Android实现滑动效果

case MotionEvent.ACTION_MOVE:
  //计算偏移量
  int offsetX=x-lastX;
  int offsetY=y-lastY;   
  layout(getLeft()+offsetX,getTop()+offsetY,getRight()+offsetX,getBottom()+offsetY);
  break;

offsetLeftAndRight(offsetX);
offsetTopAndBottom(offsetY);

LinearLayout.LayoutParams params= (LinearLayout.LayoutParams) getLayoutParams();
params.leftMargin= getLeft()+offsetX;
params.topMargin= getTop()+offsetY;
setLayoutParams(params);

int offsetX=x-lastX;
int offsetY=y-lastY;
View parent= (View) getParent();
parent.scrollBy(-offsetX,-offsetY);

@Override
 public void computeScroll() {
 super.computeScroll();
 //判断scroller是否执行完毕
 if (scroller.computeScrollOffset()){
 View view= (View) getParent();
  //获得当前的滑动坐标
 view.scrollTo(scroller.getCurrX(),scroller.getCurrY());
 //通过重绘来不断调用computeScroll
 invalidate();
 //invalidate()--->draw()---->computeScroll()
 }
 }

case MotionEvent.ACTION_UP:
 //手指离开时，执行滑动过程
 View viewGroup= (View) getParent();
 scroller.startScroll(
  viewGroup.getScrollX(),
  viewGroup.getScrollY(),
  -viewGroup.getScrollX(),
  -viewGroup.getScrollY(),500);
 invalidate();
 break;

public class DrawGroup extends FrameLayout {
 private ViewDragHelper helper;
 private View mainView,menuView;

 public DrawGroup(@NonNull Context context) {
 super(context);
 inView();

 }

 public DrawGroup(@NonNull Context context, @Nullable AttributeSet attrs) {
 super(context, attrs);
 inView();
 }

 public DrawGroup(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
 super(context, attrs, defStyleAttr);
 inView();
 }
 private void inView(){
 helper=ViewDragHelper.create(this, new ViewDragHelper.Callback() {
 @Override
 public boolean tryCaptureView(@NonNull View child, int pointerId) {
 //如果当前触摸的child是mainView时开始检测
 return child==mainView;
 }

 @Override
 public int clampViewPositionHorizontal(@NonNull View child, int left, int dx) {
 //水平方向上的滑动
 return left;
 }

 @Override
 public int clampViewPositionVertical(@NonNull View child, int top, int dy) {
 //垂直方向上的滑动
 return 0;
 }

 @Override
 public void onViewReleased(@NonNull View releasedChild, float xvel, float yvel) {
 //拖动结束后调用
 super.onViewReleased(releasedChild, xvel, yvel);
 //手指抬起后缓慢移动到指定位置
 if (mainView.getLeft()<300){
  //关闭菜单
  helper.smoothSlideViewTo(mainView,0,0);
  //相当于scroller的startScroll方法
 }else {
  //打开菜单
  helper.smoothSlideViewTo(mainView,300,0);
 }
 ViewCompat.postInvalidateOnAnimation(DrawGroup.this);
 }
 });
 }

 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
 return helper.shouldInterceptTouchEvent(ev);
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
 //将触摸事件传递给ViewDragHelper，此操作必不可少
 helper.processTouchEvent(event);
 return true;
 }

 @Override
 public void computeScroll() {
 if (helper.continueSettling(true)){
 ViewCompat.postInvalidateOnAnimation(this);
 }
 }

 @Override
 protected void onFinishInflate() {
 super.onFinishInflate();
 //加载完布局调用
 menuView=getChildAt(0);
 mainView=getChildAt(1);
 }

 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
 super.onSizeChanged(w, h, oldw, oldh);
 }
}