Эффект слайда вниз на ExpandableListView

Изменить: пошаговое руководство:

Сначала я создаю xml list_row:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/row_parent"
    android:orientation="vertical">
    <RelativeLayout 
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/row_simple_parent"
        >
    <View
        android:id="@+id/row_simple_parent_invis_cover"
        android:visibility="gone"
        android:layout_height="something that fills out your content"
        android:layout_width="match_parent"
        android:background="@android:color/transparent"/>
    </RelativeLayout>

    <!-- Dropdown -->
    <RelativeLayout 
        android:id="@+id/row_dropdown"
        android:layout_height="wrap_content"
        android:layout_width="match_parent">
    </RelativeLayout>
</LinearLayout>

Анимация раскрывающегося списка следующая:

import android.app.Activity;
import android.util.DisplayMetrics;
import android.view.View;
import android.view.View.MeasureSpec;
import android.view.animation.Animation;
import android.view.animation.Transformation;

/**
 * Class for handling collapse and expand animations.
 * @author Esben Gaarsmand
 *
 */
public class ExpandCollapseAnimation extends Animation {
    private View mAnimatedView;
    private int mEndHeight;
    private int mStartVisibility;

    /**
     * Initializes expand collapse animation. If the passed view is invisible/gone the animation will be a drop down, 
     * if it is visible the animation will be collapse from bottom
     * @param view The view to animate
     * @param duration
     */ 
    public ExpandCollapseAnimation(View view, int duration) {
        setDuration(duration);
        mAnimatedView = view;
        mEndHeight = mAnimatedView.getLayoutParams().height;
        mStartVisibility = mAnimatedView.getVisibility();
        if(mStartVisibility == View.GONE || mStartVisibility == View.INVISIBLE) {
            mAnimatedView.setVisibility(View.VISIBLE);
            mAnimatedView.getLayoutParams().height = 0;
        }
    }

    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
        super.applyTransformation(interpolatedTime, t);
        if (interpolatedTime < 1.0f) {
            if(mStartVisibility == View.GONE || mStartVisibility == View.INVISIBLE) {
                mAnimatedView.getLayoutParams().height = (int) (mEndHeight * interpolatedTime);
            } else {
                mAnimatedView.getLayoutParams().height = mEndHeight - (int) (mEndHeight * interpolatedTime);
            }
            mAnimatedView.requestLayout();
        } else {
            if(mStartVisibility == View.GONE || mStartVisibility == View.INVISIBLE) {
                mAnimatedView.getLayoutParams().height = mEndHeight;
                mAnimatedView.requestLayout();
            } else {
                mAnimatedView.getLayoutParams().height = 0;
                mAnimatedView.setVisibility(View.GONE);
                mAnimatedView.requestLayout();
                mAnimatedView.getLayoutParams().height = mEndHeight;
            }
        }
    }

    /**
     * This methode can be used to calculate the height and set itm for views with wrap_content as height. 
     * This should be done before ExpandCollapseAnimation is created.
     * @param activity
     * @param view
     */
    public static void setHeightForWrapContent(Activity activity, View view) {
        DisplayMetrics metrics = new DisplayMetrics();
        activity.getWindowManager().getDefaultDisplay().getMetrics(metrics);

        int screenWidth = metrics.widthPixels;

        int heightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
        int widthMeasureSpec = MeasureSpec.makeMeasureSpec(screenWidth, MeasureSpec.EXACTLY);

        view.measure(widthMeasureSpec, heightMeasureSpec);
        int height = view.getMeasuredHeight();
        view.getLayoutParams().height = height;
    }
}

Затем внутри моего адаптера (вы, конечно, добавите больше синтаксиса, и если вы хотите, чтобы выпадающий список не закрывался, когда его не видно в списке, вам нужно запомнить это в держателе с каким-то параметром):

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    final ViewHolder holder;
    if(convertView == null) {
        // setup holder
        holder = new ViewHolder();
        convertView = mInflater.inflate(R.layout.list_row, null);
        holder.mDropDown = convertView.findViewById(R.id.row_dropdown);
        convertView.setTag(holder);
    } else {
        // get existing row view
        holder = (ViewHolder) convertView.getTag();
    }
    holder.mDropDown.setVisibility(View.GONE);
    return convertView;
}

Затем в ваших списках onItemClick происходит волшебство:

@Override
public void onListItemClick(ListView list, View view, int position, long id) {
    final ListItem item = (ListItem) list.getAdapter().getItem(position);
    // set dropdown data
    ViewHolder holder = (ViewHolder) view.getTag();
    final View dropDown = holder.mDropDown;

    // set click close on top part of view, this is so you can click the view
    // and it can close or whatever, if you start to add buttons etc. you'll loose
    // the ability to click the view until you set the dropdown view to gone again.
    final View simpleView = view.findViewById(R.id.row_simple_parent_invis_cover);
    simpleView.setVisibility(View.VISIBLE);

    final Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            if(msg.what == 0) {
                // first we measure height, we need to do this because we used wrap_content
                // if we use a fixed height we could just pass that in px.
                ExpandCollapseAnimation.setHeightForWrapContent(getActivity(), dropDown);
                ExpandCollapseAnimation expandAni = new ExpandCollapseAnimation(dropDown, DROP_DOWN_TIME);
                dropDown.startAnimation(expandAni);

                Message newMsg = new Message();

            } else if(msg.what == 1) {
                ExpandCollapseAnimation expandAni = new ExpandCollapseAnimation(dropDown, DROP_DOWN_TIME);
                dropDown.startAnimation(expandAni);

                simpleView.setOnClickListener(null);
                simpleView.setVisibility(View.GONE);
            }
        }
    };

    simpleView.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            handler.sendEmptyMessage(1);
        }
    });

    // start drop down animation
    handler.sendEmptyMessage(0);
}

Заключительный комментарий: я не уверен, что это лучший способ сделать это, но это сработало для меня.