转载请表明出处:http://write.blog.csdn.net/postedit/23692439
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:
1、首先是布局文件:
<com.example.verticallinearlayout.VerticalLinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/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>
在自定义的ViewGroup中放入了4个RelativeLayout,每个RelativeLayout都设置了背景图片,背景图片来自微信~
2、主要看自定义的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); } @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 } } } } @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; } // 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; } 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; } @Override public void computeScroll() { super.computeScroll(); if (mScroller.computeScrollOffset()) { 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() { mVelocityTracker.computeCurrentVelocity(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); }}
注释还是相当详细的,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。
3、主Activity
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; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mMianLayout = (VerticalLinearLayout) findViewById(R.id.id_main_ly); mMianLayout.setOnPageChangeListener(new OnPageChangeListener() { @Override public 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。
源码点击此处下载
再分享一下我老师大神的人工智能教程吧。零基础!通俗易懂!风趣幽默!还带黄段子!希望你也加入到我们人工智能的队伍中来!https://blog.csdn.net/jiangjunshow