本文详细解析了早期下拉刷新组件XListView的局限性及替代方案PullToRefreshLayout的实现原理，包括状态转换、触摸事件处理等核心逻辑，并对比介绍了Google官方SwipeRefreshLayout组件的使用方法。
早期下拉刷新主要是用XListView，这个类是继承ListView的，使用起来有局限性，并且在git上作者已经不维护了，之后有人自己写了一个PullToRefreshLayout，不用再继承自ListView，而是直接嵌套在所有继承于AbsListView的外面，如下：
<com.fq.pulltorefresh.PullToRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/refresh_view"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<include layout="@layout/refresh_head" />
<!-- 支持AbsListView的所有子类 -->
<ListView
android:id="@+id/content_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/white"
android:divider="@color/gray"
android:dividerHeight="1dp" >
</ListView>
</com.fq.pulltorefresh.PullToRefreshLayout>首先说明PullToRefreshLayout这个类不是我写的，是别人写的，我这里直接拿过来，然后稍微给大家讲解下，在讲解这个类之前，先画图分析下下拉刷新的实现逻辑：
package com.fq.pulltorefresh;
import java.lang.reflect.Field;
import java.util.Timer;
import java.util.TimerTask;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.LinearGradient;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.RectF;
import android.graphics.Shader.TileMode;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.view.animation.AnimationUtils;
import android.view.animation.LinearInterpolator;
import android.view.animation.RotateAnimation;
import android.widget.AbsListView;
import android.widget.RelativeLayout;
import android.widget.TextView;
public class PullToRefreshLayout extends RelativeLayout implements OnTouchListener
{
public static final String TAG = "PullToRefreshLayout";
// 下拉刷新
public static final int PULL_TO_REFRESH = 0;
// 释放刷新
public static final int RELEASE_TO_REFRESH = 1;
// 正在刷新
public static final int REFRESHING = 2;
// 刷新完毕
public static final int DONE = 3;
// 当前状态
private int state = PULL_TO_REFRESH;
// 刷新回调接口
private OnRefreshListener mListener;
// 刷新成功
public static final int REFRESH_SUCCEED = 0;
// 刷新失败
public static final int REFRESH_FAIL = 1;
// 下拉头
private View headView;
// 内容
private View contentView;
// 按下Y坐标，上一个事件点Y坐标
private float downY, lastY;
// 下拉的距离
public float moveDeltaY = 0;
// 释放刷新的距离
private float refreshDist = 200;
private Timer timer;
private MyTimerTask mTask;
// 回滚速度
public float MOVE_SPEED = 8;
// 第一次执行布局
private boolean isLayout = false;
// 是否可以下拉
private boolean canPull = true;
// 在刷新过程中滑动操作
private boolean isTouchInRefreshing = false;
// 手指滑动距离与下拉头的滑动距离比，中间会随正切函数变化
private float radio = 2;
// 下拉箭头的转180°动画
private RotateAnimation rotateAnimation;
// 均匀旋转动画
private RotateAnimation refreshingAnimation;
// 下拉的箭头
private View pullView;
// 正在刷新的图标
private View refreshingView;
// 刷新结果图标
private View stateImageView;
// 刷新结果：成功或失败
private TextView stateTextView;
/**
* 执行自动回滚的handler
*/
Handler updateHandler = new Handler()
{
@Override
public void handleMessage(Message msg)
{
Log.e("fuqiang","handleMessage");
// 回弹速度随下拉距离moveDeltaY增大而增大
MOVE_SPEED = (float) (8 + 5 * Math.tan(Math.PI / 2 / getMeasuredHeight() * moveDeltaY));
if (state == REFRESHING && moveDeltaY <= refreshDist && !isTouchInRefreshing)
{
moveDeltaY = refreshDist;
mTask.cancel();
}
if (canPull)
moveDeltaY -= MOVE_SPEED;
if (moveDeltaY <= 0)
{
// 已完成回弹
moveDeltaY = 0;
pullView.clearAnimation();
if (state != REFRESHING)
changeState(PULL_TO_REFRESH);
mTask.cancel();
}
requestLayout();
}
};
public void setOnRefreshListener(OnRefreshListener listener)
{
mListener = listener;
}
public PullToRefreshLayout(Context context)
{
super(context);
initView(context);
}
public PullToRefreshLayout(Context context, AttributeSet attrs)
{
super(context, attrs);
initView(context);
}
public PullToRefreshLayout(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
initView(context);
}
private void initView(Context context)
{
timer = new Timer();
mTask = new MyTimerTask(updateHandler);
rotateAnimation = (RotateAnimation) AnimationUtils.loadAnimation(context, R.anim.reverse_anim);
refreshingAnimation = (RotateAnimation) AnimationUtils.loadAnimation(context, R.anim.rotating);
// 添加匀速转动动画
LinearInterpolator lir = new LinearInterpolator();
rotateAnimation.setInterpolator(lir);
refreshingAnimation.setInterpolator(lir);
}
private void hideHead()
{
if (mTask != null)
{
mTask.cancel();
mTask = null;
}
mTask = new MyTimerTask(updateHandler);
timer.schedule(mTask,0,5);
}
/**
* 完成刷新操作，显示刷新结果
*/
public void refreshFinish(int refreshResult)
{
refreshingView.clearAnimation();
refreshingView.setVisibility(View.GONE);
switch (refreshResult)
{
case REFRESH_SUCCEED:
// 刷新成功
stateImageView.setVisibility(View.VISIBLE);
stateTextView.setText(R.string.refresh_succeed);
stateImageView.setBackgroundResource(R.drawable.refresh_succeed);
break;
case REFRESH_FAIL:
// 刷新失败
stateImageView.setVisibility(View.VISIBLE);
stateTextView.setText(R.string.refresh_fail);
stateImageView.setBackgroundResource(R.drawable.refresh_failed);
break;
default:
break;
}
// 刷新结果停留1秒
new Handler()
{
@Override
public void handleMessage(Message msg)
{
state = PULL_TO_REFRESH;
hideHead();
}
}.sendEmptyMessageDelayed(0, 1000);
}
private void changeState(int to)
{
state = to;
switch (state)
{
case PULL_TO_REFRESH:
// 下拉刷新
stateImageView.setVisibility(View.GONE);
stateTextView.setText(R.string.pull_to_refresh);
pullView.clearAnimation();
pullView.setVisibility(View.VISIBLE);
break;
case RELEASE_TO_REFRESH:
// 释放刷新
stateTextView.setText(R.string.release_to_refresh);
pullView.startAnimation(rotateAnimation);
break;
case REFRESHING:
// 正在刷新
pullView.clearAnimation();
refreshingView.setVisibility(View.VISIBLE);
pullView.setVisibility(View.INVISIBLE);
refreshingView.startAnimation(refreshingAnimation);
stateTextView.setText(R.string.refreshing);
break;
default:
break;
}
}
/*
* （非 Javadoc）由父控件决定是否分发事件，防止事件冲突
*
* @see android.view.ViewGroup#dispatchTouchEvent(android.view.MotionEvent)
*/
@Override
public boolean dispatchTouchEvent(MotionEvent ev)
{
switch (ev.getActionMasked())
{
case MotionEvent.ACTION_DOWN:
downY = ev.getY();
lastY = downY;
if (mTask != null)
{
mTask.cancel();
}
Log.e("fuqiang","ev.getY()" + ev.getY());
Log.e("fuqiang","moveDeltaY" + moveDeltaY);
if (ev.getY() < moveDeltaY)
return true;
break;
case MotionEvent.ACTION_MOVE:
if (canPull)
{
// 对实际滑动距离做缩小，造成用力拉的感觉
moveDeltaY = moveDeltaY + (ev.getY() - lastY) / radio;
if (moveDeltaY < 0)
moveDeltaY = 0;
if (moveDeltaY > getMeasuredHeight())
moveDeltaY = getMeasuredHeight();
if (state == REFRESHING)
{
isTouchInRefreshing = true;
}
lastY = ev.getY();
// 根据下拉距离改变比例
radio = (float) (2 + 2 * Math.tan(Math.PI / 2 / getMeasuredHeight() * moveDeltaY));
requestLayout();
}
if (moveDeltaY <= refreshDist && state == RELEASE_TO_REFRESH)
{
changeState(PULL_TO_REFRESH);
}
if (moveDeltaY >= refreshDist && state == PULL_TO_REFRESH)
{
changeState(RELEASE_TO_REFRESH);
}
if (moveDeltaY > 8)
{
// 防止下拉过程中误触发长按事件和点击事件
clearContentViewEvents();
}
if (moveDeltaY > 0)
{
return true;
}
break;
case MotionEvent.ACTION_UP:
if (moveDeltaY > refreshDist)
// 正在刷新时往下拉释放后下拉头不隐藏
isTouchInRefreshing = false;
if (state == RELEASE_TO_REFRESH)
{
changeState(REFRESHING);
// 刷新操作
if (mListener != null)
mListener.onRefresh();
} else
{
}
hideHead();
default:
break;
}
// 事件分发交给父类
return super.dispatchTouchEvent(ev);
}
/**
* 通过反射修改字段去掉长按事件和点击事件
*/
private void clearContentViewEvents()
{
try
{
Field[] fields = AbsListView.class.getDeclaredFields();
for (int i = 0; i < fields.length; i++)
if (fields[i].getName().equals("mPendingCheckForLongPress"))
{
// mPendingCheckForLongPress是AbsListView中的字段，通过反射获取并从消息列表删除，去掉长按事件
fields[i].setAccessible(true);
contentView.getHandler().removeCallbacks((Runnable) fields[i].get(contentView));
} else if (fields[i].getName().equals("mTouchMode"))
{
// TOUCH_MODE_REST = -1， 这个可以去除点击事件
fields[i].setAccessible(true);
fields[i].set(contentView, -1);
}
// 去掉焦点
((AbsListView) contentView).getSelector().setState(new int[]
{ 0 });
} catch (Exception e)
{
Log.d(TAG, "error : " + e.toString());
}
}
/*
* （非 Javadoc）绘制阴影效果，颜色值可以修改
*
* @see android.view.ViewGroup#dispatchDraw(android.graphics.Canvas)
*/
@Override
protected void dispatchDraw(Canvas canvas)
{
super.dispatchDraw(canvas);
if (moveDeltaY == 0)
return;
RectF rectF = new RectF(0, 0, getMeasuredWidth(), moveDeltaY);
Paint paint = new Paint();
paint.setAntiAlias(true);
// 阴影的高度为26
LinearGradient linearGradient = new LinearGradient(0, moveDeltaY, 0, moveDeltaY - 26, 0x66000000, 0x00000000, TileMode.CLAMP);
paint.setShader(linearGradient);
paint.setStyle(Style.FILL);
canvas.drawRect(rectF, paint);
}
private void initView()
{
pullView = headView.findViewById(R.id.pull_icon);
stateTextView = (TextView) headView.findViewById(R.id.state_tv);
refreshingView = headView.findViewById(R.id.refreshing_icon);
stateImageView = headView.findViewById(R.id.state_iv);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
if (!isLayout)
{
headView = getChildAt(0);
contentView = getChildAt(1);
contentView.setOnTouchListener(this);
isLayout = true;
initView();
refreshDist = ((ViewGroup) headView).getChildAt(0).getMeasuredHeight();
}
if (canPull)
{
// 改变子控件的布局
headView.layout(0, (int) moveDeltaY - headView.getMeasuredHeight(), headView.getMeasuredWidth(), (int) moveDeltaY);
contentView.layout(0, (int) moveDeltaY, contentView.getMeasuredWidth(), (int) moveDeltaY + contentView.getMeasuredHeight());
} else
super.onLayout(changed, l, t, r, b);
}
class MyTimerTask extends TimerTask
{
Handler handler;
public MyTimerTask(Handler handler)
{
this.handler = handler;
}
@Override
public void run()
{
handler.sendMessage(handler.obtainMessage());
}
}
@Override
public boolean onTouch(View v, MotionEvent event)
{
Log.e("fuqiang","onTouch被执行了");
// 第一个item可见且滑动到顶部
AbsListView alv = null;
try
{
alv = (AbsListView) v;
} catch (Exception e)
{
Log.d(TAG, e.getMessage());
return false;
}
if (alv.getCount() == 0)
{
canPull = true;
} else if (alv.getFirstVisiblePosition() == 0 && alv.getChildAt(0).getTop() >= 0)
{
canPull = true;
} else
canPull = false;
return false;
}
}
if (canPull)
{
// 改变子控件的布局
headView.layout(0, (int) moveDeltaY - headView.getMeasuredHeight(), headView.getMeasuredWidth(), (int) moveDeltaY);
contentView.layout(0, (int) moveDeltaY, contentView.getMeasuredWidth(), (int) moveDeltaY + contentView.getMeasuredHeight());在onLayout里，初始摆放的时候，moveDeltaY 是0，相当于把headView放在了Y轴的负坐标，这样就隐藏在上面了，下面分析dispatchTouchEvent方法：
@Override
public boolean dispatchTouchEvent(MotionEvent ev)
{
switch (ev.getActionMasked())
{
case MotionEvent.ACTION_DOWN:
downY = ev.getY();
lastY = downY;
if (mTask != null)
{
mTask.cancel();
}
Log.e("fuqiang","ev.getY()" + ev.getY());
Log.e("fuqiang","moveDeltaY" + moveDeltaY);
if (ev.getY() < moveDeltaY)
return true;
break;
case MotionEvent.ACTION_MOVE:
if (canPull)
{
// 对实际滑动距离做缩小，造成用力拉的感觉
moveDeltaY = moveDeltaY + (ev.getY() - lastY) / radio;
if (moveDeltaY < 0)
moveDeltaY = 0;
if (moveDeltaY > getMeasuredHeight())
moveDeltaY = getMeasuredHeight();
if (state == REFRESHING)
{
isTouchInRefreshing = true;
}
lastY = ev.getY();
// 根据下拉距离改变比例
radio = (float) (2 + 2 * Math.tan(Math.PI / 2 / getMeasuredHeight() * moveDeltaY));
requestLayout();
}
if (moveDeltaY <= refreshDist && state == RELEASE_TO_REFRESH)
{
changeState(PULL_TO_REFRESH);
}
if (moveDeltaY >= refreshDist && state == PULL_TO_REFRESH)
{
changeState(RELEASE_TO_REFRESH);
}
if (moveDeltaY > 8)
{
// 防止下拉过程中误触发长按事件和点击事件
clearContentViewEvents();
}
if (moveDeltaY > 0)
{
return true;
}
break;
case MotionEvent.ACTION_UP:
if (moveDeltaY > refreshDist)
// 正在刷新时往下拉释放后下拉头不隐藏
isTouchInRefreshing = false;
if (state == RELEASE_TO_REFRESH)
{
changeState(REFRESHING);
// 刷新操作
if (mListener != null)
mListener.onRefresh();
} else
{
}
hideHead();
default:
break;
}
// 事件分发交给父类
return super.dispatchTouchEvent(ev);
}我们可以看到关键点就是改变moveDeltaY 的值，然后调用requestLayout，这样就会重新调用onLayout函数，来改变容器中两个View的位置，达到效果，dispatchTouchEvent返回true的话，就不会把事件传递给子View，我们看到在moveDeltaY>0的时候，返回了true，接下来的移动事件都由父类来消费，在抬起的时候才会传递给子View。
在onLayout里有这么一句contentView.setOnTouchListener(this);那么这个父类重写的onTouch，其实是给了子类，子类的onTouch里判断是否到顶了，如果是，就可以下拉，否则就不能下拉，不能下拉的话，事件就传递给子View，子View自己消费了，其他逻辑我就不分析了，代码还是写的很清楚了，用起来也很方便：
package com.fq.pulltorefresh;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.animation.AnimationUtils;
import android.view.animation.LinearInterpolator;
import android.view.animation.RotateAnimation;
import android.widget.AbsListView;
import android.widget.ListView;
public class MainActivity extends Activity implements OnRefreshListener
{
private AbsListView alv;
private PullToRefreshLayout refreshLayout;
private RotateAnimation loadingAnimation;
private MyAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
init();
}
private void init()
{
alv = (AbsListView) findViewById(R.id.content_view);
refreshLayout = (PullToRefreshLayout) findViewById(R.id.refresh_view);
refreshLayout.setOnRefreshListener(this);
initListView();
loadingAnimation = (RotateAnimation) AnimationUtils.loadAnimation(this, R.anim.rotating);
LinearInterpolator lir = new LinearInterpolator();
loadingAnimation.setInterpolator(lir);
}
private void initListView()
{
List<String> items = new ArrayList<String>();
for (int i = 0; i < 30; i++)
{
items.add("MyListView item " + i);
}
View headView = getLayoutInflater().inflate(R.layout.listview_head, null);
((ListView) alv).addHeaderView(headView, null, false);
adapter = new MyAdapter(this, items);
alv.setAdapter(adapter);
}
@Override
public void onRefresh()
{
new Handler()
{
@Override
public void handleMessage(Message msg)
{
refreshLayout.refreshFinish(PullToRefreshLayout.REFRESH_FAIL);
}
}.sendEmptyMessageDelayed(0, 5000);
}
}
实现OnRefreshListener接口，重写onRefresh方法即可，再次强调这不是我写的代码，优快云原文地址：
http://blog.youkuaiyun.com/zhongkejingwang/article/details/38340701，不要说我侵权了。
好了，其实在大部分项目里的下拉刷新都用到了类似上面的逻辑，接下来我们来看下Google官方提供的SwipeRefreshLayout，这个用起来更上面是一样的，非常简单，看布局：
<?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:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v4.widget.SwipeRefreshLayout
android:id="@+id/my_swipe"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ListView
android:id="@+id/myListView"
android:layout_width="match_parent"
android:layout_height="match_parent" >
</ListView>
</android.support.v4.widget.SwipeRefreshLayout>
</RelativeLayout>
也是嵌套在ListView的外面，用起来也跟刚才一样：
package com.fq.swiperefreshlayout;
import android.os.Handler;
import android.os.Message;
import android.support.v4.widget.SwipeRefreshLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class MainActivity extends AppCompatActivity implements SwipeRefreshLayout.OnRefreshListener {
private static final int REFRESH_COMPLETE = 0X110;
private SwipeRefreshLayout mSwipeLayout;
private ListView mListView;
private ArrayAdapter<String> mAdapter;
private List<String> mDatas = new ArrayList<String>(Arrays.asList("item1", "item2", "item3"));
public android.os.Handler mHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what)
{
case REFRESH_COMPLETE:
mDatas.addAll(Arrays.asList("item4", "item5", "item6"));
mAdapter.notifyDataSetChanged();
mSwipeLayout.setRefreshing(false);
break;
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mListView = (ListView) findViewById(R.id.myListView);
mSwipeLayout = (SwipeRefreshLayout) findViewById(R.id.my_swipe);
mSwipeLayout.setOnRefreshListener(this);
mAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, mDatas);
mListView.setAdapter(mAdapter);
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
}
public void onRefresh()
{
mHandler.sendEmptyMessageDelayed(REFRESH_COMPLETE, 2000);
}
}
下面是执行效果：
当下用到android下拉刷新的应用还是非常多的，可以自己按照第一种方式的思路完善下，也可以直接用官网的SwipeRefreshLayout ，如有问题，欢迎指正，谢谢。
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