这篇文章主要介绍了Android中ViewDragHelper如何实现京东、淘宝拖拽详情功能，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。
效果图如下所述：
要实现这个效果有三种方式：
① 手势
② 动画
③ ViewDragHelper
这里我使用的是ViewDragHelper类.
public class ViewDragLayout extends ViewGroup {
//垂直方向的滑动速度
private static final int VEL_THRESHOLD = 300;
//垂直方向的滑动距离
private static final int DISTANCE_THRESHOLD = 300;
//上面可见的View
private View mTopView;
//下面详情View
private View mBottomView;
//ViewDragHelper实例
private ViewDragHelper mViewDragHelper;
private GestureDetectorCompat mGestureDetectorCompat;
private int mFirstHeight;
public ViewDragLayout(Context context) {
super(context);
init();
}
public ViewDragLayout(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
public ViewDragLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
public ViewDragLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
super(context, attrs, defStyleAttr, defStyleRes);
init();
}
private void init() {
mViewDragHelper = ViewDragHelper.create(this, 1.0f, new DragHelperCallback());
mGestureDetectorCompat = new GestureDetectorCompat(getContext(), new YScrollDetector());
}
@Override
protected void onFinishInflate() {
super.onFinishInflate();
mTopView = getChildAt(0);
mBottomView = getChildAt(1);
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (mTopView.getTop() == 0) {
mTopView.layout(l, 0, r, b-t );
mBottomView.layout(l, 0, r, b-t );
mFirstHeight = mTopView.getMeasuredHeight();
mBottomView.offsetTopAndBottom(mFirstHeight);
}else{
mTopView.layout(l, mTopView.getTop(), r, mTopView.getBottom());
mBottomView.layout(l, mBottomView.getTop(), r, mBottomView.getBottom());
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
measureChildren(widthMeasureSpec,heightMeasureSpec);
int maxWidth = MeasureSpec.getSize(widthMeasureSpec);
int maxHeight = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, 0),
resolveSizeAndState(maxHeight, heightMeasureSpec, 0));
}
private class DragHelperCallback extends ViewDragHelper.Callback {
@Override
public boolean tryCaptureView(View child, int pointerId) {
return true;
}
/**
* @param child
* @param top
* @param dy
* @return
*/
@Override
public int clampViewPositionVertical(View child, int top, int dy) {
int finalTop=top;
if (child == mTopView) {
if (top > 0) {
finalTop=0;
}
}else if(child==mBottomView){
if(top<0){
finalTop=0;
}
}
return finalTop;
}
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
if (changedView == mTopView) {
mBottomView.offsetTopAndBottom(dy);
}else if (changedView==mBottomView){
mTopView.offsetTopAndBottom(dy);
}
ViewCompat.postInvalidateOnAnimation(ViewDragLayout.this);
}
/**
*
* @param releasedChild
* @param xvel 水平方向的速度（向右为正）
* @param yvel 竖直方向的速度（向下为正）
*/
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
animTopOrBottom(releasedChild, yvel);
}
}
//动画实现滚动
private void animTopOrBottom(View releasedChild, float yvel) {
int finalTop=0;
if (releasedChild == mTopView) {
if (yvel < -VEL_THRESHOLD || (releasedChild.getTop() < -DISTANCE_THRESHOLD)) {
finalTop=-mFirstHeight;
}
} else if (releasedChild == mBottomView) {
if (yvel > VEL_THRESHOLD || (releasedChild.getTop() > DISTANCE_THRESHOLD)) {
finalTop=mFirstHeight;
}
}
if (mViewDragHelper.smoothSlideViewTo(releasedChild, 0, finalTop)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
@Override
public void computeScroll() {
if (mViewDragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
//是否拦截手势操作
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (mTopView.getTop() < 0 && mTopView.getBottom() > 0) {
return false;
}
boolean isCanTouch = mGestureDetectorCompat.onTouchEvent(ev);
boolean shouldIntercept = mViewDragHelper.shouldInterceptTouchEvent(ev);
if (ev.getActionMasked() == MotionEvent.ACTION_DOWN) {
mViewDragHelper.processTouchEvent(ev);
}
return isCanTouch&&shouldIntercept;
}
//将touch事件交给ViewDragHelper处理
@Override
public boolean onTouchEvent(MotionEvent event) {
mViewDragHelper.processTouchEvent(event);
return true;
}
//垂直方向上才滚动
private class YScrollDetector extends GestureDetector.SimpleOnGestureListener {
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
return Math.abs(distanceY) > Math.abs(distanceX);
}
}
}使用ViewDragLayout
<gesture.com.cn.widget.ViewDragLayout android:id="@+id/view_drag_layout" android:layout_width="match_parent" android:layout_height="match_parent" > <FrameLayout android:id="@+id/top_fragment_view" android:layout_width="match_parent" android:layout_height="match_parent" /> <FrameLayout android:id="@+id/bottom_fragment_view" android:layout_width="match_parent" android:layout_height="match_parent"/> </gesture.com.cn.widget.ViewDragLayout>
bottom_fragment_view中使用了ScrollView，但是原生是不行的，所以这里我又将ScrollView重写了一下
这里主要是处理dispatchTouchEvent(MotionEvent ev)方法，判断将touch事件交给自己处理还是交给父View处理
public class CustomScrollView extends ScrollView {
//滚动临界值
private int mTouchSlop;
//获取初始X坐标
private float mRawX;
//获取初始Y坐标
private float mRawY;
//是否向上滑动
private boolean mCanScrollUp;
//是否向下滑动
private boolean mCanScrollDown;
public CustomScrollView(Context context) {
super(context);
init();
}
public CustomScrollView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
init();
}
public CustomScrollView(Context context, @Nullable AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}
private void init() {
ViewConfiguration configuration = ViewConfiguration.get(getContext());
mTouchSlop = configuration.getScaledTouchSlop();
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
switch (ev.getActionMasked()) {
case MotionEvent.ACTION_DOWN:
mRawX = ev.getRawX();
mRawY = ev.getRawY();
mCanScrollUp = canScrollingUp();
mCanScrollDown = canScrollingDown();
//表示子View要自己消费这次事件，告诉父View不拦截这次的事件。
getParent().requestDisallowInterceptTouchEvent(true);
break;
case MotionEvent.ACTION_MOVE:
float xDis = Math.abs(mRawX - ev.getRawX());
float yDis = Math.abs(mRawY - ev.getRawY());
if (yDis > xDis && yDis > mTouchSlop) {
if (mRawY < ev.getRawY() && mCanScrollUp) {
//表示子View不消费这次事件，告诉父View拦截这次的事件。
getParent().requestDisallowInterceptTouchEvent(false);
return false;
}
if (mRawY > ev.getRawY() && mCanScrollDown) {
//表示子View不消费这次事件，告诉父View拦截这次的事件。
getParent().requestDisallowInterceptTouchEvent(false);
return false;
}
}
break;
}
return super.dispatchTouchEvent(ev);
}
/**
* 手指向下滑动（内容向上滑动）
* @return
*/
private boolean canScrollingUp() {
if (ViewCompat.canScrollVertically(this, -1)) {
return false;
} else {
return true;
}
}
/**
* 手指向上滑动（内容向下滑动）
* @return
*/
private boolean canScrollingDown() {
if (ViewCompat.canScrollVertically(this, 1)) {
return false;
} else {
return true;
}
}
}好了，具体拖拽代码就是这些了，界面我用的两个Fragment，相信大家也看出来了。里面大家换成自己的业务UI就可以了。
感谢你能够认真阅读完这篇文章，希望小编分享的“Android中ViewDragHelper如何实现京东、淘宝拖拽详情功能”这篇文章对大家有帮助，同时也希望大家多多支持亿速云，关注亿速云行业资讯频道，更多相关知识等着你来学习!
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