Android 自定义ScrollView 支持惯性滑动，惯性回弹效果。支持上拉加载更多-阿里云开发者社区

先讲下原理：

ScrollView的子View 主要分为3部分：head头部，滚动内容，fooder底部

我们实现惯性滑动，以及回弹，都是靠超过head或者fooder 就重新滚动到，内容的顶部或者底部。

之前看了Pulltorefresh 他是通过不断改变 head或者 fooder的 pading 值来实现上拉或者下拉的效果。感觉有点不流畅，而且层次嵌套得比较多。当然他的好处是扩展性好。

因工作需求，需要层次嵌套少，对性能要求非常高。因此重新自定义了ViewGroup实现。

直接上代码：

[java] view plain copy

package com.example.administrator.customscrollview;
import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.OverScroller;
/**
* 自定义 pulltorefresh Layout
* TODO: ferris 2015年9月11日 18:52:40
*/
public class PullTorefreshScrollView extends ViewGroup {
private FoodeLayout fooder_layout;// top and buttom
private View top_layout;
private int desireWidth, desireHeight;
private VelocityTracker velocityTracker;
private int mPointerId;
private float x, y;
private OverScroller mScroller;
private int maxFlingVelocity, minFlingVelocity;
private int mTouchSlop;
protected Boolean isMove = false;
protected float downX = 0, downY = 0;
private int top_hight = 0;
private int scrollYButtom = 0;
private int nScrollYButtom = 0;
private int pullDownMin = 0;
private Boolean isEnablePullDown = true;
private Boolean isFirst=true;
public void setEnablePullDown(Boolean isEnablePullDown) {
this.isEnablePullDown = isEnablePullDown;
}
public PullTorefreshScrollView(Context context) {
super(context);
init(null, 0);
}
public PullTorefreshScrollView(Context context, AttributeSet attrs) {
super(context, attrs);
init(attrs, 0);
}
public PullTorefreshScrollView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(attrs, defStyle);
}
private void init(AttributeSet attrs, int defStyle) {
// Load attributes
// final TypedArray a = getContext().obtainStyledAttributes(
// attrs, R.styleable.PullTorefreshScrollView, defStyle, 0);
//
//
// a.recycle();
mScroller = new OverScroller(getContext());
maxFlingVelocity = ViewConfiguration.get(getContext()).getScaledMaximumFlingVelocity();
minFlingVelocity = ViewConfiguration.get(getContext()).getScaledMinimumFlingVelocity();
mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
fooder_layout = (FoodeLayout) findViewById(R.id.fooder_layout);
top_layout = findViewById(R.id.top_layout);
if (isEnablePullDown) {
fooder_layout.showFooderPull();
} else {
fooder_layout.hideFooder();
}
}
public int getScrollYTop() {
return top_hight;
}
public int getScrollYButtom() {
return scrollYButtom;
}
public int getNScrollYTop() {
return 0;
}
public int getNScrollYButtom() {
return nScrollYButtom;
}
public int measureWidth(int widthMeasureSpec) {
int result = 0;
int measureMode = MeasureSpec.getMode(widthMeasureSpec);
int width = MeasureSpec.getSize(widthMeasureSpec);
switch (measureMode) {
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = width;
break;
default:
break;
}
return result;
}
public int measureHeight(int heightMeasureSpec) {
int result = 0;
int measureMode = MeasureSpec.getMode(heightMeasureSpec);
int height = MeasureSpec.getSize(heightMeasureSpec);
switch (measureMode) {
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = height;
break;
default:
break;
}
return result;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 计算所有child view 要占用的空间
int width = measureWidth(widthMeasureSpec);
int height = measureHeight(heightMeasureSpec);
desireWidth = 0;
desireHeight = 0;
int count = getChildCount();
for (int i = 0; i < count; ++i) {
View v = getChildAt(i);
if (v.getVisibility() != View.GONE) {
LayoutParams lp = (LayoutParams) v.getLayoutParams();
measureChildWithMargins(v, widthMeasureSpec, 0,
heightMeasureSpec, 0);
//只是在这里增加了垂直或者水平方向的判断
if (v.getId() == R.id.top_layout) {
top_hight = v.getMeasuredHeight();
}
desireWidth = Math.max(desireWidth, v.getMeasuredWidth()
+ lp.leftMargin + lp.rightMargin);
desireHeight += v.getMeasuredHeight() + lp.topMargin
+ lp.bottomMargin;
}
}
// count with padding
desireWidth += getPaddingLeft() + getPaddingRight();
desireHeight += getPaddingTop() + getPaddingBottom();
// see if the size is big enough
desireWidth = Math.max(desireWidth, getSuggestedMinimumWidth());
desireHeight = Math.max(desireHeight, getSuggestedMinimumHeight());
//处理内容比较少的时候，就添加一定的高度
int scrollHight = height + top_hight * 2;
if (scrollHight > desireWidth) {
int offset = scrollHight - desireHeight;
View view = new View(getContext());
view.setBackgroundResource(R.color.top_layout_color);
LayoutParams lp = new LayoutParams(LayoutParams.MATCH_PARENT, offset);
addView(view, getChildCount() - 1, lp);
desireWidth = scrollHight;
}
setMeasuredDimension(resolveSize(desireWidth, widthMeasureSpec),
resolveSize(desireHeight, heightMeasureSpec));
scrollYButtom = desireHeight - getMeasuredHeight() - top_hight;
nScrollYButtom = desireHeight - getMeasuredHeight();
//如果上啦拖出一半的高度，就代表将要执行上啦
pullDownMin = nScrollYButtom - top_hight / 2;
if(isFirst){
scrollTo(0, top_hight);
isFirst=false;
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
final int parentLeft = getPaddingLeft();
final int parentRight = r - l - getPaddingRight();
final int parentTop = getPaddingTop();
final int parentBottom = b - t - getPaddingBottom();
if (BuildConfig.DEBUG)
Log.d("onlayout", "parentleft: " + parentLeft + " parenttop: "
+ parentTop + " parentright: " + parentRight
+ " parentbottom: " + parentBottom);
int left = parentLeft;
int top = parentTop;
int count = getChildCount();
for (int i = 0; i < count; ++i) {
View v = getChildAt(i);
if (v.getVisibility() != View.GONE) {
LayoutParams lp = (LayoutParams) v.getLayoutParams();
final int childWidth = v.getMeasuredWidth();
final int childHeight = v.getMeasuredHeight();
final int gravity = lp.gravity;
final int horizontalGravity = gravity
& Gravity.HORIZONTAL_GRAVITY_MASK;
final int verticalGravity = gravity
& Gravity.VERTICAL_GRAVITY_MASK;
// layout vertical, and only consider horizontal gravity
left = parentLeft;
top += lp.topMargin;
switch (horizontalGravity) {
case Gravity.LEFT:
break;
case Gravity.CENTER_HORIZONTAL:
left = parentLeft
+ (parentRight - parentLeft - childWidth) / 2
+ lp.leftMargin - lp.rightMargin;
break;
case Gravity.RIGHT:
left = parentRight - childWidth - lp.rightMargin;
break;
}
v.layout(left, top, left + childWidth, top + childHeight);
top += childHeight + lp.bottomMargin;
}
}
}
@Override
protected android.view.ViewGroup.LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);
}
@Override
public android.view.ViewGroup.LayoutParams generateLayoutParams(
AttributeSet attrs) {
return new LayoutParams(getContext(), attrs);
}
@Override
protected android.view.ViewGroup.LayoutParams generateLayoutParams(
android.view.ViewGroup.LayoutParams p) {
return new LayoutParams(p);
}
public static class LayoutParams extends MarginLayoutParams {
public int gravity = -1;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
TypedArray ta = c.obtainStyledAttributes(attrs,
R.styleable.SlideGroup);
gravity = ta.getInt(R.styleable.SlideGroup_layout_gravity, -1);
ta.recycle();
}
public LayoutParams(int width, int height) {
this(width, height, -1);
}
public LayoutParams(int width, int height, int gravity) {
super(width, height);
this.gravity = gravity;
}
public LayoutParams(android.view.ViewGroup.LayoutParams source) {
super(source);
}
public LayoutParams(MarginLayoutParams source) {
super(source);
}
}
/**
* onInterceptTouchEvent()用来询问是否要拦截处理。 onTouchEvent()是用来进行处理。
*
* 例如：parentLayout----childLayout----childView 事件的分发流程：
* parentLayout::onInterceptTouchEvent()---false?--->
* childLayout::onInterceptTouchEvent()---false?--->
* childView::onTouchEvent()---false?--->
* childLayout::onTouchEvent()---false?---> parentLayout::onTouchEvent()
*
*
*
* 如果onInterceptTouchEvent()返回false，且分发的子View的onTouchEvent()中返回true，
* 那么onInterceptTouchEvent()将收到所有的后续事件。
*
* 如果onInterceptTouchEvent()返回true，原本的target将收到ACTION_CANCEL，该事件
* 将会发送给我们自己的onTouchEvent()。
*/
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
final int action = ev.getActionMasked();
if (BuildConfig.DEBUG)
Log.d("onInterceptTouchEvent", "action: " + action);
if (action == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {
// 该事件可能不是我们的
return false;
}
boolean isIntercept = false;
switch (action) {
case MotionEvent.ACTION_DOWN:
// 如果动画还未结束，则将此事件交给onTouchEvet()处理，
// 否则，先分发给子View
isIntercept = !mScroller.isFinished();
// 如果此时不拦截ACTION_DOWN时间，应该记录下触摸地址及手指id，当我们决定拦截ACTION_MOVE的event时，
// 将会需要这些初始信息（因为我们的onTouchEvent将可能接收不到ACTION_DOWN事件）
mPointerId = ev.getPointerId(0);
// if (!isIntercept) {
downX = x = ev.getX();
downY = y = ev.getY();
// }
break;
case MotionEvent.ACTION_MOVE:
int pointerIndex = ev.findPointerIndex(mPointerId);
if (BuildConfig.DEBUG)
Log.d("onInterceptTouchEvent", "pointerIndex: " + pointerIndex
+ ", pointerId: " + mPointerId);
float mx = ev.getX(pointerIndex);
float my = ev.getY(pointerIndex);
if (BuildConfig.DEBUG)
Log.d("onInterceptTouchEvent", "action_move [touchSlop: "
+ mTouchSlop + ", deltaX: " + (x - mx) + ", deltaY: "
+ (y - my) + "]");
// 根据方向进行拦截，（其实这样，如果我们的方向是水平的，里面有一个ScrollView，那么我们是支持嵌套的）
if (Math.abs(y - my) >= mTouchSlop) {
isIntercept = true;
}
//如果不拦截的话，我们不会更新位置，这样可以通过累积小的移动距离来判断是否达到可以认为是Move的阈值。
//这里当产生拦截的话，会更新位置（这样相当于损失了mTouchSlop的移动距离，如果不更新，可能会有一点点跳的感觉）
if (isIntercept) {
x = mx;
y = my;
}
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
// 这是触摸的最后一个事件，无论如何都不会拦截
if (velocityTracker != null) {
velocityTracker.recycle();
velocityTracker = null;
}
break;
case MotionEvent.ACTION_POINTER_UP:
solvePointerUp(ev);
break;
}
return isIntercept;
}
private void solvePointerUp(MotionEvent event) {
// 获取离开屏幕的手指的索引
int pointerIndexLeave = event.getActionIndex();
int pointerIdLeave = event.getPointerId(pointerIndexLeave);
if (mPointerId == pointerIdLeave) {
// 离开屏幕的正是目前的有效手指，此处需要重新调整，并且需要重置VelocityTracker
int reIndex = pointerIndexLeave == 0 ? 1 : 0;
mPointerId = event.getPointerId(reIndex);
// 调整触摸位置，防止出现跳动
x = event.getX(reIndex);
y = event.getY(reIndex);
if (velocityTracker != null)
velocityTracker.clear();
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
final int action = event.getActionMasked();
if (velocityTracker == null) {
velocityTracker = VelocityTracker.obtain();
}
velocityTracker.addMovement(event);
switch (action) {
case MotionEvent.ACTION_DOWN:
// 获取索引为0的手指id
isMove = false;
mPointerId = event.getPointerId(0);
x = event.getX();
y = event.getY();
if (!mScroller.isFinished())
mScroller.abortAnimation();
break;
case MotionEvent.ACTION_MOVE:
isMove = true;
// 获取当前手指id所对应的索引，虽然在ACTION_DOWN的时候，我们默认选取索引为0
// 的手指，但当有第二个手指触摸，并且先前有效的手指up之后，我们会调整有效手指
// 屏幕上可能有多个手指，我们需要保证使用的是同一个手指的移动轨迹，
// 因此此处不能使用event.getActionIndex()来获得索引
final int pointerIndex = event.findPointerIndex(mPointerId);
float mx = event.getX(pointerIndex);
float my = event.getY(pointerIndex);
moveBy((int) (x - mx), (int) (y - my));
x = mx;
y = my;
break;
case MotionEvent.ACTION_UP:
isMove = false;
velocityTracker.computeCurrentVelocity(1000, maxFlingVelocity);
float velocityX = velocityTracker.getXVelocity(mPointerId);
float velocityY = velocityTracker.getYVelocity(mPointerId);
completeMove(-velocityX, -velocityY);
if (velocityTracker != null) {
velocityTracker.recycle();
velocityTracker = null;
}
break;
case MotionEvent.ACTION_POINTER_UP:
// 获取离开屏幕的手指的索引
isMove = false;
int pointerIndexLeave = event.getActionIndex();
int pointerIdLeave = event.getPointerId(pointerIndexLeave);
if (mPointerId == pointerIdLeave) {
// 离开屏幕的正是目前的有效手指，此处需要重新调整，并且需要重置VelocityTracker
int reIndex = pointerIndexLeave == 0 ? 1 : 0;
mPointerId = event.getPointerId(reIndex);
// 调整触摸位置，防止出现跳动
x = event.getX(reIndex);
y = event.getY(reIndex);
if (velocityTracker != null)
velocityTracker.clear();
}
break;
case MotionEvent.ACTION_CANCEL:
isMove = false;
break;
}
return true;
}
private Boolean isPull = false;
//此处的moveBy是根据水平或是垂直排放的方向，
//来选择是水平移动还是垂直移动
public void moveBy(int deltaX, int deltaY) {
if (BuildConfig.DEBUG)
Log.d("moveBy", "deltaX: " + deltaX + " deltaY: " + deltaY);
if (Math.abs(deltaY) >= Math.abs(deltaX)) {
int mScrollY = getScrollY();
if (mScrollY <= 0) {
scrollTo(0, 0);
} else if (mScrollY >= getNScrollYButtom()) {
scrollTo(0, getNScrollYButtom());
} else {
scrollBy(0, deltaY);
}
if (isEnablePullDown && deltaY > 0 && mScrollY >= pullDownMin) {
isPull = true;
Log.d("onlayout", "isPull: true");
}
}
}
private void completeMove(float velocityX, float velocityY) {
int mScrollY = getScrollY();
int maxY = getScrollYButtom();
int minY = getScrollYTop();
if (mScrollY >= maxY) {//如果滚动，超过了下边界，就回弹到下边界
if (isPull) {//滚动到最底部
mScroller.startScroll(0, mScrollY, 0, getNScrollYButtom() - mScrollY, 300);
invalidate();
//显示雷达
fooder_layout.showFooderRadar();
if (pullDownListem != null) {
pullDownListem.onPullDown();
}
Log.d("onlayout", "isPull: true 滚动到最底部，显示出雷达");
} else {
mScroller.startScroll(0, mScrollY, 0, maxY - mScrollY);
invalidate();
Log.d("onlayout", "isPull: true");
}
} else if (mScrollY <= minY) {//如果滚动，超过了上边界，就回弹到上边界
// 超出了上边界，弹回
mScroller.startScroll(0, mScrollY, 0, minY - mScrollY);
invalidate();
} else if (Math.abs(velocityY) >= minFlingVelocity && maxY > 0) {//大于1页的时候
// mScroller.fling(0, mScrollY, 0, (int) (velocityY * 1.2f), 0, 0, minY, maxY);
mScroller.fling(0, mScrollY, 0, (int) (velocityY * 2f), 0, 0, getNScrollYTop(), getNScrollYButtom());
invalidate();
}
}
public void ifNeedScrollBack() {
int mScrollY = getScrollY();
int maxY = getScrollYButtom();
int minY = getScrollYTop();
if (mScrollY > maxY) {
// 超出了下边界，弹回
mScroller.startScroll(0, mScrollY, 0, maxY - mScrollY);
invalidate();
} else if (mScrollY < minY) {
// 超出了上边界，弹回
mScroller.startScroll(0, mScrollY, 0, minY - mScrollY);
invalidate();
}
}
@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
super.onScrollChanged(l, t, oldl, oldt);
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(0, mScroller.getCurrY());
postInvalidate();
} else {
Log.d("onlayout", "computeScroll,isMove:"+isMove+",isPull:"+isPull);
if (!isMove && !isPull) {
ifNeedScrollBack();
}
}
}
public void onPullSuccess() {
soomToBack();
}
public void soomToBack() {
int mScrollY = getScrollY();
int maxY = getScrollYButtom();
Log.d("onlayout", "soomToBack: (maxY - mScrollY)="+(maxY - mScrollY)+"，maxY="+maxY+",mScrollY="+mScrollY);
// 超出了下边界，弹回
mScroller.startScroll(0, mScrollY, 0, maxY - mScrollY, 300);
invalidate();
postDelayed(new Runnable() {
@Override
public void run() {
fooder_layout.showFooderPull();
isPull = false;
}
}, 310);
}
private PullDownListem pullDownListem;
public void setPullDownListem(PullDownListem pullDownListem) {
this.pullDownListem = pullDownListem;
}
public interface PullDownListem {
public void onPullDown();
}
}

本文转自莫水千流博客园博客，原文链接：http://www.cnblogs.com/zhoug2020/p/6076194.html，如需转载请自行联系原作者

Android 自定义ScrollView 支持惯性滑动，惯性回弹效果。支持上拉加载更多

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