControlHighlightValue = 0x20444444;
        } else {
            final Resources.Theme theme = context.getTheme();

            final TypedValue outValue = new TypedValue();
            theme.resolveAttribute(android.R.attr.colorAccent, outValue, true);
            colorAccentValue = outValue.data;

            theme.resolveAttribute(android.R.attr.colorControlHighlight, outValue, true);
            colorControlHighlightValue = outValue.data;
        }

        final GradientDrawable ovalBackground = new GradientDrawable();
        ovalBackground.setShape(GradientDrawable.OVAL);
        ovalBackground.setColor(colorAccentValue);

        final RippleDrawable rippleDrawable = new RippleDrawable(ovalBackground, ovalBackground);
        final ColorStateList rippleColors = new ColorStateList(new int[][]{EMPTY_STATE_SET}, new int[]{colorControlHighlightValue});
        rippleDrawable.setColor(rippleColors);

        setBackground(rippleDrawable);
    }

    private void initElevationAnimator(float elevation, float pressedElevation, long duration) {
        final Animator onPressedAnimator = ObjectAnimator.ofFloat(this, "translationZ",
                elevation, pressedElevation);
        onPressedAnimator.setStartDelay(0L);
        onPressedAnimator.setDuration(duration);
        final Animator defaultAnimator = ObjectAnimator.ofFloat(this, "translationZ",
                pressedElevation, elevation);
        defaultAnimator.setStartDelay(0L);
        defaultAnimator.setDuration(duration);

        final StateListAnimator slm = new StateListAnimator();
        slm.addState(PRESSED_ENABLED_STATE_SET, onPressedAnimator);
        slm.addState(EMPTY_STATE_SET, defaultAnimator);

        setStateListAnimator(slm);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        final Outline outline = new Outline();
        outline.setOval(0, 0, w, h);

        setOutline(outline);
    }
}