重写ViewGroup并借助ViewDragHelper实现各种拖拽交互效果（一）

一般实现比较复杂的交互效果，都会选择重写ViewGroup，并通过onTouchEvent和onInterceptTouchEvent等实现对各种事件的处理，但对事件的处理是很不容易的一个事情。

本文主要是借助v4包中的ViewDragHelper这个帮助类，来重写ViewGroup，把事件完全交给帮助类去完成，并借助帮助类的几个回调方法来完成各种复杂交互效果，完全避开了事件处理。

对ViewDragHelper的使用，网上有很多资料，在此就不重新介绍了，这里我通过两个实现的例子，以及例子中的注释，来让大家明白怎么轻松实现各种效果。

一、带手柄的侧滑菜单效果HandleDrawerLayout

Android v4包中自带侧滑菜单效果DrawerLayout是很好的一种交互，但是某些需求下，需要多一个类似手柄的东西来拉开和关闭侧滑菜单，用DrawerLayout是尝遍各种方式都无法实现。看以下效果图就明白了

1、布局文件：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!--内部的布局需要按照1、2、3的顺序，3嵌套4、5布局的结构来布局-->
    <com.dway.testwork.viewdrag.HandleDrawerLayout
        android:id="@+id/hdl_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!--1 内容布局-->
        <FrameLayout
            android:id="@+id/hdl_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#f7f7f7">
        </FrameLayout>

        <!--2 内容布局上面的半透明布局-->
        <View
            android:id="@+id/hdl_scrim"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#7f000000"/>

        <!--3 侧滑菜单布局和手柄布局的父布局-->
        <LinearLayout
            android:id="@+id/hdl_drawer_group"
            android:layout_width="wrap_content"
            android:layout_height="match_parent"
            android:orientation="horizontal">
            <!--4 侧滑菜单布局-->
            <FrameLayout
                android:id="@+id/hdl_menu_view"
                android:layout_width="245dp"
                android:layout_height="match_parent"
                android:background="#2d3144">
            </FrameLayout>
            <!--5 侧滑手柄布局-->
            <RelativeLayout
                android:id="@+id/hdl_handle_view"
                android:layout_width="40dp"
                android:layout_height="173dp"
                android:gravity="center"
                android:layout_gravity="center_vertical"
                android:background="#3fff00ff">
                <TextView
                    android:id="@+id/hdl_handle_view_text"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:ems="1"
                    android:maxEms="1"
                    android:gravity="center"
                    android:textSize="23sp"
                    android:text="我是手柄"
                    android:layout_gravity="center_vertical" />
            </RelativeLayout>
        </LinearLayout>
    </com.dway.testwork.viewdrag.HandleDrawerLayout>

</FrameLayout>

2、布局类HandleDrawerLayout.java：

package com.dway.testwork.viewdrag;

import android.content.Context;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

/**
 * 带手柄的侧滑菜单布局。
 * drawer收起的时候，menu不可见，但是handle可见
 * 布局内部结构包含：content、scrim（drawer打开后的半透明背景）、drawer（为横向LinearLayout布局，包含menu和handle）
 * Created by dway on 2017/12/19.
 */
public class HandleDrawerLayout extends ViewGroup {

    //内容view
    private View mContentView;
    //当侧滑菜单展开时，显示在mContentView上面的半透明view
    private View mScrimView;
    //侧滑菜单和手柄组成的布局，因为侧滑菜单和手柄是同时移动的，所以套了一层父布局，方便一起移动
    private ViewGroup mDrawerGroup;
    //mDrawerGroup中的菜单view
    private View mMenuView;
    //mDrawerGroup中的手柄view
    private View mHandleView;

    //强大的帮助类
    private ViewDragHelper mHelper;

    //菜单展开的程度。取值在0到1之间，0表示侧滑菜单隐藏，1表示侧滑菜单完全展开
    private float mOpenPercent = 0;

    private boolean mInLayout = false;
    private boolean mFirstLayout = true;

    public HandleDrawerLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        mHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {
            @Override
            public int clampViewPositionHorizontal(View child, int left, int dx) {
                // 限定child横向的座标范围：
                // 参数left是child想要移动到left位置（仅仅是想移动，但还没移动）
                // 如果不想child在X轴上被移动，返回0
                if(child == mDrawerGroup){
                    // 这里代表-mMenuView.getMeasuredWidth() <= left <= 0
                    // 即child的横向座标只能在这个范围内
                    return Math.max(-mMenuView.getMeasuredWidth(), Math.min(left, 0));
                }
                return 0;
            }

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                // 限定child纵向的座标范围，此处暂没用到
                return super.clampViewPositionVertical(child, top, dy);
            }

            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                // 粗碰child时对child进行尝试捕获，返回true代表该view可以被捕获，false则相反
                // 比如手指按下child这个view时，如果需要交互操作则返回true
                return child == mDrawerGroup;
            }

            @Override
            public void onEdgeDragStarted(int edgeFlags, int pointerId) {
                // 边缘检测，可通过下面的mHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT)设置左右上下边缘检测
                // 以下代表屏幕左边缘划进来，强制捕获到mDrawerGroup，相当于人工的tryCaptureView
                mHelper.captureChildView(mDrawerGroup, pointerId);
            }

            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                // 松开手的时候，释放view，根据当前速度做相应处理
                if(releasedChild == mDrawerGroup){
                    int menuViewWidth = mMenuView.getWidth();
                    float offset = (menuViewWidth + releasedChild.getLeft()) * 1.0f / menuViewWidth;
                    // 设置释放后的view慢慢移动到指定位置
                    mHelper.settleCapturedViewAt(xvel > 0 || xvel == 0 && offset > 0.5f ? 0 : -menuViewWidth, releasedChild.getTop());
                    // 要调用invalidate()才会开始移动
                    invalidate();
                }
            }

            @Override
            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
                // 被捕获的view位置改变的回调，left和top为changedView即将移动到的位置
                if(changedView == mDrawerGroup){
                    int menuViewWidth = mMenuView.getWidth();
                    mOpenPercent = (float) (menuViewWidth + left) / menuViewWidth;

                    mScrimView.setAlpha(mOpenPercent);
                    if(floatCompare(mOpenPercent, 0f)){
                        mScrimView.setVisibility(GONE);
                    }else{
                        mScrimView.setVisibility(VISIBLE);
                    }

                    if(mDrawerListener != null){
                        mDrawerListener.onDrawer(mOpenPercent);
                    }
                }
            }

            @Override
            public int getViewHorizontalDragRange(View child) {
                //指定child横向可拖拽的范围
                return child == mDrawerGroup ? mMenuView.getWidth() : 0;
            }
        });
        // 设置左边缘检测，即从屏幕左边划进屏幕时，会回调onEdgeDragStarted
        mHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // 设置各个子view的大小
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(widthSize, heightSize);

        // 按照xml文件的布局，获取各个子view
        mContentView = getChildAt(0);
        mScrimView = getChildAt(1);
        mDrawerGroup = (ViewGroup) getChildAt(2);
        mMenuView = mDrawerGroup.getChildAt(0);
        mHandleView = mDrawerGroup.getChildAt(1);

        MarginLayoutParams lp = (MarginLayoutParams) mContentView.getLayoutParams();
        int contentWidthSpec = MeasureSpec.makeMeasureSpec(
                widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
        int contentHeightSpec = MeasureSpec.makeMeasureSpec(
                heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);
        mContentView.measure(contentWidthSpec, contentHeightSpec);

        lp = (MarginLayoutParams) mScrimView.getLayoutParams();
        int bgWidthSpec = MeasureSpec.makeMeasureSpec(
                widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
        int bgHeightSpec = MeasureSpec.makeMeasureSpec(
                heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);
        mScrimView.measure(bgWidthSpec, bgHeightSpec);

        lp = (MarginLayoutParams) mDrawerGroup.getLayoutParams();
        int menuGroupWidthSpec = getChildMeasureSpec(widthMeasureSpec,
                lp.leftMargin + lp.rightMargin, lp.width);
        int menuGroupHeightSpec = getChildMeasureSpec(heightMeasureSpec,
                lp.topMargin + lp.bottomMargin, lp.height);
        mDrawerGroup.measure(menuGroupWidthSpec, menuGroupHeightSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        // 设置各子view的位置，注意第一次初始化位置和以后设置的位置略有区别
        mInLayout = true;
        MarginLayoutParams lp = (MarginLayoutParams) mContentView.getLayoutParams();
        mContentView.layout(lp.leftMargin, lp.topMargin,
                lp.leftMargin + mContentView.getMeasuredWidth(),
                lp.topMargin + mContentView.getMeasuredHeight());

        lp = (MarginLayoutParams) mScrimView.getLayoutParams();
        mScrimView.layout(lp.leftMargin, lp.topMargin,
                lp.leftMargin + mScrimView.getMeasuredWidth(),
                lp.topMargin + mScrimView.getMeasuredHeight());

        lp = (MarginLayoutParams) mDrawerGroup.getLayoutParams();
        int groupLeft;// = - mMenuView.getMeasuredWidth() + lp.leftMargin;
        if(mFirstLayout){
            groupLeft = - mMenuView.getMeasuredWidth() + lp.leftMargin;
        }else{
            groupLeft = mDrawerGroup.getLeft();
        }
        mDrawerGroup.layout(groupLeft, lp.topMargin,
                groupLeft + mDrawerGroup.getMeasuredWidth(),
                lp.topMargin + mDrawerGroup.getMeasuredHeight());

        initScrimView();

        mInLayout = false;
        mFirstLayout = false;
    }

    @Override
    public void requestLayout() {
        if(!mInLayout) {
            super.requestLayout();
        }
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        mFirstLayout = true;
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        mFirstLayout = true;
    }

    private void initScrimView(){
        if(mFirstLayout && mScrimView != null){
            mScrimView.setAlpha(mOpenPercent);
            if(floatCompare(mOpenPercent, 0f)){
                mScrimView.setVisibility(GONE);
            }else{
                mScrimView.setVisibility(VISIBLE);
            }
            mScrimView.setOnClickListener(onClickListener);
        }
    }

    private OnClickListener onClickListener = new OnClickListener() {
        @Override
        public void onClick(View v) {
            if(isDrawerOpen()){
                closeDrawer();
            }
        }
    };

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        // 把事件处理交给ViewDragHelper
        return mHelper.shouldInterceptTouchEvent(ev);
    }


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // 把事件处理交给ViewDragHelper
        mHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        // 滚动过程的计算，也是交给ViewDragHelper，按以下这么写就好了
        if (mHelper.continueSettling(true)) {
            invalidate();
        }
    }

    // 以下三个方法需要重写，没啥特殊要求直接返回MarginLayoutParams就可以了

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new MarginLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected LayoutParams generateLayoutParams(LayoutParams p) {
        return new MarginLayoutParams(p);
    }


    /**
     * 两个float类型的大小比较
     * @return true 相等，false 不相等
     */
    private boolean floatCompare(float f1, float f2){
        return Math.abs(f1 - f2) < Float.MIN_VALUE;
    }

    /**
     * 是否drawer已打开。float相等直接比较可能有存在问题
     */
    public boolean isDrawerOpen(){
        return floatCompare(mOpenPercent, 1f);
    }

    /**
     * 打开drawer
     */
    public void openDrawer() {
        mOpenPercent = 1.0f;
        mHelper.smoothSlideViewTo(mDrawerGroup, 0, mDrawerGroup.getTop());
        invalidate();
    }

    /**
     * 关闭drawer
     */
    public void closeDrawer() {
        mOpenPercent = 0.0f;
        mHelper.smoothSlideViewTo(mDrawerGroup, -mMenuView.getWidth(), mDrawerGroup.getTop());
        invalidate();
    }

    private OnDrawerListener mDrawerListener = null;

    /**
     * 外部可设置监听drawer的位置回调
     * @param listener
     */
    public void setOnDrawerListener(OnDrawerListener listener) {
        mDrawerListener = listener;
    }

    public interface OnDrawerListener{
        /**
         * 抽屉打开关闭过程监听
         * @param percent 取值区间[0, 1]，0代表完全关闭，1代表完全打开
         */
        void onDrawer(float percent);
    }

}

3、Activity中也可以设置手柄的点击处理：

final HandleDrawerLayout handleDrawerLayout = getActivity().findViewById(R.id.hdl_layout);
		View handleView = getActivity().findViewById(R.id.hdl_handle_view);
		handleView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(handleDrawerLayout.isDrawerOpen()){
                    handleDrawerLayout.closeDrawer();
                }else{
                    handleDrawerLayout.openDrawer();
                }
            }
        });

二、可上下切换，类似纵向的ViewPager，并且上划时向下弹出菜单效果。以下的注释会比较少，因为跟上面的例子类似，所以不过多注释。看效果图：

1、布局文件：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.dway.testwork.viewdrag.SlideUpLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:visibility="visible">

        <FrameLayout
            android:id="@+id/slide_layout_up"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#1f00ffff">
            <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:gravity="center"
                android:text="up"/>
        </FrameLayout>
        <FrameLayout
            android:id="@+id/slide_layout_down"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#1fffff00">
            <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:gravity="center"
                android:text="down"/>
        </FrameLayout>
        <FrameLayout
            android:id="@+id/slide_layout_slide"
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:clickable="true"
            android:background="#1fff00ff">
            <TextView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:gravity="center"
                android:text="slide"/>
        </FrameLayout>

    </com.dway.testwork.viewdrag.SlideUpLayout>

</FrameLayout>

2、SlideUpLayout.java类：

package com.dway.testwork.viewdrag;

import android.content.Context;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

/**
 * 可上下切换，类似纵向的ViewPager，并且上划时向下弹出菜单效果
 * Created by dway on 2018/1/23.
 */

public class SlideUpLayout extends ViewGroup {

    private View mUpView;
    private View mDownView;
    private View mSlideView;

    private ViewDragHelper mHelper;
    
    //上下滑的程度，0表示在upView，1表示在downView
    private float mSlidePercent = 0;

    private boolean mInLayout = false;
    private boolean mFirstLayout = true;


    public SlideUpLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        mHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {

            @Override
            public int clampViewPositionVertical(View child, int top, int dy) {
                if(child == mUpView){
                    return Math.max(- mUpView.getMeasuredHeight() + mSlideView.getMeasuredHeight(), Math.min(top, 0));
                }else if(child == mDownView){
                    return Math.max(mSlideView.getMeasuredHeight(), Math.min(top, mUpView.getMeasuredHeight()));
                }else if(child == mSlideView){
                    return Math.max(- mSlideView.getMeasuredHeight(), Math.min(top, 0));
                }
                return 0;
            }

            @Override
            public boolean tryCaptureView(View child, int pointerId) {
                return child == mUpView || child == mDownView;
            }

            @Override
            public void onViewReleased(View releasedChild, float xvel, float yvel) {
                if(releasedChild == mUpView){
                    int upViewHeight = mUpView.getMeasuredHeight();
                    int slideViewHeight = mSlideView.getMeasuredHeight();
                    float offset = (upViewHeight + releasedChild.getTop() - slideViewHeight) * 1.0f / (upViewHeight - slideViewHeight);
                    mHelper.settleCapturedViewAt(releasedChild.getLeft(), yvel > 0 || yvel == 0 && offset > 0.5f ? 0 : -upViewHeight + slideViewHeight);
                    invalidate();
                }else if(releasedChild == mDownView){
                    int downViewHeight = mDownView.getMeasuredHeight();
                    int slideViewHeight = mSlideView.getMeasuredHeight();
                    float offset = (releasedChild.getTop() - slideViewHeight) * 1.0f / downViewHeight;
                    mHelper.settleCapturedViewAt(releasedChild.getLeft(), yvel > 0 || yvel == 0 && offset > 0.5f ? mUpView.getMeasuredHeight() : slideViewHeight);
                    invalidate();
                }
            }

            @Override
            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
                if(changedView == mUpView){
                    mDownView.setTop(top + mUpView.getMeasuredHeight());

                    mSlidePercent = (float) (-top) / mDownView.getMeasuredHeight();
                    if(mSlidePercent > 0.9f){
                        mSlideView.setTop(-mSlideView.getMeasuredHeight() + (int)((mSlidePercent - 0.9f)/(1-0.9) * mSlideView.getMeasuredHeight()));
                    }else{
                        mSlideView.setTop(-mSlideView.getMeasuredHeight());
                    }
                }else if(changedView == mDownView){
                    mUpView.setTop(top - mUpView.getMeasuredHeight());

                    mSlidePercent = (float) (mUpView.getMeasuredHeight() - top) / mDownView.getMeasuredHeight();
                    if(mSlidePercent > 0.9f){
                        mSlideView.setTop(-mSlideView.getMeasuredHeight() + (int)((mSlidePercent - 0.9f)/(1-0.9) * mSlideView.getMeasuredHeight()));
                    }else{
                        mSlideView.setTop(-mSlideView.getMeasuredHeight());
                    }
                }
                requestLayout();
            }

            @Override
            public int getViewVerticalDragRange(View child) {
                return child == mUpView ? mUpView.getMeasuredHeight() - mSlideView.getMeasuredHeight() :
                        child == mDownView ? mDownView.getMeasuredHeight() :
                        child == mSlideView ? mSlideView.getMeasuredHeight() : 0;
            }
        });
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(widthSize, heightSize);

        mUpView = getChildAt(0);
        mDownView = getChildAt(1);
        mSlideView = getChildAt(2);

        //up
        MarginLayoutParams lp = (MarginLayoutParams) mUpView.getLayoutParams();
        int widthSpec = MeasureSpec.makeMeasureSpec(
                widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
        int heightSpec = MeasureSpec.makeMeasureSpec(
                heightSize - lp.topMargin - lp.bottomMargin, MeasureSpec.EXACTLY);
        mUpView.measure(widthSpec, heightSpec);

        //slide
        lp = (MarginLayoutParams) mSlideView.getLayoutParams();
        widthSpec = getChildMeasureSpec(widthMeasureSpec,
                lp.leftMargin + lp.rightMargin, lp.width);
        heightSpec = getChildMeasureSpec(heightMeasureSpec,
                lp.topMargin + lp.bottomMargin, lp.height);
        mSlideView.measure(widthSpec, heightSpec);

        //down
        lp = (MarginLayoutParams) mDownView.getLayoutParams();
        widthSpec = MeasureSpec.makeMeasureSpec(
                widthSize - lp.leftMargin - lp.rightMargin, MeasureSpec.EXACTLY);
        heightSpec = MeasureSpec.makeMeasureSpec(
                heightSize - lp.topMargin - lp.bottomMargin - mSlideView.getMeasuredHeight(), MeasureSpec.EXACTLY);
        mDownView.measure(widthSpec, heightSpec);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        mInLayout = true;
        MarginLayoutParams lp = (MarginLayoutParams) mUpView.getLayoutParams();
        int upTop;
        if(mFirstLayout){
            upTop = lp.topMargin;
        }else{
            upTop = mUpView.getTop();
        }
        mUpView.layout(lp.leftMargin, upTop,
                lp.leftMargin + mUpView.getMeasuredWidth(),
                upTop + mUpView.getMeasuredHeight());

        lp = (MarginLayoutParams) mDownView.getLayoutParams();
        int downTop;
        if(mFirstLayout){
            downTop = mUpView.getMeasuredHeight() + lp.topMargin;
        }else{
            downTop = mDownView.getTop();
        }
        mDownView.layout(lp.leftMargin, downTop,
                lp.leftMargin + mDownView.getMeasuredWidth(),
                downTop + mDownView.getMeasuredHeight());

        lp = (MarginLayoutParams) mSlideView.getLayoutParams();
        int slideTop;
        if(mFirstLayout){
            slideTop = - mSlideView.getMeasuredHeight() + lp.topMargin;
        }else{
            slideTop = mSlideView.getTop();
        }
        mSlideView.layout(lp.leftMargin, slideTop,
                lp.leftMargin + mSlideView.getMeasuredWidth(),
                slideTop + mSlideView.getMeasuredHeight());


        mInLayout = false;
        mFirstLayout = false;
    }


    @Override
    public void requestLayout() {
        if(!mInLayout) {
            super.requestLayout();
        }
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        mFirstLayout = true;
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        mFirstLayout = true;
    }

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


    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mHelper.processTouchEvent(event);
        return true;
    }

    @Override
    public void computeScroll() {
        if (mHelper.continueSettling(true)) {
            invalidate();
        }
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new MarginLayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected LayoutParams generateLayoutParams(LayoutParams p) {
        return new MarginLayoutParams(p);
    }

    public float getSlidePercent(){
        return mSlidePercent;
    }

    public void slideToDown(){
        mHelper.smoothSlideViewTo(mDownView, mDownView.getLeft(), mSlideView.getMeasuredHeight());
        invalidate();
    }

    public void slideToUp(){
        mHelper.smoothSlideViewTo(mUpView, mUpView.getLeft(), 0);
        invalidate();
    }

}

3、Activity中可通过如下方法设置自动切换上下页面：

SlideUpLayout layout = (SlideUpLayout)findViewById(R.id.slide_layout);
        if(layout.getSlidePercent() == 0) {
            layout.slideToDown();
        }

三、掌握了ViewDragHelper的使用，应该做什么拖拽之类效果都很轻松了

四、这里面其实还有个事件分派拦截的问题，下一篇文章会继续讲。参考《重写ViewGroup并借助ViewDragHelper实现各种拖拽交互效果（二）》，地址 http://blog.csdn.net/lin_dianwei/article/details/79210877

重写ViewGroup并借助ViewDragHelper实现各种拖拽交互效果（一）

系統應用Gallery2編譯過程記錄

EditText禁止自動彈出軟鍵盤

View顯示和隱藏動畫效果

Java反射

播放器常用手勢操控封裝GestureView

Mac下配置sublime實現LaTeX

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結