一、淘寶商品詳情頁效果
先看一下淘寶詳情頁的效果
我們的效果
二、實作思路
使用兩個scrollView,兩個scrollView 豎直排列,通過自定義viewGroup來控制兩個scrollView的豎直排列,以及滑動事件的處理。如下圖
三、具體實作
1、繼承viewGroup自定義布局View 重寫onMeasure()和onLayout方法,在onLayout方法中完成對兩個子ScrollView的豎直排列布局,代碼如下: 布局檔案:
<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"
tools:context="com.baoyunlong.view.pulluptoloadmore.MainActivity">
<com.baoyunlong.view.pulluptoloadmore.PullUpToLoadMore
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.baoyunlong.view.pulluptoloadmore.MyScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:scaleType="fitXY"
android:src="@drawable/a1"
android:layout_width="match_parent"
android:layout_height="180dp" />
<TextView
android:text="這裡是标題"
android:textSize="18dp"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:layout_marginTop="10dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<TextView
android:layout_marginTop="10dp"
android:text="子标題"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:textSize="18dp"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
..............
<LinearLayout
android:layout_height="0dp"
android:layout_weight="1"
android:gravity="bottom"
android:layout_width="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:height="50dp"
android:background="#b11"
android:gravity="center"
android:text="繼續拖動檢視圖文詳情"
android:textColor="#000" />
</LinearLayout>
</LinearLayout>
</com.baoyunlong.view.pulluptoloadmore.MyScrollView>
<com.baoyunlong.view.pulluptoloadmore.MyScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/a1" />
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/a3" />
.........
</LinearLayout>
</com.baoyunlong.view.pulluptoloadmore.MyScrollView>
</com.baoyunlong.view.pulluptoloadmore.PullUpToLoadMore>
</RelativeLayout>
代碼:
public class PullUpToLoadMore extends ViewGroup {
public PullUpToLoadMore(Context context) {
super(context);
}
public PullUpToLoadMore(Context context, AttributeSet attrs) {
super(context, attrs);
}
public PullUpToLoadMore(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
measureChildren(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childCount = getChildCount();
int childTop = t;
for (int i = 0; i < childCount; i++) {
View child = getChildAt(i);
child.layout(l, childTop, r, childTop + child.getMeasuredHeight());
childTop += child.getMeasuredHeight();
}
}
}
2、處理滑動事件 規則如下 : (1)、當處于第一屏時 第一個ScrollView已經滑動到底部并且滑動方向是往上滑動,這個時候滑動事件應該交給父view處理也就是攔截事件讓onInterceptTouchEvent傳回true.然後父view通過scrollBy()方法滾動,顯示出第二個scrollView。 (2)、當處于第二屏時 第二個ScrollView已經滑動到頂部并且滑動方向是往下滑動,這個時候滑動事件交給父view處理,根據滑動事件顯示出第一個ScrollView。 (3)、當手指離開螢幕時,根據滑動速度來決定是回彈到第一個ScrollView還是第二個ScrollView,通過VelocityTracker來擷取滑動速度。 3、一些細節的處理 (1)、如果仔細看觀察淘寶的實作效果你會發現,當你滑動到剛剛看到 “繼續拖動,檢視圖文詳情”的時候,手指擡起,然後再按下重新向上拖動你會發現,第二頁并不會劃出來,而是停留在了“繼續拖動,檢視圖文詳情”的底部,京東的效果也是一樣。這樣使用者體驗不太好,我們來優化一下。其實通過檢視ScrollView的源碼可以看出來,這是因為ScrollView類的onTouchEvent方法的預設實作,調用了parent.requestDisallowInterceptTouchEvent(true)方法 阻止了我們攔截事件,導緻我們父view的onInterceptTouchEvent方法無法執行,也就攔截不到事件,攔截不到事件我們的onTouchEvent就無法執行,onTouchEvent無法執行,我們寫在onTouchEvent裡面的滾動邏輯就執行不到了,導緻了上面我們看到的劃不動的效果。解決方法就是,我們需要重寫dispatchTouchEvent()方法,防止子view幹擾我們,這樣我們滑動的時候就可以一氣呵成了。代碼如下:
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//防止子View禁止父view攔截事件
this.requestDisallowInterceptTouchEvent(false);
return super.dispatchTouchEvent(ev);
}
(2)、監聽ScrollView滑動事件的問題
ScrollView沒有提供滾動事件的監聽方法,也就沒法判斷是否滾動到了頂部,或者底部,這裡我們繼承ScrollView 自己實作滾動事件監聽。
/**
* Created by baoyunlong on 16/6/8.
*/
public class MyScrollView extends ScrollView {
private static String TAG=MyScrollView.class.getName();
public void setScrollListener(ScrollListener scrollListener) {
this.mScrollListener = scrollListener;
}
private ScrollListener mScrollListener;
public MyScrollView(Context context) {
super(context);
}
public MyScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
switch (ev.getAction()){
case MotionEvent.ACTION_MOVE:
if(mScrollListener!=null){
int contentHeight=getChildAt(0).getHeight();
int scrollHeight=getHeight();
int scrollY=getScrollY();
mScrollListener.onScroll(scrollY);
if(scrollY+scrollHeight>=contentHeight||contentHeight<=scrollHeight){
mScrollListener.onScrollToBottom();
}else {
mScrollListener.notBottom();
}
if(scrollY==0){
mScrollListener.onScrollToTop();
}
}
break;
}
boolean result=super.onTouchEvent(ev);
requestDisallowInterceptTouchEvent(false);
return result;
}
public interface ScrollListener{
void onScrollToBottom();
void onScrollToTop();
void onScroll(int scrollY);
void notBottom();
}
4、完整代碼如下
/**
* Created by baoyunlong on 16/6/8.
*/
public class PullUpToLoadMore extends ViewGroup {
public static String TAG = PullUpToLoadMore.class.getName();
MyScrollView topScrollView, bottomScrollView;
VelocityTracker velocityTracker = VelocityTracker.obtain();
Scroller scroller = new Scroller(getContext());
int currPosition = 0;
int position1Y;
int lastY;
public int scaledTouchSlop;//最小滑動距離
int speed = 200;
boolean isIntercept;
public boolean bottomScrollVIewIsInTop = false;
public boolean topScrollViewIsBottom = false;
public PullUpToLoadMore(Context context) {
super(context);
init();
}
public PullUpToLoadMore(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public PullUpToLoadMore(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
private void init() {
post(new Runnable() {
@Override
public void run() {
topScrollView = (MyScrollView) getChildAt(0);
bottomScrollView = (MyScrollView) getChildAt(1);
topScrollView.setScrollListener(new MyScrollView.ScrollListener() {
@Override
public void onScrollToBottom() {
topScrollViewIsBottom = true;
}
@Override
public void onScrollToTop() {
}
@Override
public void onScroll(int scrollY) {
}
@Override
public void notBottom() {
topScrollViewIsBottom = false;
}
});
bottomScrollView.setScrollListener(new MyScrollView.ScrollListener() {
@Override
public void onScrollToBottom() {
}
@Override
public void onScrollToTop() {
}
@Override
public void onScroll(int scrollY) {
if (scrollY == 0) {
bottomScrollVIewIsInTop = true;
} else {
bottomScrollVIewIsInTop = false;
}
}
@Override
public void notBottom() {
}
});
position1Y = topScrollView.getBottom();
scaledTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
}
});
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
//防止子View禁止父view攔截事件
this.requestDisallowInterceptTouchEvent(false);
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
int y = (int) ev.getY();
switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
lastY = y;
break;
case MotionEvent.ACTION_MOVE:
//判斷是否已經滾動到了底部
if (topScrollViewIsBottom) {
int dy = lastY - y;
//判斷是否是向上滑動和是否在第一屏
if (dy > 0 && currPosition == 0) {
if (dy >= scaledTouchSlop) {
isIntercept = true;//攔截事件
lastY=y;
}
}
}
if (bottomScrollVIewIsInTop) {
int dy = lastY - y;
//判斷是否是向下滑動和是否在第二屏
if (dy < 0 && currPosition == 1) {
if (Math.abs(dy) >= scaledTouchSlop) {
isIntercept = true;
}
}
}
break;
}
return isIntercept;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int y = (int) event.getY();
velocityTracker.addMovement(event);
switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:
int dy = lastY - y;
if (getScrollY() + dy < 0) {
dy = getScrollY() + dy + Math.abs(getScrollY() + dy);
}
if (getScrollY() + dy + getHeight() > bottomScrollView.getBottom()) {
dy = dy - (getScrollY() + dy - (bottomScrollView.getBottom() - getHeight()));
}
scrollBy(0, dy);
break;
case MotionEvent.ACTION_UP:
isIntercept = false;
velocityTracker.computeCurrentVelocity(1000);
float yVelocity = velocityTracker.getYVelocity();
if (currPosition == 0) {
if (yVelocity < 0 && yVelocity < -speed) {
smoothScroll(position1Y);
currPosition = 1;
} else {
smoothScroll(0);
}
} else {
if (yVelocity > 0 && yVelocity > speed) {
smoothScroll(0);
currPosition = 0;
} else {
smoothScroll(position1Y);
}
}
break;
}
lastY = y;
return true;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
measureChildren(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int childCount = getChildCount();
int childTop = t;
for (int i = 0; i < childCount; i++) {
View child = getChildAt(i);
child.layout(l, childTop, r, childTop + child.getMeasuredHeight());
childTop += child.getMeasuredHeight();
}
}
//通過Scroller實作彈性滑動
private void smoothScroll(int tartY) {
int dy = tartY - getScrollY();
scroller.startScroll(getScrollX(), getScrollY(), 0, dy);
invalidate();
}
@Override
public void computeScroll() {
if (scroller.computeScrollOffset()) {
scrollTo(scroller.getCurrX(), scroller.getCurrY());
postInvalidate();
}
}
}
四、源碼
github位址