CoordinatorLayout与ListView协同让FAB悬浮按钮从底部消失及出现

CoordinatorLayout协同布局在一般只结合RecyclerView和NestedScrollView使用，如果我使用ListView没有效果的。但是，由于业务原因使用ListView，有需要实现协同的效果怎么办？

其实分析RecyclerView和NestedScrollView的源码可以知道，他们都实现了一个接口NestedScrollingChild，所以我们可以自定义ListView，实现NestedScrollingChild接口就好。当然除此外，google还提供了一个API
mListView.setNestedScrollingEnabled(true),就可以使用。当然，这2种方法只有在Android5.0以上才有效果。

下面就滑动ListView，让fab悬浮按钮滑动出现和滑动消失为例：

这里需要自定义一个Behavior类，这个类将作用于fab悬浮按钮，也就是在fab悬浮按钮中使用这个属性，如下：

app:layout_behavior="www.weshared.listviewandcoor.QuickReturnFooterBehavior"

具体代码如下：

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="www.weshared.listviewandcoor.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_main" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        app:layout_behavior="www.weshared.listviewandcoor.QuickReturnFooterBehavior"
        android:layout_margin="@dimen/fab_margin"
        android:src="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

content_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="www.weshared.listviewandcoor.MainActivity"
    tools:showIn="@layout/activity_main">

    <ListView
        android:id="@+id/lv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />
</RelativeLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="60dp">

    <TextView xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/tv_item"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:gravity="center"
        android:text="ee">
    </TextView>

</RelativeLayout>

MainActivity文件中

public class MainActivity extends AppCompatActivity {
    private ArrayList<String> mdatas = new ArrayList();
    private ListView mListView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        initView();

    }

    private void initView() {
        mListView = (ListView) findViewById(R.id.lv);
        //API21以上才有效果----第二种方式，比较简便
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            mListView.setNestedScrollingEnabled(true);
        }
        initData();
        mListView.setAdapter(new MyListAdapter(mdatas));
    }

    private void initData() {
        for(int i=0;i<30;i++){
            mdatas.add("---------"+i+"-----------");
        }
    }
}

MyListAdapter文件就省略吧

自定义ListView实现NestedScrollingChild接口,看代码也可以知道，其实发挥作用的就是setNestedScrollingEnabled(true)这个方法

public class NestedScrollingListView extends ListView implements NestedScrollingChild {
    private NestedScrollingChildHelper mNestedScrollingChildHelper;

    public NestedScrollingListView(final Context context) {
        super(context);
        initHelper();

    }

    public NestedScrollingListView(final Context context, final AttributeSet attrs) {
        super(context, attrs);
        initHelper();
    }

    public NestedScrollingListView(final Context context, final AttributeSet attrs, final int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initHelper();
    }

    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
    public NestedScrollingListView(final Context context, final AttributeSet attrs, final int defStyleAttr, final int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        initHelper();
    }

    private void initHelper() {
        mNestedScrollingChildHelper = new NestedScrollingChildHelper(this);
        setNestedScrollingEnabled(true);
    }

    @Override
    public void setNestedScrollingEnabled(final boolean enabled) {
        mNestedScrollingChildHelper.setNestedScrollingEnabled(enabled);
    }

    @Override
    public boolean isNestedScrollingEnabled() {
        return mNestedScrollingChildHelper.isNestedScrollingEnabled();
    }

    @Override
    public boolean startNestedScroll(final int axes) {
        return mNestedScrollingChildHelper.startNestedScroll(axes);
    }

    @Override
    public void stopNestedScroll() {
        mNestedScrollingChildHelper.stopNestedScroll();
    }

    @Override
    public boolean hasNestedScrollingParent() {
        return mNestedScrollingChildHelper.hasNestedScrollingParent();
    }

    @Override
    public boolean dispatchNestedScroll(final int dxConsumed, final int dyConsumed, final int dxUnconsumed, final int dyUnconsumed, final int[] offsetInWindow) {
        return mNestedScrollingChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedPreScroll(final int dx, final int dy, final int[] consumed, final int[] offsetInWindow) {
        return mNestedScrollingChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedFling(final float velocityX, final float velocityY, final boolean consumed) {
        return mNestedScrollingChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
    }

    @Override
    public boolean dispatchNestedPreFling(final float velocityX, final float velocityY) {
        return mNestedScrollingChildHelper.dispatchNestedPreFling(velocityX, velocityY);
    }
}

最重要的一个类Behavior的实现类

public class QuickReturnFooterBehavior extends CoordinatorLayout.Behavior<View> {
    private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();

    private int mDySinceDirectionChange;
    private boolean mIsShowing;
    private boolean mIsHiding;

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

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) {
        return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx, int dy, int[] consumed) {
        if (dy > 0 && mDySinceDirectionChange < 0
                || dy < 0 && mDySinceDirectionChange > 0) {
            // We detected a direction change- cancel existing animations and reset our cumulative delta Y
            child.animate().cancel();
            mDySinceDirectionChange = 0;
        }

        mDySinceDirectionChange += dy;

        if (mDySinceDirectionChange > child.getHeight()
                && child.getVisibility() == View.VISIBLE
                && !mIsHiding) {
            hide(child);
        } else if (mDySinceDirectionChange < 0
                && child.getVisibility() == View.GONE
                && !mIsShowing) {
            show(child);
        }
    }

    /**
     * Hide the quick return view.
     *
     * Animates hiding the view, with the view sliding down and out of the screen.
     * After the view has disappeared, its visibility will change to GONE.
     *
     * @param view The quick return view
     */
    private void hide(final View view) {
        mIsHiding = true;
        ViewPropertyAnimator animator = view.animate()
                .translationY(view.getHeight())
                .setInterpolator(INTERPOLATOR)
                .setDuration(200);

        animator.setListener(new Animator.AnimatorListener() {
            @Override
            public void onAnimationStart(Animator animator) {}

            @Override
            public void onAnimationEnd(Animator animator) {
                // Prevent drawing the View after it is gone
                mIsHiding = false;
                view.setVisibility(View.GONE);
            }

            @Override
            public void onAnimationCancel(Animator animator) {
                // Canceling a hide should show the view
                mIsHiding = false;
                if (!mIsShowing) {
                    show(view);
                }
            }

            @Override
            public void onAnimationRepeat(Animator animator) {}
        });

        animator.start();
    }

    /**
     * Show the quick return view.
     *
     * Animates showing the view, with the view sliding up from the bottom of the screen.
     * After the view has reappeared, its visibility will change to VISIBLE.
     *
     * @param view The quick return view
     */
    private void show(final View view) {
        mIsShowing = true;
        ViewPropertyAnimator animator = view.animate()
                .translationY(0)
                .setInterpolator(INTERPOLATOR)
                .setDuration(200);

        animator.setListener(new Animator.AnimatorListener() {
            @Override
            public void onAnimationStart(Animator animator) {
                view.setVisibility(View.VISIBLE);
            }

            @Override
            public void onAnimationEnd(Animator animator) {
                mIsShowing = false;
            }

            @Override
            public void onAnimationCancel(Animator animator) {
                // Canceling a show should hide the view
                mIsShowing = false;
                if (!mIsHiding) {
                    hide(view);
                }
            }

            @Override
            public void onAnimationRepeat(Animator animator) {}
        });

        animator.start();
    }
}