一般进入APP都有欢迎界面，基本都是水平滚动的，今天和大家分享一个垂直滚动的例子。
先来看看效果把：
首先是布局文件：
<com.example.verticallinearlayout.VerticalLinearLayout xmlns:android="/apk/res/android" xmlns:tools="/tools" android:id="@+id/id_main_ly" android:layout_width="match_parent" android:layout_height="fill_parent" android:orientation="vertical" android:background="#fff" > <RelativeLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/w02" > <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="hello" /> </RelativeLayout> <RelativeLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/w03" > <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:background="#fff" android:text="hello" /> </RelativeLayout> <RelativeLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/w04" > <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="hello" /> </RelativeLayout> <RelativeLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/w05" > <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" android:text="hello" /> </RelativeLayout> </com.example.verticallinearlayout.VerticalLinearLayout>
自定义的Layout了
package com.example.verticallinearlayout;import android.content.Context;import android.util.AttributeSet;import android.util.DisplayMetrics;import android.util.Log;import android.view.MotionEvent;import android.view.VelocityTracker;import android.view.View;import android.view.ViewGroup;import android.view.WindowManager;import android.widget.Scroller;public class VerticalLinearLayout extends ViewGroup{/*** 屏幕的高度*/private int mScreenHeight;/*** 手指按下时的getScrollY*/private int mScrollStart;/*** 手指抬起时的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;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);}@Overrideprotected 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, heightMeasureSpec);}}@Overrideprotected 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}}}}@Overridepublic boolean onTouchEvent(MotionEvent event){// 如果当前正在滚动，调用父类的onTouchEventif (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;// 边界值检查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;Log.i("test", "已经到达顶端，下拉多少，就往上滚动多少scrollY="+scrollY);}// 已经到达底部，上拉多少，就往下滚动多少if (dy > 0 && scrollY + dy > getHeight() - mScreenHeight){dy = getHeight() - mScreenHeight - scrollY;Log.i("test", "已经到达顶端，下拉多少，就往上滚动多少scrollY=="+scrollY);}Log.i("test", "dy="+dy+",scrollY"+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())// 往下滑动{if (shouldScrollToPre()){mScroller.startScroll(0, getScrollY(), 0, -mScreenHeight - dScrollY);} else{mScroller.startScroll(0, getScrollY(), 0, -dScrollY);}}isScrolling = true;postInvalidate();recycleVelocity();break;}return true;}/*** 根据滚动距离判断是否能够滚动到下一页* * @return*/private boolean shouldScrollToNext(){return mScrollEnd - mScrollStart > mScreenHeight / 2 || Math.abs(getVelocity()) > 600;}/*** 根据用户滑动，判断用户的意图是否是滚动到下一页* * @return*/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(getVelocity()) > 600;}/*** 根据用户滑动，判断用户的意图是否是滚动到上一页* * @return*/private boolean wantScrollToPre(){return mScrollEnd < mScrollStart;}@Overridepublic void computeScroll(){puteScroll();if (puteScrollOffset()){scrollTo(0, mScroller.getCurrY());postInvalidate();} else{int position = getScrollY() / mScreenHeight;Log.e("xxx", position + "," + currentPage);if (position != currentPage){if (mOnPageChangeListener != null){currentPage = position;mOnPageChangeListener.onPageChange(currentPage);}}isScrolling = false;}}/*** 获取y方向的加速度* * @return*/private int getVelocity(){puteCurrentVelocity(1000);return (int) mVelocityTracker.getYVelocity();}/*** 释放资源*/private void recycleVelocity(){if (mVelocityTracker != null){mVelocityTracker.recycle();mVelocityTracker = null;}}/*** 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);}/*** 设置回调接口* * @param onPageChangeListener*/public void setOnPageChangeListener(OnPageChangeListener onPageChangeListener){mOnPageChangeListener = onPageChangeListener;}/*** 回调接口* * @author zhy* */public interface OnPageChangeListener{void onPageChange(int currentPage);}}
释还是相当详细的，我简单描述一下，Action_down时获得当前的scrollY,然后Action_move时，根据移动的距离不断scrollby就行了，当前处理了一下边界判断，在Action_up中再次获得scrollY，两个的scrollY进行对比，然后根据移动的距离与方向决定最后的动作
MainActivity
package com.example.verticallinearlayout;import android.app.Activity;import android.os.Bundle;import android.widget.Toast;import com.example.verticallinearlayout.VerticalLinearLayout.OnPageChangeListener;public class MainActivity extends Activity{private VerticalLinearLayout mMianLayout;@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mMianLayout = (VerticalLinearLayout) findViewById(R.id.id_main_ly);mMianLayout.setOnPageChangeListener(new OnPageChangeListener(){@Overridepublic void onPageChange(int currentPage){// mMianLayout.getChildAt(currentPage);Toast.makeText(MainActivity.this, "第"+(currentPage+1)+"页", Toast.LENGTH_SHORT).show();}});}}
为了提供可扩展性，还是定义了回调接口，完全可以把这个当成一个垂直的ViewPager使用。
总结下：
Scroller这个辅助类还是相当好用的，原理我简单说一下：每次滚动时，让Scroller进行滚动，然后调用postInvalidate方法，这个方法会引发调用onDraw方法，onDraw方法中会去调用computeScroll方法，然后我们在computScroll中判断，Scroller的滚动是否结束，没有的话，把当前的View滚动到现在Scroller的位置，然后继续调用postInvalidate，这样一个循环的过程。
画张图方便大家理解，ps:没找到什么好的画图工具，那rose随便画了，莫计较。
源码
源码点击此处下载
