前言

前面在介绍控件TabLayout控件和CoordinatorLayout使用的时候说了下实现京东、天猫详情页面的效果，今天要说的是优化版，是我们线上实现的效果，首先看一下效果：

项目结构分析

首先我们来分析一下要实现上面的效果，我们需要怎么做。顶部是一个可以滑动切换Tab，可以用ViewPager+Fragment实现，也可以使用系统的TabLayout控件实现；而下面的 View是一个可以滑动拖动效果的View，可以采用网上一个叫做DragLayout的控件，我这里是自己实现了一个，主要是通过对View的事件分发的一些处理；然后滑动到下面就是一个图文详情的View（Fragment），本页面包含两个界面：详情页面和参数页面；最后是评价的View（Fragment）。经过上面的分析，我们的界面至少需要4个Fragement，首先来看一下项目结构：

代码讲解

代码比较多，这里只讲解几个核心的方法类。首先我们来看一下我们自己是的这个具有阻尼效果的View，我们知道要实现的效果，我们需要对View的事件做一个全面的实现。这里首先说一下View的事件分发的流程：onInterceptTouchEvent()–>dispatchTouchEvent()–>onTouchEvent();
首先我们需要对View传过来的事件做一个拦截：

ensureTarget(); 
        if (null == mTarget) { 
            return false; 
        } 
        if (!isEnabled()) { 
            return false; 
        } 
        final int aciton = MotionEventCompat.getActionMasked(ev); 
        boolean shouldIntercept = false; 
        switch (aciton) { 
            case MotionEvent.ACTION_DOWN: { 
                mInitMotionX = ev.getX(); 
                mInitMotionY = ev.getY(); 
                shouldIntercept = false; 
                break; 
            } 
            case MotionEvent.ACTION_MOVE: { 
                final float x = ev.getX(); 
                final float y = ev.getY(); 
 
                final float xDiff = x - mInitMotionX; 
                final float yDiff = y - mInitMotionY; 
 
                if (canChildScrollVertically((int) yDiff)) { 
                    shouldIntercept = false; 
                } else { 
                    final float xDiffabs = Math.abs(xDiff); 
                    final float yDiffabs = Math.abs(yDiff); 
 
                    if (yDiffabs > mTouchSlop && yDiffabs >= xDiffabs 
                            && !(mStatus == Status.CLOSE && yDiff > 0 
                            || mStatus == Status.OPEN && yDiff < 0)) { 
                        shouldIntercept = true; 
                    } 
                } 
                break; 
            } 
            case MotionEvent.ACTION_UP: 
            case MotionEvent.ACTION_CANCEL: { 
                shouldIntercept = false; 
                break; 
            } 
        } 
        return shouldIntercept;

最后转发给onTouchEvent

ensureTarget(); 
        if (null == mTarget) { 
            return false; 
        } 
        if (!isEnabled()) { 
            return false; 
        } 
        boolean wantTouch = true; 
        final int action = MotionEventCompat.getActionMasked(ev); 
        switch (action) { 
            case MotionEvent.ACTION_DOWN: { 
                if (mTarget instanceof View) { 
                    wantTouch = true; 
                } 
                break; 
            } 
 
            case MotionEvent.ACTION_MOVE: { 
                final float y = ev.getY(); 
                final float yDiff = y - mInitMotionY; 
                if (canChildScrollVertically(((int) yDiff))) { 
                    wantTouch = false; 
                } else { 
                    processTouchEvent(yDiff); 
                    wantTouch = true; 
                } 
                break; 
            } 
            case MotionEvent.ACTION_UP: 
            case MotionEvent.ACTION_CANCEL: { 
                finishTouchEvent(); 
                wantTouch = false; 
                break; 
            } 
        } 
        return wantTouch;

滑动事件完了之后我们需要调用request方法对View做一个重绘：

final int left = l; 
        final int right = r; 
        int top; 
        int bottom; 
        final int offset = (int) mSlideOffset; 
        View child; 
        for (int i = 0; i < getChildCount(); i++) { 
            child = getChildAt(i); 
            if (child.getVisibility() == GONE) { 
                continue; 
            } 
            if (child == mBehindView) { 
                top = b + offset; 
                bottom = top + b - t; 
            } else { 
                top = t + offset; 
                bottom = b + offset; 
            } 
            child.layout(left, top, right, bottom); 
        }

上下滑动也是涉及到两个界面：mFrontView和mBehindView，然后通过判断滑动事件来显示哪一个View。具体看代码：

package com.xzh.gooddetail.view; 
import android.animation.Animator; 
import android.animation.AnimatorListenerAdapter; 
import android.animation.ValueAnimator; 
import android.content.Context; 
import android.content.res.TypedArray; 
import android.os.Parcel; 
import android.os.Parcelable; 
import android.support.v4.view.MotionEventCompat; 
import android.support.v4.view.ViewCompat; 
import android.util.AttributeSet; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.ViewConfiguration; 
import android.view.ViewGroup; 
import android.widget.AbsListView; 
import android.widget.FrameLayout; 
import android.widget.LinearLayout; 
import android.widget.RelativeLayout; 
import com.xzh.gooddetail.R; 
public class SlideDetailsLayout extends ViewGroup { 
public interface OnSlideDetailsListener { 
void onStatusChanged(Status status); 
} 
public enum Status { 
CLOSE, 
OPEN; 
public static Status valueOf(int stats) { 
if (0 == stats) { 
return CLOSE; 
} else if (1 == stats) { 
return OPEN; 
} else { 
return CLOSE; 
} 
} 
} 
private static final float DEFAULT_PERCENT = 0.2f; 
private static final int DEFAULT_DURATION = 300; 
private View mFrontView; 
private View mBehindView; 
private float mTouchSlop; 
private float mInitMotionY; 
private float mInitMotionX; 
private View mTarget; 
private float mSlideOffset; 
private Status mStatus = Status.CLOSE; 
private boolean isFirstShowBehindView = true; 
private float mPercent = DEFAULT_PERCENT; 
private long mDuration = DEFAULT_DURATION; 
private int mDefaultPanel = 0; 
private OnSlideDetailsListener mOnSlideDetailsListener; 
public SlideDetailsLayout(Context context) { 
this(context, null); 
} 
public SlideDetailsLayout(Context context, AttributeSet attrs) { 
this(context, attrs, 0); 
} 
public SlideDetailsLayout(Context context, AttributeSet attrs, int defStyleAttr) { 
super(context, attrs, defStyleAttr); 
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.SlideDetailsLayout, defStyleAttr, 0); 
mPercent = a.getFloat(R.styleable.SlideDetailsLayout_percent, DEFAULT_PERCENT); 
mDuration = a.getInt(R.styleable.SlideDetailsLayout_duration, DEFAULT_DURATION); 
mDefaultPanel = a.getInt(R.styleable.SlideDetailsLayout_default_panel, 0); 
a.recycle(); 
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop(); 
} 
public void setOnSlideDetailsListener(OnSlideDetailsListener listener) { 
this.mOnSlideDetailsListener = listener; 
} 
public void smoothOpen(boolean smooth) { 
if (mStatus != Status.OPEN) { 
mStatus = Status.OPEN; 
final float height = -getMeasuredHeight(); 
animatorSwitch(0, height, true, smooth ? mDuration : 0); 
} 
} 
public void smoothClose(boolean smooth) { 
if (mStatus != Status.CLOSE) { 
mStatus = Status.CLOSE; 
final float height = -getMeasuredHeight(); 
animatorSwitch(height, 0, true, smooth ? mDuration : 0); 
} 
} 
@Override 
protected LayoutParams generateDefaultLayoutParams() { 
return new MarginLayoutParams(MarginLayoutParams.WRAP_CONTENT, MarginLayoutParams.WRAP_CONTENT); 
} 
@Override 
public LayoutParams generateLayoutParams(AttributeSet attrs) { 
return new MarginLayoutParams(getContext(), attrs); 
} 
@Override 
protected LayoutParams generateLayoutParams(LayoutParams p) { 
return new MarginLayoutParams(p); 
} 
@Override 
protected void onFinishInflate() { 
final int childCount = getChildCount(); 
if (1 >= childCount) { 
throw new RuntimeException("SlideDetailsLayout only accept childs more than 1!!"); 
} 
mFrontView = getChildAt(0); 
mBehindView = getChildAt(1); 
if (mDefaultPanel == 1) { 
post(new Runnable() { 
@Override 
public void run() { 
smoothOpen(false); 
} 
}); 
} 
} 
@Override 
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
final int pWidth = MeasureSpec.getSize(widthMeasureSpec); 
final int pHeight = MeasureSpec.getSize(heightMeasureSpec); 
final int childWidthMeasureSpec = 
MeasureSpec.makeMeasureSpec(pWidth, MeasureSpec.EXACTLY); 
final int childHeightMeasureSpec = 
MeasureSpec.makeMeasureSpec(pHeight, MeasureSpec.EXACTLY); 
View child; 
for (int i = 0; i < getChildCount(); i++) { 
child = getChildAt(i); 
if (child.getVisibility() == GONE) { 
continue; 
} 
measureChild(child, childWidthMeasureSpec, childHeightMeasureSpec); 
} 
setMeasuredDimension(pWidth, pHeight); 
} 
@Override 
protected void onLayout(boolean changed, int l, int t, int r, int b) { 
final int left = l; 
final int right = r; 
int top; 
int bottom; 
final int offset = (int) mSlideOffset; 
View child; 
for (int i = 0; i < getChildCount(); i++) { 
child = getChildAt(i); 
if (child.getVisibility() == GONE) { 
continue; 
} 
if (child == mBehindView) { 
top = b + offset; 
bottom = top + b - t; 
} else { 
top = t + offset; 
bottom = b + offset; 
} 
child.layout(left, top, right, bottom); 
} 
} 
@Override 
public boolean onInterceptTouchEvent(MotionEvent ev) { 
ensureTarget(); 
if (null == mTarget) { 
return false; 
} 
if (!isEnabled()) { 
return false; 
} 
final int aciton = MotionEventCompat.getActionMasked(ev); 
boolean shouldIntercept = false; 
switch (aciton) { 
case MotionEvent.ACTION_DOWN: { 
mInitMotionX = ev.getX(); 
mInitMotionY = ev.getY(); 
shouldIntercept = false; 
break; 
} 
case MotionEvent.ACTION_MOVE: { 
final float x = ev.getX(); 
final float y = ev.getY(); 
final float xDiff = x - mInitMotionX; 
final float yDiff = y - mInitMotionY; 
if (canChildScrollVertically((int) yDiff)) { 
shouldIntercept = false; 
} else { 
final float xDiffabs = Math.abs(xDiff); 
final float yDiffabs = Math.abs(yDiff); 
if (yDiffabs > mTouchSlop && yDiffabs >= xDiffabs 
&& !(mStatus == Status.CLOSE && yDiff > 0 
|| mStatus == Status.OPEN && yDiff < 0)) { 
shouldIntercept = true; 
} 
} 
break; 
} 
case MotionEvent.ACTION_UP: 
case MotionEvent.ACTION_CANCEL: { 
shouldIntercept = false; 
break; 
} 
} 
return shouldIntercept; 
} 
@Override 
public boolean onTouchEvent(MotionEvent ev) { 
ensureTarget(); 
if (null == mTarget) { 
return false; 
} 
if (!isEnabled()) { 
return false; 
} 
boolean wantTouch = true; 
final int action = MotionEventCompat.getActionMasked(ev); 
switch (action) { 
case MotionEvent.ACTION_DOWN: { 
if (mTarget instanceof View) { 
wantTouch = true; 
} 
break; 
} 
case MotionEvent.ACTION_MOVE: { 
final float y = ev.getY(); 
final float yDiff = y - mInitMotionY; 
if (canChildScrollVertically(((int) yDiff))) { 
wantTouch = false; 
} else { 
processTouchEvent(yDiff); 
wantTouch = true; 
} 
break; 
} 
case MotionEvent.ACTION_UP: 
case MotionEvent.ACTION_CANCEL: { 
finishTouchEvent(); 
wantTouch = false; 
break; 
} 
} 
return wantTouch; 
} 
private void processTouchEvent(final float offset) { 
if (Math.abs(offset) < mTouchSlop) { 
return; 
} 
final float oldOffset = mSlideOffset; 
if (mStatus == Status.CLOSE) { 
// reset if pull down 
if (offset >= 0) { 
mSlideOffset = 0; 
} else { 
mSlideOffset = offset; 
} 
if (mSlideOffset == oldOffset) { 
return; 
} 
} else if (mStatus == Status.OPEN) { 
final float pHeight = -getMeasuredHeight(); 
if (offset <= 0) { 
mSlideOffset = pHeight; 
} else { 
final float newOffset = pHeight + offset; 
mSlideOffset = newOffset; 
} 
if (mSlideOffset == oldOffset) { 
return; 
} 
} 
requestLayout(); 
} 
private void finishTouchEvent() { 
final int pHeight = getMeasuredHeight(); 
final int percent = (int) (pHeight * mPercent); 
final float offset = mSlideOffset; 
boolean changed = false; 
if (Status.CLOSE == mStatus) { 
if (offset <= -percent) { 
mSlideOffset = -pHeight; 
mStatus = Status.OPEN; 
changed = true; 
} else { 
mSlideOffset = 0; 
} 
} else if (Status.OPEN == mStatus) { 
if ((offset + pHeight) >= percent) { 
mSlideOffset = 0; 
mStatus = Status.CLOSE; 
changed = true; 
} else { 
mSlideOffset = -pHeight; 
} 
} 
animatorSwitch(offset, mSlideOffset, changed); 
} 
private void animatorSwitch(final float start, final float end) { 
animatorSwitch(start, end, true, mDuration); 
} 
private void animatorSwitch(final float start, final float end, final long duration) { 
animatorSwitch(start, end, true, duration); 
} 
private void animatorSwitch(final float start, final float end, final boolean changed) { 
animatorSwitch(start, end, changed, mDuration); 
} 
private void animatorSwitch(final float start, 
final float end, 
final boolean changed, 
final long duration) { 
ValueAnimator animator = ValueAnimator.ofFloat(start, end); 
animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() { 
@Override 
public void onAnimationUpdate(ValueAnimator animation) { 
mSlideOffset = (float) animation.getAnimatedValue(); 
requestLayout(); 
} 
}); 
animator.addListener(new AnimatorListenerAdapter() { 
@Override 
public void onAnimationEnd(Animator animation) { 
super.onAnimationEnd(animation); 
if (changed) { 
if (mStatus == Status.OPEN) { 
checkAndFirstOpenPanel(); 
} 
if (null != mOnSlideDetailsListener) { 
mOnSlideDetailsListener.onStatusChanged(mStatus); 
} 
} 
} 
}); 
animator.setDuration(duration); 
animator.start(); 
} 
private void checkAndFirstOpenPanel() { 
if (isFirstShowBehindView) { 
isFirstShowBehindView = false; 
mBehindView.setVisibility(VISIBLE); 
} 
} 
private void ensureTarget() { 
if (mStatus == Status.CLOSE) { 
mTarget = mFrontView; 
} else { 
mTarget = mBehindView; 
} 
} 
protected boolean canChildScrollVertically(int direction) { 
if (mTarget instanceof AbsListView) { 
return canListViewSroll((AbsListView) mTarget); 
} else if (mTarget instanceof FrameLayout || 
mTarget instanceof RelativeLayout || 
mTarget instanceof LinearLayout) { 
View child; 
for (int i = 0; i < ((ViewGroup) mTarget).getChildCount(); i++) { 
child = ((ViewGroup) mTarget).getChildAt(i); 
if (child instanceof AbsListView) { 
return canListViewSroll((AbsListView) child); 
} 
} 
} 
if (android.os.Build.VERSION.SDK_INT < 14) { 
return ViewCompat.canScrollVertically(mTarget, -direction) || mTarget.getScrollY() > 0; 
} else { 
return ViewCompat.canScrollVertically(mTarget, -direction); 
} 
} 
protected boolean canListViewSroll(AbsListView absListView) { 
if (mStatus == Status.OPEN) { 
return absListView.getChildCount() > 0 
&& (absListView.getFirstVisiblePosition() > 0 || absListView.getChildAt(0) 
.getTop() < 
absListView.getPaddingTop()); 
} else { 
final int count = absListView.getChildCount(); 
return count > 0 
&& (absListView.getLastVisiblePosition() < count - 1 
|| absListView.getChildAt(count - 1) 
.getBottom() > absListView.getMeasuredHeight()); 
} 
} 
@Override 
protected Parcelable onSaveInstanceState() { 
SavedState ss = new SavedState(super.onSaveInstanceState()); 
ss.offset = mSlideOffset; 
ss.status = mStatus.ordinal(); 
return ss; 
} 
@Override 
protected void onRestoreInstanceState(Parcelable state) { 
SavedState ss = (SavedState) state; 
super.onRestoreInstanceState(ss.getSuperState()); 
mSlideOffset = ss.offset; 
mStatus = Status.valueOf(ss.status); 
if (mStatus == Status.OPEN) { 
mBehindView.setVisibility(VISIBLE); 
} 
requestLayout(); 
} 
static class SavedState extends BaseSavedState { 
private float offset; 
private int status; 
public SavedState(Parcel source) { 
super(source); 
offset = source.readFloat(); 
status = source.readInt(); 
} 
public SavedState(Parcelable superState) { 
super(superState); 
} 
@Override 
public void writeToParcel(Parcel out, int flags) { 
super.writeToParcel(out, flags); 
out.writeFloat(offset); 
out.writeInt(status); 
} 
public static final Creator<SavedState> CREATOR = 
new Creator<SavedState>() { 
public SavedState createFromParcel(Parcel in) { 
return new SavedState(in); 
} 
public SavedState[] newArray(int size) { 
return new SavedState[size]; 
} 
}; 
} 
} 

接下来就是一些Fragment等的页面填充，也没啥好讲的，代码又很多可以优化的地方，在优化的地方，笔者也列出了优化的方案，大家可以根据自己的实际情况做页面级的优化。
附：Android仿京东、天猫商品详情页源码