Android_PullListView

ListView 下拉刷新，上拉加载更多的原理：

（1）主要是onScroll()方法和onTouchEvent()方法，先是onTouchEvent()的ACTION_DOWN,然后是 ACTION_MOVE和onScroll()方法同时进行，最后是onTouchEvent()的ACTION_UP。
（2）刷新的4种状态：CLICK_TO_REFRESH(点击刷新状态，初始状态)、DROP_DOWN_TO_REFRESH(当刷新layout高 度低于一定范围时，为此状态)、RELEASE_TO_REFRESH(当刷新layout高度高于一定范围时，为此状态)、REFRESHING(刷新 中)
（3）onTouchEvent函数：
             ACTION_DOWN时：记录此时touch的点的y坐标，在下面调整高度时使用
             ACTION_MOVE时：此时不断调整header的高度
             ACTION_UP时：根据当前状态决定是进行刷新还是放弃刷新
（4）onScrollStateChanged函数：
              SCROLL_STATE_TOUCH_SCROLL：表示listview正在滚动中，并且手指没有离开屏幕
              SCROLL_STATE_FLING：listview正在滚动中，且手指已经离开屏幕
              SCROLL_STATE_IDLE:停止滚动
（5）onScroll函数：根据listView的当前滚动状态即currentScrollState和当前刷新的状态不断修改header内容显示和刷新状态，如下：
               ListView为SCROLL_STATE_TOUCH_SCROLL且刷新状态不为REFRESHING：
               （a）刷新对应的item可见时，若刷新layout高度超出范围，则置刷新状态为RELEASE_TO_REFRESH；若刷新layout高度低于高度范围，则置刷新状态为DROP_DOWN_TO_REFRESH。

                 （b） 刷新对应的item不可见，重置header

 (6) ListView为SCROLL_STATE_FLING状态(松手滚动中)

　　　　　　　　（a） 若刷新对应的item可见并且刷新状态不为REFRESHING，设置position为1的(即第二个)item可见

　　　　　　　　（b） 若反弹回来，设置position为1的(即第二个)item可见

import java.text.SimpleDateFormat;
import java.util.Date;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.LinearInterpolator;
import android.view.animation.RotateAnimation;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

/**
 * @author kchang
 * @E-mail:kchang244@163.com
 */
public class PullListView extends ListView implements OnScrollListener {
    private static final String TAG = PullListView.class.getSimpleName();
    //hear view 的四种状态
    /**静止的状态*/
    private final static int NONE = 0;
    /**下拉刷新的状态，文字信息提示下拉刷新，箭头朝下*/
    private final static int PULL = 1;
    /**下拉刷新的状态，文字提示松开后刷新，箭头朝上*/
    private final static int RELEASE = 2;
    /**正在刷新数据，提示正在刷新数据，没有箭头，显示圆形进度条*/
    private final static int REFRESHING = 3;
    
    //区分当前操作是刷新还是加载
    /**刷新*/
    private final static int REFERSH = 0;
    /**加载数据*/
    private final static int LOAD = 1;
    
    //区分pull和release的距离的大小
    private final static int SPACE = 20;
    
    //状态
    private int state ;
    
    private LayoutInflater layoutInflater;
    private View headView;//listview头部view
    private View footView;//listView底部view
    private TextView  tipTv;//显示提示信息
    private TextView lastUpdateTv;//显示最后加载的时间
    private ImageView arrow;
    private ProgressBar progressBar;//圆形进度条提示状态
    
    private TextView loadFullTv;//数据加载失败
    private TextView noDataTv;///没有数据
    private TextView moreTv;//加载更多数据
    private ProgressBar loadPb;//显示加载数据的状态 
    
    private RotateAnimation animation;
    private RotateAnimation reverseAnimation;
    
    private int startY;//按下的Y轴位置
    
    private int firstVisibleItem;
    private int scrollState;//滚动的状态
    private int headerContentInitialHeight;// 头部view初始化高度
    private int headerContentHeight;//头部内容的高度
    
    /***只有在listview第一个item显示的时候才进行下来刷新，否则此时的下拉只是滚动listview*/
    private boolean isRecodered;
    //判断是否正在加载
    private boolean isLoading;
    //开启或者关闭加载更多功能
    private boolean isLoadEnable = true;
    private boolean isLoadFull;
    /**分页加载一次加载的数据大小*/
    private int pageSize = 10;
    
    private OnLoadListener onLoadListener;
    
    private OnRefershListener onRefershListener; 
    
    public PullListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView(context);
    }
    public PullListView(Context context, AttributeSet attrs,int defStyle) {
        super(context, attrs,defStyle);
        initView(context);
    }
    public PullListView (Context context) {
        super(context);
        initView(context);
        
    }
      // 设置下拉刷新监听  
    public void setOnRefreshListener(OnRefershListener onRefreshListener) {  
        this.onRefershListener = onRefreshListener;  
    }  
  
    // 设置加载更多监听  
    public void setOnLoadListener(OnLoadListener onLoadListener) {  
        this.isLoadEnable = true;  
        this.onLoadListener = onLoadListener;  
    }  
    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        //SCROLL_STATE_TOUCH_SCROLL 1表示listview正在滚动中，并且手指没有离开屏幕
        //SCROLL_STATE_FLING 2：listview正在滚动中，且手指已经离开屏幕
        //SCROLL_STATE_IDLE 0:停止滚动
        this.scrollState = scrollState;
        ifNeedLoad(view, scrollState);
        Log.d(TAG, "onScrollStateChanged");
    }
    
     // 根据listview滑动的状态判断是否需要加载更多  
    private void ifNeedLoad(AbsListView view, int scrollState) {  
        if (!isLoadEnable) {  
            return;  
        }  
        try {  
            if (scrollState == OnScrollListener.SCROLL_STATE_IDLE  
                    && !isLoading  
                    && view.getLastVisiblePosition() == view  
                            .getPositionForView(footView) && !isLoadFull) {  
                onLoadData();  
                isLoading = true;  
            }  
        } catch (Exception e) {  
            e.printStackTrace();
        }  
    }  
    
    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {
        this.firstVisibleItem = firstVisibleItem;
        Log.d(TAG, "onScroll");
    }
    /***
     * 是否开启加载更多
     * @return
     *         true表示开启，false表示不加载
     */
    public boolean isLoadEnable() {  
        return isLoadEnable;  
    }  
     // 这里的开启或者关闭加载更多，并不支持动态调整  
    public void setLoadEnable(boolean loadEnable) {  
        this.isLoadEnable = loadEnable;  
        this.removeFooterView(footView);  
    }  
    public int getPageSize() {  
        return pageSize;  
    }  
  
    public void setPageSize(int pageSize) {  
        this.pageSize = pageSize;  
    }  
    // 初始化组件  
    private void initView(Context context) {  
  
        // 设置箭头特效  
        animation = new RotateAnimation(0, -180,  
                RotateAnimation.RELATIVE_TO_SELF, 0.5f,  
                RotateAnimation.RELATIVE_TO_SELF, 0.5f);  
        animation.setInterpolator(new LinearInterpolator());  
        animation.setDuration(100);  
        animation.setFillAfter(true);  
  
        reverseAnimation = new RotateAnimation(-180, 0,  
                RotateAnimation.RELATIVE_TO_SELF, 0.5f,  
                RotateAnimation.RELATIVE_TO_SELF, 0.5f);  
        reverseAnimation.setInterpolator(new LinearInterpolator());  
        reverseAnimation.setDuration(100);  
        reverseAnimation.setFillAfter(true);  
  
        layoutInflater = LayoutInflater.from(context);  
        footView = layoutInflater.inflate(R.layout.listview_footer, null);  
        loadFullTv = (TextView) footView.findViewById(R.id.loadFull);  
        noDataTv = (TextView) footView.findViewById(R.id.noData);  
        moreTv = (TextView) footView.findViewById(R.id.more);  
        loadPb = (ProgressBar) footView.findViewById(R.id.loading);  
  
        headView = layoutInflater.inflate(R.layout.pull_to_refresh_header, null);  
        arrow = (ImageView) headView.findViewById(R.id.arrow);  
        tipTv = (TextView) headView.findViewById(R.id.tip);  
        lastUpdateTv = (TextView) headView.findViewById(R.id.lastUpdate);  
        progressBar = (ProgressBar) headView.findViewById(R.id.refreshing);  
  
        // 为listview添加头部和尾部，并进行初始化  
        headerContentInitialHeight = headView.getPaddingTop();  
        measureView(headView);  
        
        headerContentHeight = headView.getMeasuredHeight();  
        topPadding(-headerContentHeight);  
        
        this.addHeaderView(headView);  
        this.addFooterView(footView);  
        this.setOnScrollListener(this);  
    }  
    // 调整header的大小。其实调整的只是距离顶部的高度。  
    private void topPadding(int topPadding) {  
        headView.setPadding(headView.getPaddingLeft(), topPadding,  
                headView.getPaddingRight(), headView.getPaddingBottom());  
        headView.invalidate();  
    } 
    
    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
        case MotionEvent.ACTION_DOWN:
            if (firstVisibleItem == 0) {
                isRecodered = true;
                startY =  (int)ev.getY();
            }
            break;
        case MotionEvent.ACTION_MOVE:
            //下拉刷新重点
            whenMove(ev);
            break;
        case MotionEvent.ACTION_UP:
            if (state == PULL) {
                  Log.d(TAG, "ACTION_UP PULL");
                state = NONE;
                refreshHeaderViewByState();
            } else if (state == RELEASE) {//提示用户松开手后刷新数据
                Log.d(TAG, "ACTION_UP RELEASE");
                state = REFRESHING;
                refreshHeaderViewByState();
                onRefersh();
            }
            break;
        case MotionEvent.ACTION_CANCEL:
            break;

        default:
            break;
        }
        return super.onTouchEvent(ev);
    }
    // 解读手势，刷新header状态  
    private void whenMove(MotionEvent ev) {  
        if (!isRecodered) {  
            return;  
        }  
        
        int tmpY = (int) ev.getY();  
        int space = tmpY - startY;  
        int topPadding = space - headerContentHeight;  
        switch (state) {  
        case NONE:  
            if (space > 0) {  
                state = PULL;  
                refreshHeaderViewByState();  
            }  
            Log.d(TAG, "whenMove NONE");
            break;  
        case PULL:  
            Log.d(TAG, "whenMove PULL");
            topPadding(topPadding);  
            if (scrollState == SCROLL_STATE_TOUCH_SCROLL  
                    && space > headerContentHeight + SPACE) {  
                state = RELEASE;  
                refreshHeaderViewByState();  
            }  
            break;  
        case RELEASE:  
               Log.d(TAG, "whenMove RELEASE");
            topPadding(topPadding);  
            if (space > 0 && space < headerContentHeight + SPACE) {  
                state = PULL;  
                refreshHeaderViewByState();  
            } else if (space <= 0) {  
                state = NONE;  
                refreshHeaderViewByState();  
            }  
            break;  
        }  
  
    }  
    /** 
     * 这个方法是根据结果的大小来决定footer显示的。 
     * <p> 
     * 这里假定每次请求的条数为10。如果请求到了10条。则认为还有数据。如过结果不足10条，则认为数据已经全部加载，这时footer显示已经全部加载 
     * </p> 
     *  
     * @param resultSize 
     */  
    public void setResultSize(int resultSize) {  
        if (resultSize == 0) {  
            isLoadFull = true;  
            loadFullTv.setVisibility(View.GONE);  
            loadPb.setVisibility(View.GONE);  
            moreTv.setVisibility(View.GONE);  
            noDataTv.setVisibility(View.VISIBLE);  
        } else if (resultSize > 0 && resultSize < pageSize) {  
            isLoadFull = true;  
            loadFullTv.setVisibility(View.VISIBLE);  
            loadPb.setVisibility(View.GONE);  
            moreTv.setVisibility(View.GONE);  
            noDataTv.setVisibility(View.GONE);  
        } else if (resultSize == pageSize) {  
            isLoadFull = false;  
            loadFullTv.setVisibility(View.GONE);  
            loadPb.setVisibility(View.VISIBLE);  
            moreTv.setVisibility(View.VISIBLE);  
            noDataTv.setVisibility(View.GONE);  
        }  
  
    }  

     // 用来计算header大小的。
    private void measureView(View child) {  
        ViewGroup.LayoutParams p = child.getLayoutParams();  
        if (p == null) {  
            p = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,  
                    ViewGroup.LayoutParams.WRAP_CONTENT);  
        }  
        int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0, p.width);  
        int lpHeight = p.height;  
        int childHeightSpec;  
        if (lpHeight > 0) {  
            childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight,  
                    MeasureSpec.EXACTLY);  
        } else {  
            childHeightSpec = MeasureSpec.makeMeasureSpec(0,  
                    MeasureSpec.UNSPECIFIED);  
        }  
        child.measure(childWidthSpec, childHeightSpec);  
    }  
      /***
       * 执行刷新数据的方法
       */
    public void onRefersh() {
        if (null != onRefershListener) {
            onRefershListener.onRefersh();
        }
    }
    /**
     * 执行加载数据的方法
     */
    public void onLoadData() {
        if (null != onLoadListener) {
            onLoadListener.onLoad();
        }
    }
    // 用于加载更多结束后的回调  
    public void onLoadComplete() {  
        isLoading = false;  
    }  
    /**
     * 刷新完以后的方法
     * @param updateTime
     *             当前是时间
     */
    public void onRefershComplete(String updateTime) {
        lastUpdateTv.setText(getResources().getString(R.string.lastUpdateTime, updateTime));
        state = NONE;
        refreshHeaderViewByState();
    } 
    /**
     * 刷新数据完毕
     */
    public void onRefershComlete() {
        String currentTiem = getCurrentTime();
        onRefershComplete(currentTiem);
    }
    /**
     * 获取当前的时间
     * @return
     */
    private String getCurrentTime() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        return dateFormat.format(new Date());
    }
    /***
     *  根据当前状态，调整header
     * */  
    private void refreshHeaderViewByState() {  
        switch (state) {  
        case NONE:  //原始状态
            Log.d(TAG, "refreshHeaderViewByState NONE");
            topPadding(-headerContentHeight);  
            tipTv.setText(R.string.pull_to_refresh);  
            progressBar.setVisibility(View.GONE);  
            arrow.clearAnimation();  
            arrow.setImageResource(R.drawable.pull_to_refresh_arrow);  
            break;  
        case PULL:  //箭头朝下
            Log.d(TAG, "refreshHeaderViewByState PULL");
            arrow.setVisibility(View.VISIBLE);  
            tipTv.setVisibility(View.VISIBLE);  
            lastUpdateTv.setVisibility(View.VISIBLE);  
            progressBar.setVisibility(View.GONE);  
            tipTv.setText(R.string.pull_to_refresh);  
            arrow.clearAnimation();  
            arrow.setAnimation(reverseAnimation);  
            break;  
        case RELEASE:  //箭头朝上
            Log.d(TAG, "refreshHeaderViewByState RELEASE");
            arrow.setVisibility(View.VISIBLE);  
            tipTv.setVisibility(View.VISIBLE);  
            lastUpdateTv.setVisibility(View.VISIBLE);  
            progressBar.setVisibility(View.GONE);  
            tipTv.setText(R.string.pull_to_refresh);  
            tipTv.setText(R.string.release_to_refresh);  
            arrow.clearAnimation();  
            arrow.setAnimation(animation);  
            break;  
        case REFRESHING:  //显示数据加载的圆形进度条
            Log.d(TAG, "refreshHeaderViewByState REFRESHING");
            topPadding(headerContentInitialHeight);  
            progressBar.setVisibility(View.VISIBLE);  
            arrow.clearAnimation();  
            arrow.setVisibility(View.GONE);  
            tipTv.setVisibility(View.GONE);  
            lastUpdateTv.setVisibility(View.GONE);  
            break;  
        }  
    }  
    /**
     * 下拉刷新的接口
     *
     */
    public interface OnRefershListener {
        void onRefersh();
    }
    /**
     * 定义加载更多的接口
     */
    public interface OnLoadListener {
        void onLoad();
    }
}