淘宝上拉查看图文详情效果
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一、需要注意的地方是：
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1、如果是手动滑到底部需要再次按下才能继续往下滑，自动滚动到底部则不需要
2、在由上一个ScrollView滑动到下一个ScrollView的过程中多只手指相继拖动也不会导致布局的剧变，也就是多个pointer的滑动不会导致move距离的剧变。
这个Layout的实现思路是：
在布局中放置两个ScrollView，并为其设置OnTouchListener，时刻判断ScrollView的滚动距离，一旦第一个ScrollView滚动到底部，则标识改为可向上拖动，此时开始记录滑动距离mMoveLen，根据mMoveLen重新layout两个ScrollView；同理，监听第二个ScrollView是否滚动到顶部，以往下拖动。
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二、涉及到的知识点小结：
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1、Timer和TimerTask
Timer是一种定时器工具，用来在一个后台线程计划执行指定任务。它可以计划执行一个任务一次或反复多次。
TimerTask一个抽象类，它的子类代表一个可以被Timer计划的任务。
2、VelocityTracker
VelocityTracker顾名思义即速度跟踪，在Android中主要应用于touch event， VelocityTracker通过跟踪一连串事件实时计算出当前的速度，这样的用法在android系统空间中随处可见，比如Gestures中的Fling, Scrolling等。
3、handler.obtainMessage().sendToTarget()
使用的是sendToTarget()而不是sendMessage(),sendToTarget()方法并不是真正的将Message发送出去，而是将Message压入了MessageQueue中，真正去回调handleMessage还是在Looper.loop()中完成的。
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三、核心代码
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1、自定义ScrollView类
package com.trthi.mall.components;
import java.util.Timer;
import java.util.TimerTask;
import android.content.Context;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.widget.RelativeLayout;
import android.widget.ScrollView;
import com.trthi.mall.listeners.ScrollChangedListener;
/**
* 包含两个ScrollView的容器
*
*
*/
public class ScrollViewContainer extends RelativeLayout {
/**
* 自动上滑
*/
public static final int AUTO_UP = 0;
/**
* 自动下滑
*/
public static final int AUTO_DOWN = 1;
/**
* 动画完成
*/
public static final int DONE = 2;
/**
* 动画速度
*/
public static final float SPEED = 8f;
private boolean isMeasured = false;
/**
* 用于计算手滑动的速度
*/
private VelocityTracker vt;
private int mViewHeight;
private int mViewWidth;
private View topView;
private View bottomView;
private boolean canPullDown;
private boolean canPullUp;
private int state = DONE;
/**
* 记录当前展示的是哪个view，0是topView，1是bottomView
*/
private int mCurrentViewIndex = 0;
public int getmCurrentViewIndex(){
return mCurrentViewIndex;
}
/**
* 手滑动距离，这个是控制布局的主要变量
*/
private float mMoveLen;
private MyTimer mTimer;
private float mLastY;
/**
* 用于控制是否变动布局的另一个条件，mEvents==0时布局可以变动
*/
private int mEvents;
private ScrollChangedListener scrollChangedListener = null;
public void setScrollChangedListener(ScrollChangedListener scrollChangedListener){
this.scrollChangedListener = scrollChangedListener;
}
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (mMoveLen != 0) {
if (state == AUTO_UP) {
mMoveLen -= SPEED;
if (mMoveLen <= -mViewHeight) {
mMoveLen = -mViewHeight;
state = DONE;
mCurrentViewIndex = 1;
if (scrollChangedListener != null) {
scrollChangedListener.onScrollChanged(mCurrentViewIndex);
}
}
} else if (state == AUTO_DOWN) {
mMoveLen += SPEED;
if (mMoveLen >= 0) {
mMoveLen = 0;
state = DONE;
mCurrentViewIndex = 0;
if (scrollChangedListener != null) {
scrollChangedListener.onScrollChanged(mCurrentViewIndex);
}
}
} else {
mTimer.cancel();
}
}
requestLayout();
}
};
public ScrollViewContainer(Context context) {
this(context,null);
}
public ScrollViewContainer(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public ScrollViewContainer(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
mTimer = new MyTimer(handler);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
switch (ev.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
try {
if (vt == null)
vt = VelocityTracker.obtain();
else
vt.clear();
} catch (Exception e) {
e.printStackTrace();
}
mLastY = ev.getY();
vt.addMovement(ev);
mEvents = 0;
break;
case MotionEvent.ACTION_POINTER_DOWN:
case MotionEvent.ACTION_POINTER_UP:
// 多一只手指按下或抬起时舍弃将要到来的第一个事件move，防止多点拖拽的bug
mEvents = -1;
break;
case MotionEvent.ACTION_MOVE:
vt.addMovement(ev);
if (canPullUp && mCurrentViewIndex == 0 && mEvents == 0) {
mMoveLen += (ev.getY() - mLastY);
// 防止上下越界
if (mMoveLen > 0) {
mMoveLen = 0;
mCurrentViewIndex = 0;
} else if (mMoveLen < -mViewHeight) {
mMoveLen = -mViewHeight;
mCurrentViewIndex = 1;
}
if (mMoveLen < -8) {
// 防止事件冲突
ev.setAction(MotionEvent.ACTION_CANCEL);
}
} else if (canPullDown && mCurrentViewIndex == 1 && mEvents == 0) {
mMoveLen += (ev.getY() - mLastY);
// 防止上下越界
if (mMoveLen < -mViewHeight) {
mMoveLen = -mViewHeight;
mCurrentViewIndex = 1;
} else if (mMoveLen > 0) {
mMoveLen = 0;
mCurrentViewIndex = 0;
}
if (mMoveLen > 8 - mViewHeight) {
// 防止事件冲突
ev.setAction(MotionEvent.ACTION_CANCEL);
}
} else
mEvents++;
mLastY = ev.getY();
requestLayout();
break;
case MotionEvent.ACTION_UP:
mLastY = ev.getY();
vt.addMovement(ev);
vt.computeCurrentVelocity(700);
// 获取Y方向的速度
float mYV = vt.getYVelocity();
if (mMoveLen == 0 || mMoveLen == -mViewHeight)
break;
if (Math.abs(mYV) < 500) {
// 速度小于一定值的时候当作静止释放，这时候两个View往哪移动取决于滑动的距离
if (mMoveLen <= -mViewHeight / 2) {
state = AUTO_UP;
} else if (mMoveLen > -mViewHeight / 2) {
state = AUTO_DOWN;
}
} else {
// 抬起手指时速度方向决定两个View往哪移动
if (mYV < 0)
state = AUTO_UP;
else
state = AUTO_DOWN;
}
mTimer.schedule(2);
break;
}
super.dispatchTouchEvent(ev);
return true;
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (!isMeasured) {
isMeasured = true;
mViewHeight = getMeasuredHeight();
mViewWidth = getMeasuredWidth();
topView = getChildAt(0);
bottomView = getChildAt(1);
bottomView.setOnTouchListener(bottomViewTouchListener);
topView.setOnTouchListener(topViewTouchListener);
}
topView.layout(0, (int) mMoveLen, mViewWidth,
topView.getMeasuredHeight() + (int) mMoveLen);
bottomView.layout(0, topView.getMeasuredHeight() + (int) mMoveLen,
mViewWidth, topView.getMeasuredHeight() + (int) mMoveLen
+ bottomView.getMeasuredHeight());
}
private OnTouchListener topViewTouchListener = new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
ScrollView sv = (ScrollView) v;
if (sv.getScrollY() == (sv.getChildAt(0).getMeasuredHeight() - sv
.getMeasuredHeight()) && mCurrentViewIndex == 0)
canPullUp = true;
else
canPullUp = false;
return false;
}
};
private OnTouchListener bottomViewTouchListener = new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
ScrollView sv = (ScrollView) v;
if (sv.getScrollY() == 0 && mCurrentViewIndex == 1)
canPullDown = true;
else
canPullDown = false;
return false;
}
};
class MyTimer {
private Handler handler;
private Timer timer;
private MyTask mTask;
public MyTimer(Handler handler) {
this.handler = handler;
timer = new Timer();
}
public void schedule(long period) {
if (mTask != null) {
mTask.cancel();
mTask = null;
}
mTask = new MyTask(handler);
timer.schedule(mTask, 0, period);
}
public void cancel() {
if (mTask != null) {
mTask.cancel();
mTask = null;
}
}
class MyTask extends TimerTask {
private Handler handler;
public MyTask(Handler handler) {
this.handler = handler;
}
@Override
public void run() {
handler.obtainMessage().sendToTarget();
}
}
}
}2、XML文件
<com.trthi.mall.components.ScrollViewContainer xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/scrollview"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.trthi.mall.fragments.ProductDetailFragment">
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="上拉显示图文详情"
android:textSize="16sp" />
LinearLayout>
ScrollView>
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<WebView
android:id="@+id/webView"
android:layout_width="match_parent"
android:layout_height="match_parent">
WebView>
LinearLayout>
ScrollView>
com.trthi.mall.components.ScrollViewContainer>
在activity中直接用setViewContent(R.layout.~)就可以显示效果
3、扩展：
根据需求，滑到底部有一个提示条，就像TextView一样，显示上拉显示图文详情之类的。但是当滑到下半部分时，在要向上滑显示的文字因该变为下拉显示商品详情之类的。这时就要利用到接口回调。
1）定义接口
public interface ScrollChangedListener {
//mCurrentViewIndex 表示当前是上半部分还是下半部分
void onScrollChanged(int mCurrentViewIndex);
}2）在自定义的ScrollView中设置回调的方法
private ScrollChangedListener scrollChangedListener = null;
public void setScrollChangedListener(ScrollChangedListener scrollChangedListener){
this.scrollChangedListener = scrollChangedListener;
}
以及在handler处的使用：
if (scrollChangedListener != null) {
scrollChangedListener.onScrollChanged(mCurrentViewIndex);
}3）在activity中要实现接口（即implements ScrollChangedListener ），然后重写抽象方法
@Override
public void onScrollChanged(int state) {
if(state == 0){
//TODO 修改textview的文字及图片方向
((TextView)mGoToPicView.getChildAt(1)).setText("上拉查看图文详情");
}else {
((TextView)mGoToPicView.getChildAt(1)).setText("下滑查看商品详情");
}
}一定不要忘了设置监听，
mScrollView = (ScrollViewContainer) findViewById(R.id.scrollview);
mScrollView.setScrollChangedListener(this);