ListView实现类似WheelView效果的探究

不得不说，作为一名安卓码农，总是会有蛋蛋的忧伤，因为CP常说的就是：你看，人家ios的那个效果好炫酷，比如下面这样的

作为一名合格的码农，实在不能忍，最后还是实现了这个效果，虽然没有ios的厉害。。。

实现的思路还是不复杂的，主要分两个方向：WheelView类似的思想（github一大堆）、ClipToPadding和ClipChildren取巧。因为我是用的取巧，所以我们下面只谈第二种方法。

难点有两个，一是精确地控制listview的item滚动到悬浮框内。因为大多数时候都不会是某个item刚好在悬浮框内的，但是唯一要考虑的情况也只有一种，即悬浮框内同时出现2个或多个item（设计需要，item的高度都是大于等于悬浮框的高度的，所以悬浮框内最多同时出现2个item，小于悬浮框的高度就会出现问题），取出最适合停留的item（这是个相对概念，大家可以修改代码扩展），我目前需要的就是item中间位置的y值和悬浮视图中间位置的y值最接近的一项，后面的代码里大家会看到如何处理的；

二是当listview只有很少的项时，怎么让listview可以滚动呢？这就需要ClipToPadding和ClipChildren来帮忙了。不知道这两个属性的童鞋可以上网查一查，我相信你会受益良多。ClipToPadding=false，我对这个属性简单理解就是，当你为listview设置了padingTop、padingBottom属性，listview会有pading的效果，但是当你滑动listview到顶部或底部时，listview的顶部或底部却不会出现pading的那部分区域，即listview的内容不再被pading的区域遮盖。ClipChildren=false，就是子视图可以超出父视图区域进行绘制。有了这两个属性，就可以解决listview item比较少时不能滚动的问题了。

由于设计需要滚动时item视图的放大和缩小，所以把处理放到了onscrolllistener的onscroll方法里，最后处理listview精确滚动的代码则要放到onscrolllistener的onScrollStateChanged方法里，这些都是可以修改的。

因为要实现这个效果需要adapter配合，所以代码也比较乱，但是注释还是比较详细的，大家慢慢看。

先看看WheelListView

package com.ykbjson.demo.customview.listview;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.AbsListView;
import android.widget.ListView;

import com.ykbjson.demo.tools.SLog;

/**
 * 包名：com.ykbjson.demo.customview.listview
 * 描述：类似WheelView的ListView
 * 创建者：yankebin
 * 日期：2016/6/1
 */
public class WheelListView extends ListView {
    private static final int MAX_Y_OVERSCROLL_DISTANCE = 200;
    private final Object SCROLL_LOCK = new Object();
    //坐标都是相对于手机屏幕
    private int topY;//悬浮框顶部坐标
    private int middleY;//悬浮框中间坐标
    private int bottomY;//悬浮框底部坐标
    private int selectPosition;//滚动时adapter当前选中的position
    private boolean fromTouch;//当调用smoothScrollToPositionFromTop()方法时也会触发onScroll，需要屏蔽掉
    private WheelAdapter wheelAdapter;//数据适配器
    private OnSelectCallback callback;//滚动时的回调接口
    private int mMaxYOverScrollDistance;

    public interface OnSelectCallback {
        void onHandleScroll(int selectPosition);

        void onHandleIdle(WheelListView wheelListView, int selectPosition);
    }

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

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

    public WheelListView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
//        initBounceListView();
        setClipChildren(false);
        setClipToPadding(false);
    }

    /**
     * 阻尼效果实现
     */
//    private void initBounceListView(){
//        //get the density of the screen and do some maths with it on the max overscroll distance
//        //variable so that you get similar behaviors no matter what the screen size
//        final DisplayMetrics metrics = getContext().getResources().getDisplayMetrics();
//        final float density = metrics.density;
//        mMaxYOverScrollDistance = (int) (density * MAX_Y_OVERSCROLL_DISTANCE);
//    }
//
//    @Override
//    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent){
//        //This is where the magic happens, we have replaced the incoming maxOverScrollY with our own custom variable mMaxYOverScrollDistance;
//        return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxYOverScrollDistance, isTouchEvent);
//    }

    public void setAdapter(WheelAdapter adapter) {
        super.setAdapter(adapter);
        wheelAdapter = adapter;
        setCallback(adapter);
    }

    private void setCallback(OnSelectCallback callback) {
        this.callback = callback;
    }

    /**
     * 初始化
     *
     * @param selectView
     * @param rootView
     */
    protected void setUp(View selectView, View rootView) {
        if (null == selectView || null == rootView) {
            return;
        }
        //让listview现实的区域刚好和悬浮框重合
        setPadding(0, selectView.getTop() , 0, rootView.getBottom() - selectView.getBottom() );

        int location1[] = new int[2];
        selectView.getLocationOnScreen(location1);

        topY = location1[1];
        middleY = topY + selectView.getMeasuredHeight() / 2;
        bottomY = topY + selectView.getMeasuredHeight();

        setUpScroll();
    }

    /**
     * 设置滚动监听
     */
    private void setUpScroll() {
        setOnScrollListener(new AbsListView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(AbsListView view, int scrollState) {
                if (null == callback) {
                    return;
                }
                if (scrollState == SCROLL_STATE_IDLE) {
                    if (!fromTouch) {
                        return;
                    }
                    fromTouch = false;
                    SLog.d("SCROLL_STATE_IDLE");
                    //adapter实现了callback接口
                    callback.onHandleIdle(WheelListView.this,selectPosition);
                } else if (scrollState == SCROLL_STATE_TOUCH_SCROLL) {
                    fromTouch = true;
                }
            }

            @Override
            public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
                if (null == callback) {
                    return;
                }
                if (!fromTouch) {
                    return;
                }
                synchronized (SCROLL_LOCK) {
                    handleScroll(firstVisibleItem);
                }
            }
        });
    }

    /**
     * 处理滚动
     *
     * @param firstVisibleItem
     */
    private void handleScroll(int firstVisibleItem) {
        //取出与中线距离最近的item
        int tempD = -1;
        //本次滑动计算出的position
        int tempP = -1;
        //遍历listview当前可见的item，不是所有item
        for (int i = 0; i < getChildCount(); i++) {
            //计算每个item相对于屏幕的坐标值
            View child = getChildAt(i);
            int location2[] = new int[2];
            child.getLocationOnScreen(location2);
            int childBottom = location2[1] + child.getMeasuredHeight();
            int childTop = location2[1];
            //            SLog.d("bottomY : " + bottomY + " topY : " + topY + " middleY : " + middleY + " childBottom : " + childBottom + " childTop : " + childTop);
            //在悬浮框区域外的，排除掉
            if (childBottom < topY || childTop > bottomY) {
                continue;
            }
            //找到item中线离悬浮框中线最近的item，比距离即可
            int childMiddleY = childBottom - child.getMeasuredHeight() / 2;
            int position = firstVisibleItem + i;//当前item真正的position
            int distance = Math.abs(middleY - childMiddleY);
            if (tempD == -1) {
                tempD = distance;
                tempP = position;
            } else if (tempD > distance) {
                tempD = distance;
                tempP = position;
            }
        }

        if (tempP < 0) {
            tempP = 0;
        } else if (tempP > wheelAdapter.getCount() - 1) {
            tempP = wheelAdapter.getCount() - 1;
        }
        //防止多次notify同一个position
        if (selectPosition == tempP) {
            return;
        }
        selectPosition = tempP;
        callback.onHandleScroll(selectPosition);
    }
}

再看看WheelAdapter

package com.ykbjson.demo.customview.listview;

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

import com.drivingassisstantHouse.library.base.SimpleAdapterHolder;

import java.util.List;

/**
 * 包名：com.ykbjson.demo.customview.listview
 * 描述：类似WheelView的ListView的adapter
 * 创建者：yankebin
 * 日期：2016/6/1
 */
public abstract class WheelAdapter<T> extends BaseAdapter implements WheelListView.OnSelectCallback {

    /**
     * 数据源
     */
    private List<T> mData;
    /**
     * 上下文
     */
    private Context mContext;
    /**
     * item布局索引
     */
    private int layoutId;


    public Context getmContext() {
        return mContext;
    }

    public void setmContext(Context mContext) {
        this.mContext = mContext;
    }

    public List<T> getmData() {
        return mData;
    }

    public void setmData(List<T> data) {
        this.mData = data;
    }

    public int getLayoutId() {
        return layoutId;
    }

    public void setLayoutId(int layoutId) {
        this.layoutId = layoutId;
    }


    /**
     * @param context 上下文
     * @param data    数据源
     * @param id      item的布局资源文件
     */
    public WheelAdapter(Context context, List<T> data, int id) {
        this.mContext = context;
        this.mData = data;
        this.layoutId = id;
    }

    /**
     * 数据源改变，刷新界面
     *
     * @param data
     */
    public void refersh(List<T> data) {
        this.mData = data;
        notifyDataSetChanged();
    }

    @Override
    public int getCount() {
        if (mData != null) {
            return mData.size();
        }
        return 0;
    }

    @Override
    public T getItem(int position) {
        if (mData != null) {
            return mData.get(position);
        }
        return null;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        SimpleAdapterHolder holder = SimpleAdapterHolder.get(convertView, parent, layoutId,
                position);
        covertView(holder, position, mData, getItem(position));
        return holder.getmConvertView();
    }

    /**
     * 子类可重写此方法实现不同的滚动效果
     * @param wheelListView
     * @param selectPosition
     */
    @Override
    public void onHandleIdle(WheelListView wheelListView, int selectPosition) {
        notifyDataSetChanged();
        //精确滚动到某个item的方法，其他的请看api
        wheelListView.smoothScrollToPositionFromTop(selectPosition, 0, 400);
    }

    public abstract void covertView(SimpleAdapterHolder holder, int position, List<T> dataSource, T data);
}

SimpleAdapterHolder其实就是一般的viewHolder

import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * 包名：com.ykbjson.demo.customview.listview
 * 描述：通用viewholder
 * 创建者：yankebin
 * 日期：2016/6/1
 */
public class SimpleAdapterHolder {

    @SuppressWarnings("unused")
    private int mPosition;
    private View mConvertView;
    SparseArray<View> mMembers;

    public View getmConvertView() {
        return mConvertView;
    }

    public SimpleAdapterHolder() {

    }

    private SimpleAdapterHolder(ViewGroup parent, int layoutId, int position) {
        this.mPosition = position;
        this.mMembers = new SparseArray<View>();
        mConvertView = LayoutInflater.from(parent.getContext()).inflate(
                layoutId, parent, false);

        mConvertView.setTag(this);
    }

    public static SimpleAdapterHolder get(View convertView, ViewGroup parent,
            int layoutId, int position) {
        if (convertView == null) {
            return new SimpleAdapterHolder(parent, layoutId, position);
        } else {
            return (SimpleAdapterHolder) convertView.getTag();
        }
    }

    @SuppressWarnings("unchecked")
    public <T extends View> T getView(int viewId) {
        View view = mMembers.get(viewId);
        if (view == null) {
            view = mConvertView.findViewById(viewId);
            mMembers.put(viewId, view);
        }
        return (T) view;
    }
}

为了使用方便，我在外面包装了一层WheelView

package com.ykbjson.demo.customview.listview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Color;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.ImageView;

import com.ykbjson.demo.R;
import com.ykbjson.demo.tools.SLog;

/**
 * 包名：com.ykbjson.demo.customview.otherview
 * 描述：滚轮视图
 * 创建者：yankebin
 * 日期：2016/6/2
 */
public class WheelView extends FrameLayout {
    private WheelListView wheelListView;
    private View mSelectView;

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

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

    public WheelView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView(context, attrs);
    }

    /**
     * 初始化视图
     *
     * @param context
     * @param attrs
     */
    private void initView(Context context, AttributeSet attrs) {
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.WheelView);
        int floatId = typedArray.getResourceId(R.styleable.WheelView_float_layout, -1);
        int bgId = typedArray.getResourceId(R.styleable.WheelView_background_resources, -1);
        SLog.d("bgId : " + bgId);
        typedArray.recycle();
        if (-1 == floatId) {
            throw new IllegalArgumentException("resId is invalid");
        }
        //背景
        ImageView imageView = new ImageView(context);
        imageView.setScaleType(ImageView.ScaleType.FIT_XY);
        try {
            imageView.setLayerType(LAYER_TYPE_SOFTWARE, null);
        } catch (Exception e) {
            e.printStackTrace();
        }

        if (-1 != bgId) {
            imageView.setImageResource(bgId);
        }
        FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(-1, -1);
        addView(imageView, params);

        //listview
        wheelListView = new WheelListView(context);
        wheelListView.setBackgroundColor(Color.TRANSPARENT);
        wheelListView.setClipToPadding(false);
        wheelListView.setClipChildren(false);
        params = new FrameLayout.LayoutParams(-1, -1);
        params.gravity = Gravity.CENTER;
        addView(wheelListView, params);

        //悬浮视图
        mSelectView = LayoutInflater.from(context).inflate(floatId, this, false);
        params = new FrameLayout.LayoutParams(-1, -2);
        params.gravity = Gravity.CENTER;
        addView(mSelectView, params);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        wheelListView.setUp(mSelectView, this);
    }

    public void setAdapter(WheelAdapter adapter) {
        wheelListView.setAdapter(adapter);
    }

    public WheelListView getWheelListView() {
        return wheelListView;
    }
}

定义的属性

 <!-- 仿wheelview的listvie-->
    <declare-styleable name="WheelView">
        <attr name="float_layout" format="reference" />
        <attr name="background_resources" format="reference|color" />
    </declare-styleable>

最后的使用

在xml里

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

    <com.ykbjson.demo.customview.listview.WheelView
        app:float_layout="@layout/layout_scroll_list"
        app:background_resources="@drawable/trip_bg"
        android:id="@+id/wheel"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</FrameLayout>

在代码里

package com.ykbjson.demo.activity;

import android.content.Context;
import android.os.Bundle;
import android.os.Message;
import android.view.View;
import android.widget.TextView;

import com.drivingassisstantHouse.library.base.BaseActivity;
import com.drivingassisstantHouse.library.base.SimpleAdapterHolder;
import com.nineoldandroids.view.ViewHelper;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.ykbjson.demo.R;
import com.ykbjson.demo.bean.AssistantManager;
import com.ykbjson.demo.customview.listview.WheelAdapter;
import com.ykbjson.demo.customview.listview.WheelView;
import com.ykbjson.demo.customview.otherview.CircleImageView;

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

import butterknife.Bind;

/**
 * 包名：com.ykbjson.demo.activity
 * 描述：
 * 创建者：yankebin
 * 日期：2016/5/25
 */
public class TestTravelListActivity extends BaseActivity {
    @Bind(R.id.wheel)
    WheelView wheel;
    private ArrayList<AssistantManager> assistantManagers = new ArrayList<>();
    private TravelListAdapter adapter;


    private void dataChange() {
        adapter = new TravelListAdapter(this, assistantManagers, R.layout.item_assistant_avatar);
        wheel.setAdapter(adapter);

    }


    @Override
    public int bindLayout() {
        return R.layout.activity_scroll_list;
    }

    @Override
    public void initParms(Bundle parms) {

    }


    @Override
    public void initView(View view) {
        for (int i = 0; i < 2; i++) {
            AssistantManager manager = new AssistantManager();
            manager.setMobile("15208279347");
            manager.setName("客服" + i);
            manager.setNickName("简途客户" + i);
            manager.setAssistantId(i);
            manager.setAvatar("drawable://" + R.drawable.customer_service_head);
            manager.setPhoto("drawable://" + R.drawable.ad_page);
            manager.setDescription("呵呵呵呵 的期望的开启电脑去");
            manager.setType(i % 2 == 0 ? 0 : 1);
            manager.setTourismSections("成都-都江堰-青城山");
            assistantManagers.add(manager);
        }
    }


    @Override
    public void doBusiness(Context mContext) {
        baseHandler.sendEmptyMessageDelayed(1, 200);
    }

    @Override
    public void resume() {

    }

    @Override
    public void destroy() {
    }

    @Override
    public void handleMessage(Message msg) {
        dataChange();
    }

    /*主要代码**/
    private class TravelListAdapter extends WheelAdapter<AssistantManager> {
        private int mSelectPosition;

        /**
         * @param context 上下文
         * @param data    数据源
         * @param id      item的布局资源文件
         */
        public TravelListAdapter(Context context, List data, int id) {
            super(context, data, id);
        }

        @Override
        public void onHandleScroll(int selectPosition) {
            mSelectPosition = selectPosition;
            notifyDataSetChanged();
        }

        @Override
        public void covertView(SimpleAdapterHolder holder, int position, List<AssistantManager> dataSource, AssistantManager manager) {
            float scale = 1f;
            if (mSelectPosition == position) {
                scale = 1.2f;
            }
            TextView tvName = holder.getView(R.id.tv_name);
            tvName.setText(manager.getName());
            CircleImageView imageView = holder.getView(R.id.iv_avatar);
            ImageLoader.getInstance().displayImage(manager.getAvatar(), imageView);

            ViewHelper.setScaleX(holder.getmConvertView().findViewById(R.id.layout_content), scale);
            ViewHelper.setScaleY(holder.getmConvertView().findViewById(R.id.layout_content), scale);
        }
    }
}