前言
使用ViewDragHelper实现肯定可以实现下拉刷新，而且可以通过这种场景可以举一反三出很多其他的场景。
实现步骤
1.首先看一下布局文件
PullToRefreshLayout是个ViewGroup，它下面有一个子类，这个子类下又包含两个子类，一个就是head部分，一个就是ListView部分
2.接下来看PullToRefreshLayout的实现
import android.content.Context;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AbsListView;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.TextView;
import com.xsh.customviewstudy.R;
public class PullToRefreshLayout extends LinearLayout {
private final String TAG="PullToRefreshLayout";
/**
* 下拉状态
*/
public static final int STATUS_PULL_TO_REFRESH = 0;
/**
* 释放立即刷新状态
*/
public static final int STATUS_RELEASE_TO_REFRESH = 1;
/**
* 正在刷新状态
*/
public static final int STATUS_REFRESHING = 2;
/**
* 刷新完成或未刷新状态
*/
public static final int STATUS_REFRESH_FINISHED = 3;
/**
* 下拉头的View
*/
private View header;
/**
* 刷新时显示的进度条
*/
private ProgressBar progressBar;
/**
* 指示下拉和释放的文字描述
*/
private TextView description;
/**
* 下拉头的布局参数
*/
private MarginLayoutParams headerLayoutParams;
/**
* 当前处理什么状态，可选值有STATUS_PULL_TO_REFRESH, STATUS_RELEASE_TO_REFRESH,
* STATUS_REFRESHING 和 STATUS_REFRESH_FINISHED
*/
private int currentStatus = STATUS_REFRESH_FINISHED;;
/**
* 记录上一次的状态是什么，避免进行重复操作
*/
private int lastStatus = currentStatus;
/**
* 用于处理事件分发的mDragger
*/
private ViewDragHelper mDragger;
/**
* 需要去下拉刷新的ListView
*/
private AbsListView listView;
private LinearLayout pullLayout;
/**
* 下拉头的高度
*/
private int hideHeaderHeight;
/**
* 当前滑动的距离
*/
private int currentTop;
/**
* 允许滑动的最大距
*/
private int maxDragHeight;
/**
* 是否加载过
*/
private boolean loadOnce=false;
private boolean isTouch=false;
private PullToRefreshListener pullToRefreshListener;
public PullToRefreshLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
if(changed && !loadOnce){
maxDragHeight=getMeasuredHeight()/2;
hideHeaderHeight = -header.getHeight();
headerLayoutParams = (MarginLayoutParams) pullLayout.getLayoutParams();
headerLayoutParams.topMargin = hideHeaderHeight;
loadOnce = true;
}
}
@Override
public void computeScroll() {
super.computeScroll();
if(mDragger.continueSettling(true)){
invalidate();
}
}
/**
* 设置刷新回调接口
* @param listener
*/
public void setPullToRefreshistener(PullToRefreshListener listener){
this.pullToRefreshListener=listener;
}
/**
* 完成刷新
*/
public void finishPullToRefresh(){
currentStatus=STATUS_REFRESH_FINISHED;
mDragger.smoothSlideViewTo(pullLayout, 0, hideHeaderHeight);
invalidate();
}
/**
* 初始化view
*/
private void init(){
pullLayout=(LinearLayout) getChildAt(0);
listView = (AbsListView) pullLayout.getChildAt(1);
header = pullLayout.getChildAt(0);
progressBar = (ProgressBar) header.findViewById(R.id.progress_bar);
description = (TextView) header.findViewById(R.id.description);
mDragger=ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
/**
* 进行捕获拦截，那些View可以进行drag操作
* @param childView
* @param position
* @return 直接返回true，拦截所有的VIEW
*/
@Override
public boolean tryCaptureView(View childView, int position) {
Log.i(TAG, "tryCaptureView");
isTouch=true;
return childView==pullLayout && isTop() ;
}
@Override
public int clampViewPositionVertical(View child, int top, int dy) {
Log.i(TAG, "clampViewPositionVertical: top="+top+"dy="+dy+"hideHeaderHeight="+hideHeaderHeight+"maxDragHeight="+maxDragHeight);
if(top<=hideHeaderHeight){
return hideHeaderHeight;
}else if(top>maxDragHeight){
return maxDragHeight;
}
return top;
}
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
Log.i(TAG, "onViewReleased");
super.onViewReleased(releasedChild, xvel, yvel);
if (releasedChild == pullLayout){
isTouch=false;
if (currentStatus == STATUS_RELEASE_TO_REFRESH ) {
// 松手时如果是释放立即刷新状态，就去调用正在刷新的任务
currentStatus = STATUS_REFRESHING;
updateHeadView();
mDragger.settleCapturedViewAt(0,0);
invalidate();
if(pullToRefreshListener!=null){
pullToRefreshListener.onRefresh();
}
}else if(currentStatus == STATUS_PULL_TO_REFRESH ){
mDragger.settleCapturedViewAt(0,hideHeaderHeight);
invalidate();
}else if(currentStatus == STATUS_REFRESHING){
mDragger.settleCapturedViewAt(0,0);
invalidate();
}
}
}
@Override
public void onViewPositionChanged(View changedView, int left,
int top, int dx, int dy) {
super.onViewPositionChanged(changedView, left, top, dx, dy);
Log.i(TAG, "onViewPositionChanged: top="+top);
currentTop=top;
if (isTouch && currentStatus != STATUS_REFRESHING){
if (currentTop <0) {
currentStatus = STATUS_PULL_TO_REFRESH;
} else {
currentStatus = STATUS_RELEASE_TO_REFRESH;
}
updateHeadView();
lastStatus=currentStatus;
}
}
@Override
public int getViewVerticalDragRange(View child) {
return maxDragHeight;
}
});
}
private void updateHeadView(){
if(lastStatus!=currentStatus){
if (currentStatus == STATUS_PULL_TO_REFRESH) {
description.setText(getResources().getString(R.string.pull_to_refresh));
progressBar.setVisibility(View.GONE);
} else if (currentStatus == STATUS_RELEASE_TO_REFRESH) {
description.setText(getResources().getString(R.string.release_to_refresh));
progressBar.setVisibility(View.GONE);
} else if (currentStatus == STATUS_REFRESHING) {
description.setText(getResources().getString(R.string.refreshing));
progressBar.setVisibility(View.VISIBLE);
}
}
}
private boolean isTop(){
return listView.getFirstVisiblePosition() == 0
&& getScrollY() <= listView.getMeasuredHeight();
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
return mDragger.shouldInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
mDragger.processTouchEvent(event);
return true;
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
init();
}
public interface PullToRefreshListener {
/**
* 下拉刷新时调用
*/
void onRefresh();
/**
* 上拉加载更多的刷新
*/
// void onLoadMoreRefresh();
}
}
1.protected void onFinishInflate() ：实例化各个子View，比如LinearLayout，ListView，progressBar等等
实例化ViewDragHelper
2.protected void onLayout(boolean changed, int l, int t, int r, int b) : 把head隐藏起来
3.其他部分就没什么好的，so easy
源码参考我的github地址
参考文章
http://blog.csdn.net/liuwang521/article/details/52764520