竖直滑动View制作引导页

传承者（Inheritors）打造共同进步生态圈！！！

转载：http://write.blog.youkuaiyun.com/postedit/23692439

三段论：滑动所需要的准备，自定义ViewGoup，布局中使用

自定义ViewGoup

public class VerticalLinearLayout extends ViewGroup {


   public class VerticalLinearLayout extends ViewGroup {


    /**
     * 屏幕的高度
     */
    private int mScreenHeight;
    /**
     * 手指按下时的getScrollY
     */
    private int mScrollStart;
    /**
     * 手指抬起时getScrollY
     */
    private int mScrollEnd;
    /**
     * 记录移动时的Y
     */
    private int mLastY;
    /**
     * 滚动的辅助类
     */
    private Scroller mScroller;
    /**
     * 是否正在滚动
     */
    private boolean isScrolling;

    /**
     * 加速度检测
     *
     */
    private VelocityTracker mVelocityTracker;

    /**
     * 记录当前页
     *
     */
    private int currentPage = 0;

    private OnPageChangeListener mOnPageChangeListener;
    private int childHeight;


    public VerticalLinearLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        /**
         * 获得屏幕的高度
         */
        WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
        DisplayMetrics outMetrics = new DisplayMetrics();
        wm.getDefaultDisplay().getMetrics(outMetrics);
        mScreenHeight = outMetrics.heightPixels;

        //初始化
        mScroller = new Scroller(context);



    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View childView = getChildAt(i);

            measureChild(childView,widthMeasureSpec,mScreenHeight);
        }

    }



    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if(changed){
            int childCount = getChildCount();
            //设置主布局的高度
            MarginLayoutParams lp = (MarginLayoutParams) getLayoutParams();
            lp.height = mScreenHeight*childCount;
            setLayoutParams(lp);

            for (int i = 0; i < childCount; i++) {
                View child = getChildAt(i);
                if(child.getVisibility() != View.GONE){
                    child.layout(l,i*mScreenHeight,r,(i+1)*mScreenHeight);//调用每个自布局的layout
                }
                childHeight = getChildAt(0).getMeasuredHeight();
            }
        }

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {


        //如果当前正在滚动，调用父类的onTouchEvent
        if (isScrolling) {
            return super.onTouchEvent(event);
        }
         int action =event.getAction();
        int y = (int)event.getY();

        obtainVelocity(event);
        switch (action){
            case MotionEvent.ACTION_DOWN:
                mScrollStart = getScrollY();
                mLastY =  y;
                break;
            case MotionEvent.ACTION_MOVE:
                if(!mScroller.isFinished()){
                    mScroller.abortAnimation();
                }
                int dy = mLastY - y;
                //边际值检查
                int scrollY = getScrollY();

               //已经到达顶端，下拉多少，就往上滚动多少
                if(dy<0 && scrollY+dy < 0 ){
                  dy = -scrollY;
                }
                //已经达到底部了，上拉多少，留往下滚动多少
                if(dy>0 && scrollY+dy > getHeight() - mScreenHeight){
                   dy = getHeight() - mScreenHeight - scrollY;
                }
                scrollBy(0,dy);

                mLastY = y;
                break;
            case MotionEvent.ACTION_UP:
                mScrollEnd = getScrollY();
                int dScrollY = mScrollEnd - mScrollStart;
                if(wantScrollToNext()){
                    //往上滑动
                    if(shouldScrollToNext()){
                        mScroller.startScroll(0,getScrollY(),0, mScreenHeight - dScrollY);

                    }else{
                        mScroller.startScroll(0,getScrollY(),0,-dScrollY);
                    }
                }
                if(wantScrollToPre()){
                    //往下下滑
                    if(shouldScrollToPre()){
                        mScroller.startScroll(0,getScrollY(),0,-mScreenHeight - dScrollY);

                    }else{
                        mScroller.startScroll(0,getScrollY(),0 , -dScrollY);
                    }
                }
                isScrolling = true;
                postInvalidateDelayed(0);
                recycleVelocity();
                break;
        }
        return  true;
    }

    /**
     * 根据滚动距离判断是否能够滚动到下一页
     */
    private boolean shouldScrollToNext() {


        return mScrollEnd - mScrollStart > mScreenHeight / 2 || Math.abs(getYVelocity()) > 600;
    }

    /**
     * 根据用户滑动，判断用户的意图是否是滚动到下一页
     *
     */
    private boolean wantScrollToNext(){
        return mScrollEnd> mScrollStart ;
    }

    /**
     * 根据滚动距离判断是否能够滚动到上一页
     * @return
     */
    private boolean shouldScrollToPre(){

        return -mScrollEnd + mScrollStart > mScreenHeight / 2 || Math.abs(getYVelocity())>600;
    }

    /**
     * 根据用户滑动，判断用户意图是否是滚动到上一页
     * @return
     */
    private boolean wantScrollToPre(){

        return mScrollEnd < mScrollStart;
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        if(mScroller.computeScrollOffset()){
            scrollTo(0,mScroller.getCurrY());
            postInvalidate();
        }else {
            int position = getScrollY() / mScreenHeight;
            if(position != currentPage){
                if(mOnPageChangeListener!= null){
                currentPage = position;
                mOnPageChangeListener.onPageChange(currentPage);
            }}
            isScrolling = false;
        }


    }

    /**
     * 初始化加速度检测器
     * @param event
     */
    private void obtainVelocity(MotionEvent event) {
        if(mVelocityTracker == null){
            mVelocityTracker = VelocityTracker.obtain();

        }
        mVelocityTracker.addMovement(event);
    }


    /**
     * 资源释放
     */
    private void recycleVelocity(){
        if(mVelocityTracker != null){
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    /**
     * 设置回调接口
     * @param onPageChangeListener
     */
    public void setOnPageChangeListener(OnPageChangeListener onPageChangeListener){
        mOnPageChangeListener = onPageChangeListener;
    }

    public int getYVelocity() {

        mVelocityTracker.computeCurrentVelocity(1000);

        return (int) mVelocityTracker.getYVelocity();
    }

    public interface  OnPageChangeListener{
        void onPageChange(int  currentPage);
    }
}

布局出来

<com.example.administrator.testapplication.VerticalLinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:id="@+id/id_main_ly"
    android:background="#fff"
    tools:context="com.example.administrator.testapplication.MainActivity">


     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@mipmap/shenang"
         >

     </RelativeLayout>
     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@mipmap/dragon_boat"
         >

     </RelativeLayout>
     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@mipmap/zhagao"
         >

     </RelativeLayout>
     <RelativeLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:background="@mipmap/dragon_boat_fes"
         >
     </RelativeLayout>
</com.example.administrator.testapplication.VerticalLinearLayout>

在Activity中使用

public class MainActivity extends Activity {
private VerticalLinearLayout mMainLayout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mMainLayout = (VerticalLinearLayout) findViewById(R.id.id_main_ly);
        mMainLayout.setOnPageChangeListener(new VerticalLinearLayout.OnPageChangeListener() {
            @Override
            public void onPageChange(int currentPage) {
                Toast.makeText(MainActivity.this, "第"+(currentPage+1)+"页", Toast.LENGTH_SHORT).show();
            }
        });

    }

}