src/com/android/launcher3/views/SpringRelativeLayout.java

/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * 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.android.launcher3.views;

import android.content.Context;
import android.graphics.Canvas;
import android.support.animation.FloatPropertyCompat;
import android.support.animation.SpringAnimation;
import android.support.animation.SpringForce;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.RecyclerView.EdgeEffectFactory;
import android.util.AttributeSet;
import android.util.Log;
import android.util.SparseBooleanArray;
import android.view.View;
import android.widget.EdgeEffect;
import android.widget.RelativeLayout;

import static android.support.animation.SpringForce.DAMPING_RATIO_MEDIUM_BOUNCY;
import static android.support.animation.SpringForce.STIFFNESS_LOW;
import static android.support.animation.SpringForce.STIFFNESS_MEDIUM;

public class SpringRelativeLayout extends RelativeLayout {

    private static final float STIFFNESS = (STIFFNESS_MEDIUM + STIFFNESS_LOW) / 2;
    private static final float DAMPING_RATIO = DAMPING_RATIO_MEDIUM_BOUNCY;
    private static final float VELOCITY_MULTIPLIER = 0.3f;

    private static final FloatPropertyCompat<SpringRelativeLayout> DAMPED_SCROLL =
            new FloatPropertyCompat<SpringRelativeLayout>("value") {

                @Override
                public float getValue(SpringRelativeLayout object) {
                    return object.mDampedScrollShift;
                }

                @Override
                public void setValue(SpringRelativeLayout object, float value) {
                    object.setDampedScrollShift(value);
                }
            };

    private final SparseBooleanArray mSpringViews = new SparseBooleanArray();
    private final SpringAnimation mSpring;

    private float mDampedScrollShift = 0;

    public SpringRelativeLayout(Context context) {
        this(context, null);
    }

    public SpringRelativeLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SpringRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mSpring = new SpringAnimation(this, DAMPED_SCROLL, 0);
        mSpring.setSpring(new SpringForce(0)
                .setStiffness(STIFFNESS)
                .setDampingRatio(DAMPING_RATIO));
    }

    public void addSpringView(int id) {
        mSpringViews.put(id, true);
    }

    @Override
    protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
        if (mDampedScrollShift != 0 && mSpringViews.get(child.getId())) {
            canvas.translate(0, mDampedScrollShift);
            boolean result = super.drawChild(canvas, child, drawingTime);
            canvas.translate(0, -mDampedScrollShift);
            return result;
        }
        return super.drawChild(canvas, child, drawingTime);
    }

    private void setDampedScrollShift(float shift) {
        if (shift != mDampedScrollShift) {
            mDampedScrollShift = shift;
            invalidate();
        }
    }

    private void finishScrollWithVelocity(float velocity) {
        mSpring.setStartVelocity(velocity);
        mSpring.setStartValue(mDampedScrollShift);
        mSpring.start();
    }

    public EdgeEffectFactory createEdgeEffectFactory() {
        return new SpringEdgeEffectFactory();
    }

    private class SpringEdgeEffectFactory extends EdgeEffectFactory {

        @NonNull @Override
        protected EdgeEffect createEdgeEffect(RecyclerView view, int direction) {
            switch (direction) {
                case DIRECTION_TOP:
                    return new SpringEdgeEffect(getContext(), +VELOCITY_MULTIPLIER);
                case DIRECTION_BOTTOM:
                    return new SpringEdgeEffect(getContext(), -VELOCITY_MULTIPLIER);
            }
            return super.createEdgeEffect(view, direction);
        }
    }

    private class SpringEdgeEffect extends EdgeEffect {

        private final float mVelocityMultiplier;

        private float mDistance;

        public SpringEdgeEffect(Context context, float velocityMultiplier) {
            super(context);
            mVelocityMultiplier = velocityMultiplier;
        }

        @Override
        public boolean draw(Canvas canvas) {
            return false;
        }

        @Override
        public void onAbsorb(int velocity) {
            finishScrollWithVelocity(velocity * mVelocityMultiplier);
        }

        @Override
        public void onPull(float deltaDistance, float displacement) {
            mDistance += deltaDistance * (mVelocityMultiplier / 3f);
            setDampedScrollShift(mDistance * getHeight());
        }

        @Override
        public void onRelease() {
            mDistance = 0;
            finishScrollWithVelocity(0);
        }
    }
}