FAB 根据列表的滚动而向上和向下移动

ScrollAwareFABBehavior.java

package com.github.keng42.jkisms.util;

import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.view.ViewCompat;
import android.support.v4.view.ViewPropertyAnimatorListener;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by Keng on 2015/9/13
 * FAB 根据列表的滚动而向上和向下移动
 */
public class ScrollAwareFABBehavior extends FloatingActionButton.Behavior {

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

    @Override
    public boolean onStartNestedScroll(
            CoordinatorLayout coordinatorLayout, FloatingActionButton child,
            View directTargetChild, View target, int nestedScrollAxes) {
        return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL ||
                super.onStartNestedScroll(coordinatorLayout, child,
                        directTargetChild, target, nestedScrollAxes);
    }

    // 收尾动画是否执行中
    private boolean mAnimating;
    // 按钮是否正在向上移动
    private boolean mFabMovingUp;

    @Override
    public void onStopNestedScroll(
            CoordinatorLayout coordinatorLayout,
            FloatingActionButton child, View target) {
        super.onStopNestedScroll(coordinatorLayout, child, target);

        // 当前动画结束后才能进行下一次动画
        ViewPropertyAnimatorListener listener = new ViewPropertyAnimatorListener() {
            @Override
            public void onAnimationStart(View view) {
                mAnimating = true;
            }

            @Override
            public void onAnimationEnd(View view) {
                mAnimating = false;
            }

            @Override
            public void onAnimationCancel(View view) {
                mAnimating = false;
            }
        };

        if (mFabMovingUp && !mAnimating) {
            // 按钮之前做上移动作，完成剩余移动
            ViewCompat.animate(child).translationY(0).withLayer().setListener(listener).start();
        }
        if (!mFabMovingUp && !mAnimating) {
            // 按钮之前做下移动作，完成剩余移动
            CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
            int fabBottomMargin = lp.bottomMargin;
            int distanceToScroll = child.getHeight() + fabBottomMargin;
            ViewCompat.animate(child).translationY(distanceToScroll).withLayer().setListener(listener).start();
        }
    }

    @Override
    public void onNestedScroll(
            CoordinatorLayout coordinatorLayout, FloatingActionButton child,
            View target, int dxConsumed, int dyConsumed, int dxUnconsumed,
            int dyUnconsumed) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed,
                dyConsumed, dxUnconsumed, dyUnconsumed);
        CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
        int fabBottomMargin = lp.bottomMargin;
        int distanceToScroll = child.getHeight() + fabBottomMargin;
        if (dyConsumed > 0) {
            // 手指向上划，按钮向下移动
            mFabMovingUp = false;
            if (child.getTranslationY() <= distanceToScroll) {
                child.setTranslationY(child.getTranslationY() + dyConsumed);
            }
        } else if (dyConsumed < 0) {
            mFabMovingUp = true;
            if (child.getTranslationY() >= 0) {
                child.setTranslationY(child.getTranslationY() + dyConsumed);
            }
        }
    }
}