先来看一下效果：

scrollzoom_listview.gif

一、设计思路与实现步骤
1、本例是通过重写ListView来实现的，头部的图片是ListView的HeadView。定义一个headview.xml布局文件，在这个布局文件中放一个ImageView，并给IamgeView设置一个初始高度
2、实现下拉图片放大
当ListView处于顶部的时候下拉实现图片放大，这里要用的一个核心的方法是overScrollBy方法，当View的滑动超过了正常内容的边界时，该方法被调用。这里也许我解释的不是非常完美，大家可以自己去看一下该方法的注释

    /**
     * Scroll the view with standard behavior for scrolling beyond the normal
     * content boundaries. Views that call this method should override
     * {@link #onOverScrolled(int, int, boolean, boolean)} to respond to the
     * results of an over -scroll operation.
     *
     * Views can use this method to handle any touch or fling -based scrolling.
     *
     * @param deltaX Change in X in pixels
     * @param deltaY Change in Y in pixels
     * @param scrollX Current X scroll value in pixels before applying deltaX
     * @param scrollY Current Y scroll value in pixels before applying deltaY
     * @param scrollRangeX Maximum content scroll range along the X axis
     * @param scrollRangeY Maximum content scroll range along the Y axis
     * @param maxOverScrollX Number of pixels to overscroll by in either direction
     *          along the X axis.
     * @param maxOverScrollY Number of pixels to overscroll by in either direction
     *          along the Y axis.
     * @param isTouchEvent true if this scroll operation is the result of a touch event.
     * @return true if scrolling was clamped to an over-scroll boundary along either
     *          axis, false otherwise.
     */

deltaX表示X轴上过度滑动多出的那部分距离，deltaY表示Y轴上过度滑动多出的那部分距离。那么我们可以得出一个结论：图片的高度=图片原有的高度+|deltaY|，实际上无论是deltaY还是deltaX都是有正负之分的，当ListView处于顶部且的下拉的时候deltaY<0
当ListView处于底部的时候上拉deltaY>0。
3、实现上拉图片缩小恢复
这一步的核心方法是onScrollChanged，不断的监听图片的高度，并且重新绘制界面
图片的高度=图片原有高度-超出屏幕部分的高度
4、实现松手会弹动画
（1）自定义一个动画
（2）重写onTouchEvent方法UP事件的时候启动动画

二、具体实现
1、在重写ListView之前，我们先把准备工作做一下：
MaiinActivity

package lc.com.ui_zoomlistview;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ZoomListView zoomListView;
    private ImageView imageView;
    private List<String> list;
    private ItemAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initViews();
        initData();
    }

    private void initData() {
        // TODO Auto-generated method stub

        for (int i = 0; i < 20; i++) {
            list.add("测试数据" + i);
        }
        adapter.notifyDataSetChanged();
    }

    private void initViews() {
        // TODO Auto-generated method stub
        list = new ArrayList<String>();
        adapter = new ItemAdapter(list, this);
        zoomListView = (ZoomListView) findViewById(R.id.zoomListView);

        // 加载布局文件
        View header = View.inflate(MainActivity.this, R.layout.headview,
                null);

        imageView = (ImageView) header.findViewById(R.id.layout_header_image);
        // 将ImageView传递给ListView
        zoomListView.setImageView(imageView);
        // 给ListView添加头文件
        zoomListView.addHeaderView(header);
        // 设置适配器
        zoomListView.setAdapter(adapter);
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="lc.com.ui_zoomlistview.MainActivity">

    <lc.com.ui_zoomlistview.ZoomListView
        android:id="@+id/zoomListView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</RelativeLayout>

ItemAdapter

package lc.com.ui_zoomlistview;

import java.util.List;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

public class ItemAdapter extends BaseAdapter {

    private List<String> list;

    private Context mContext;

    private LayoutInflater mInflater;

    public ItemAdapter(List<String> list, Context mContext) {
        super();
        this.list = list;
        this.mContext = mContext;
        mInflater = LayoutInflater.from(mContext);
    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        ViewHolder mViewHoder = null;
        if (convertView == null) {
            mViewHoder = new ViewHolder();
            convertView = mInflater.inflate(R.layout.item, null);
            mViewHoder.item = (TextView) convertView.findViewById(R.id.item);
            convertView.setTag(mViewHoder);

        } else {
            mViewHoder = (ViewHolder) convertView.getTag();
        }
        mViewHoder.item.setText(getItem(position).toString());
        return convertView;
    }

    class ViewHolder {
        TextView item;
    }
}

item.xml

<?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:orientation="vertical" >

    <TextView
        android:id="@+id/item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="15dp" />

</LinearLayout>

很简单不做停留。下面我们开始真正的重头戏，ZoomListView的实现：

2、ZoomListView

package lc.com.ui_zoomlistview;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Transformation;
import android.widget.ImageView;
import android.widget.ListView;

/**
 * Created by HP on 2017/4/13.
 */

public class ZoomListView extends ListView {
    private static final String TAG = "ZoomListView";
    //ImageView的初始的高度
    private int mImageViewHeight;
    private ImageView mImageView;

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

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

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

    /**
     * 初始化一些必要的条件
     */
    private void init() {
        //获取mIageView的初始高度
        mImageViewHeight = getContext().getResources().getDimensionPixelSize(R.dimen.size_default_height);
        Log.e(TAG, "mImageViewHeight:" + mImageViewHeight);
    }

    /**
     * 设置ImageView
     *
     * @param imageView
     */
    public void setImageView(ImageView imageView) {
        this.mImageView = imageView;
    }

    /**
     * 步骤2：实现下拉图片大
     *
     * @param deltaY Y轴上超出的距离
     * @param deltaX X轴上超出的距离
     */
    @Override
    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent) {
        //当deltaY的时候表示向下过度滑动
        if (deltaY < 0) {
            Log.i(TAG, "deltaY:" + deltaY);
            int imageViewHeight = mImageView.getHeight() - deltaY;
            mImageView.getLayoutParams().height = imageViewHeight;
            //重新绘制ImageView
            mImageView.requestLayout();
        }
        //当deltaY>0的时候表示上拉过度
        else
        {
            if (mImageView.getHeight() > mImageViewHeight) {
                mImageView.getLayoutParams().height = mImageView.getHeight()
                        - deltaY;
                // 重新绘制，或者叫重新摆放
                mImageView.requestLayout();

            }
        }
        return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, maxOverScrollY, isTouchEvent);
    }

    /**
     * 步骤3：实现图片
     * *@param l
     * @param t
     * @param oldl
     * @param oldt
     */
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        //得到mImageView的父布局，这里明显是headview
        View parent = (View) mImageView.getParent();
        //实际内容的上边界到父布局上边界的距离
        int top = parent.getTop();
        if (top < 0 && mImageView.getHeight() > mImageViewHeight) {

            //计算图片的高度
            int imageViewHeight = mImageView.getHeight() + top;
            mImageView.getLayoutParams().height = imageViewHeight;
            //重新布局
            parent.layout(parent.getLeft(), 0, parent.getRight(), parent.getHeight());
            mImageView.requestLayout();
        }
        super.onScrollChanged(l, t, oldl, oldt);
    }

    /**
     * 步骤3：实现松手回弹动画
     *
     * @param ev
     * @return
     */
    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        //这里我们只需要实现UP事件
        if (ev.getAction() == MotionEvent.ACTION_UP) {
            Log.w(TAG, "UP");
            //情动回弹动画
            ResetAnimation animation = new ResetAnimation(mImageView);
            animation.setDuration(300);
            mImageView.startAnimation(animation);
        }
        return super.onTouchEvent(ev);
    }

    /**
     * 自定义一个会弹动画
     */
    class ResetAnimation extends Animation {


        private ImageView imageView;
        //高度差
        private int dHeight;

        //图片拉升以后的高度
        private int orginHeight;



        public ResetAnimation(ImageView imageView) {
            this.imageView = imageView;
            orginHeight=this.imageView.getHeight();
            dHeight = orginHeight - mImageViewHeight;
            Log.w(TAG, "dHeight：" + dHeight);
        }

        /**
         * 这个方法是为一个自定义动画需要重写的方法
         *
         * @param interpolatedTime 动画时间0~1.0
         * @param t
         */
        @Override
        protected void applyTransformation(float interpolatedTime, Transformation t) {
            Log.w(TAG, "applyTransformation");
            Log.w(TAG, "interpolatedTime：" + interpolatedTime);
            //设置图片的大小

            //计算图片的高度
            int imageViewHeight = (int) (orginHeight - dHeight * interpolatedTime);
            mImageView.getLayoutParams().height = imageViewHeight;
            mImageView.requestLayout();
            super.applyTransformation(interpolatedTime, t);
        }
    }
}