NestedScrollingParent 实现复杂交互效果

最终效果:
上下排列 3 个 view, 依次为 RecyclerView ,NestedScrollView,RecyclerView,规则:子 View 可以滚动时 Touch 事件给子 view 消费,否则给父布局。

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1. 接口

NestedScrollingParent 用来配置子视图( NestedScrollingChild )嵌套滚动。

NestedScrollingParent 简称 NP
NestedScrollingChild 简称 NC

  1. NC 产生一个 touch 事件,调用 startNestedScroll,表示开始分享出去 touch 事件, NP 的 onStartNestedScroll 判断是否需要跟 NC 配合,返回 true 表示接受
  2. NC 调用 dispatchNestedPreScroll ,通知 NP 将要进行一个 Touch 事件,如移动 5个像素,NP 的 onNestedPreScroll 中收到通知,知道 NC 要准备移动5个像素,这时候 NP 正好也需要滑动 2 个像素,然后在 onNestedPreScroll 的参数 consumed[] 数组对应的方向(下标为0的x轴,下标为1的y轴)赋值 2,表示消费 2 个像素
  3. NC 拿到 consumed[] 数组,知道 NP 消费了 2 个像素,剩下了 3 个像素,然后自己根据需要再移动 3 个像素的距离,如果这时候 NC 由于某个原因只移动了 2 个像素,那么剩下的 1 个像素距离会调用 dispatchNestedScroll 给 NP,NP 在 onNestedScroll 处理剩下的未消费的 1 像素。最后,NC 调用 stopNestedScroll ,最后 NP 调用 onStopNestedScroll结束。

  4. 同 NestedScroll 类似的还有一套 NestedFling 操作,整体流程类似,NC 快速滑动产生一个 fling 事件,处理流程 NC.dispatchNestedPreFling -> NP.onNestedPreFling -> NC.dispatchNestedFling -> NP.onNestedFling

为什么 NC 和 NP 能相互配合滚动? 主要的源码在 NestedScrollingChildHelperNestedScrollingParentHelper

效果实现

自定 ViewGroup ,实现 NestedScrollingParent 接口,一个 NestedScrollingParentHelper 成员变量作为辅助

布局

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<?xml version="1.0" encoding="utf-8"?>
<xyz.hanks.nestedwebview.nestedscroll.NScrollView
xmlns:android="https://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView0"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#20f0"
android:scrollbarSize="3dp"
android:scrollbars="vertical"/>
<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="wrap_content">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#e1e1e1"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="100dp"
android:text="cdsadadlick"/>
<Button
android:layout_width="match_parent"
android:layout_height="100dp"
android:text="asddasda"/>
<TextView
android:layout_width="match_parent"
android:layout_height="100dp"
android:text="asdadarewe"/>
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#2f00"
android:scrollbarStyle="insideInset"
android:scrollbars="vertical"/>
</xyz.hanks.nestedwebview.nestedscroll.NScrollView>

基础的 onMeasure ,onLayout

onLayout

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/**
* NestedScrollView
* Created by hanks on 16/8/22.
*/
public class NScrollView extends ViewGroup implements NestedScrollingParent {
private static final String TAG = "NScrollView";
private int maxDistance = 0;
private int totalHeight = 0;
private NestedScrollingParentHelper mParentHelper;
private List<View> nestedScrollingChildList = new ArrayList<>();
private ScrollerCompat scroller;
public NScrollView(Context context) {
this(context, null);
}
public NScrollView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public NScrollView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
setOverScrollMode(View.OVER_SCROLL_NEVER);
mParentHelper = new NestedScrollingParentHelper(this);
scroller = ScrollerCompat.create(context);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
int parentHeight = getMeasuredHeight();
int top = t;
int lastChildHeight = 0;
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
LayoutParams layoutParams = child.getLayoutParams();
if (layoutParams.height == LayoutParams.MATCH_PARENT) {
layoutParams.height = parentHeight;
} else {
int childMeasuredHeight = child.getMeasuredHeight();
layoutParams.height = childMeasuredHeight;
}
log(child + "," + layoutParams.height);
child.setLayoutParams(layoutParams);
child.layout(l, top, r, top + layoutParams.height);
top += layoutParams.height;
lastChildHeight = layoutParams.height;
}
maxDistance = top - lastChildHeight;
totalHeight = top;
//viewGroup.layout(l, t, r, top);
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
nestedScrollingChildList.clear();
for (int i = 0; i < getChildCount(); i++) {
View child = getChildAt(i);
nestedScrollingChildList.add(child);
}
}
private void consumeEvent(int dx, int dy, int[] consumed) {
scrollBy(dx, dy);
consumed[0] = 0;
consumed[1] = dy;
log("parent consumed pre : " + consumed[1]);
}
public int getCurrentWrapline(View target) {
int line = 0;
for (View view : nestedScrollingChildList) {
if (view == target) {
return line;
}
line += view.getHeight();
}
return line;
}
@Override
public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
return (nestedScrollAxes & SCROLL_AXIS_VERTICAL) != 0;
}
@Override
public void onNestedScrollAccepted(View child, View target, int axes) {
mParentHelper.onNestedScrollAccepted(child, target, axes);
return;
}
@Override
public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) {
logi("======== onStartNestedScroll =======");
int scrollY = getScrollY();
int line = getCurrentWrapline(target);
boolean targetScrollDown = ScrollUtils.canChildScrollDown(target);
boolean targetScrollUp = ScrollUtils.canChildScrollUp(target);
log("onNestedPreScroll: target = [" + target.getClass().getName() + "], dx = [" + dx + "], dy = [" + dy + "], consumed = [" + consumed + "]");
log("scrollY:" + scrollY + ",lien:" + line + ",scrollDown:" + targetScrollDown + "scrollUp:" + targetScrollUp + ",maxDistance" + maxDistance);
if (scrollY == line
&& ((dy > 0 && targetScrollDown) || (dy < 0 && targetScrollUp))) {
return;
}
if (scrollY + dy < 0 || scrollY + dy > maxDistance) {
return;
}
consumeEvent(0, dy, consumed);
}
@Override
public void onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
int scrollY = getScrollY();
if (scrollY + dyUnconsumed < 0 || scrollY + dyUnconsumed > maxDistance) {
return;
}
scrollBy(dxUnconsumed, dyUnconsumed);
log("onNestedScroll: target = [" + target.getClass().getName() + "], dxConsumed = [" + dxConsumed + "], dyConsumed = [" + dyConsumed + "], dxUnconsumed = [" + dxUnconsumed + "], dyUnconsumed = [" + dyUnconsumed + "]");
}
@Override
public boolean onNestedPreFling(View target, float velocityX, float velocityY) {
int scrollY = getScrollY();
log("onNestedPreFling: target = [" + target.getClass().getName() + "], velocityX = [" + velocityX + "], velocityY = [" + velocityY + "]" + ",scrollY:" + scrollY);
int line = getCurrentWrapline(target);
if (scrollY != line) {
fling((int) velocityY, scrollY);
return true;
}
return false;
}
private void fling(int velocityY, int scrollY) {
if (getChildCount() > 0) {
int height = getHeight() - getPaddingTop() - getPaddingBottom();
int bottom = totalHeight;
scroller.fling(0, scrollY, 0, velocityY, 0, 0, 0,
Math.max(0, bottom - height));
invalidate();
}
}
@Override
public void computeScroll() {
if (scroller.computeScrollOffset()) {
int y = scroller.getCurrY();
scrollTo(0, y);
invalidate();
}
}
@Override
public boolean onNestedFling(View target, float velocityX, float velocityY, boolean consumed) {
log("onNestedFling: target = [" + target.getClass().getName() + "], velocityX = [" + velocityX + "], velocityY = [" + velocityY + "], consumed = [" + consumed + "]");
return false;
}
@Override
public void onStopNestedScroll(View target) {
logi("======== onStopNestedScroll =======");
mParentHelper.onStopNestedScroll(target);
}
public void log(String s) {
Log.e(TAG, s);
}
public void logi(String s) {
Log.i(TAG, s);
}
public void logw(String s) {
Log.w(TAG, s);
}
}

文章来自: https://hanks.pub