转载请声明出处http://blog.csdn.net/zhongkejingwang/article/details/38656929
用手机淘宝浏览商品详情时,商品图片是放在后面的,在第一个ScrollView滚动到最底下时会有提示,继续拖动才能浏览图片。仿照这个效果写一个出来并不难,只要定义一个Layout管理两个ScrollView就行了,当第一个ScrollView滑到底部时,再次向上滑动进入第二个ScrollView。效果如下:
需要注意的地方是:
1、如果是手动滑到底部需要再次按下才能继续往下滑,自动滚动到底部则不需要
2、在由上一个ScrollView滑动到下一个ScrollView的过程中多只手指相继拖动也不会导致布局的剧变,也就是多个pointer的滑动不会导致move距离的剧变。
这个Layout的实现思路是:
在布局中放置两个ScrollView,并为其设置OnTouchListener,时刻判断ScrollView的滚动距离,一旦第一个ScrollView滚动到底部,则标识改为可向上拖动,此时开始记录滑动距离mMoveLen,根据mMoveLen重新layout两个ScrollView;同理,监听第二个ScrollView是否滚动到顶部,以往下拖动。
OK,明白了原理之后可以看代码了:
package com.jingchen.tbviewer; import java.util.Timer; import java.util.TimerTask; import android.content.Context; import android.os.Handler; import android.os.Message; import android.util.AttributeSet; import android.view.MotionEvent; import android.view.VelocityTracker; import android.view.View; import android.widget.RelativeLayout; import android.widget.ScrollView; /** * 包含两个ScrollView的容器 * * @author chenjing * */ public class ScrollViewContainer extends RelativeLayout { /** * 自动上滑 */ public static final int AUTO_UP = 0; /** * 自动下滑 */ public static final int AUTO_DOWN = 1; /** * 动画完成 */ public static final int DONE = 2; /** * 动画速度 */ public static final float SPEED = 6.5f; private boolean isMeasured = false; /** * 用于计算手滑动的速度 */ private VelocityTracker vt; private int mViewHeight; private int mViewWidth; private View topView; private View bottomView; private boolean canPullDown; private boolean canPullUp; private int state = DONE; /** * 记录当前展示的是哪个view,0是topView,1是bottomView */ private int mCurrentViewIndex = 0; /** * 手滑动距离,这个是控制布局的主要变量 */ private float mMoveLen; private MyTimer mTimer; private float mLastY; /** * 用于控制是否变动布局的另一个条件,mEvents==0时布局可以拖拽了,mEvents==-1时可以舍弃将要到来的第一个move事件, * 这点是去除多点拖动剧变的关键 */ private int mEvents; private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { if (mMoveLen != 0) { if (state == AUTO_UP) { mMoveLen -= SPEED; if (mMoveLen <= -mViewHeight) { mMoveLen = -mViewHeight; state = DONE; mCurrentViewIndex = 1; } } else if (state == AUTO_DOWN) { mMoveLen += SPEED; if (mMoveLen >= 0) { mMoveLen = 0; state = DONE; mCurrentViewIndex = 0; } } else { mTimer.cancel(); } } requestLayout(); } }; public ScrollViewContainer(Context context) { super(context); init(); } public ScrollViewContainer(Context context, AttributeSet attrs) { super(context, attrs); init(); } public ScrollViewContainer(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(); } private void init() { mTimer = new MyTimer(handler); } @Override public boolean dispatchTouchEvent(MotionEvent ev) { switch (ev.getActionMasked()) { case MotionEvent.ACTION_DOWN: if (vt == null) vt = VelocityTracker.obtain(); else vt.clear(); mLastY = ev.getY(); vt.addMovement(ev); mEvents = 0; break; case MotionEvent.ACTION_POINTER_DOWN: case MotionEvent.ACTION_POINTER_UP: // 多一只手指按下或抬起时舍弃将要到来的第一个事件move,防止多点拖拽的bug mEvents = -1; break; case MotionEvent.ACTION_MOVE: vt.addMovement(ev); if (canPullUp && mCurrentViewIndex == 0 && mEvents == 0) { mMoveLen += (ev.getY() - mLastY); // 防止上下越界 if (mMoveLen > 0) { mMoveLen = 0; mCurrentViewIndex = 0; } else if (mMoveLen < -mViewHeight) { mMoveLen = -mViewHeight; mCurrentViewIndex = 1; } if (mMoveLen < -8) { // 防止事件冲突 ev.setAction(MotionEvent.ACTION_CANCEL); } } else if (canPullDown && mCurrentViewIndex == 1 && mEvents == 0) { mMoveLen += (ev.getY() - mLastY); // 防止上下越界 if (mMoveLen < -mViewHeight) { mMoveLen = -mViewHeight; mCurrentViewIndex = 1; } else if (mMoveLen > 0) { mMoveLen = 0; mCurrentViewIndex = 0; } if (mMoveLen > 8 - mViewHeight) { // 防止事件冲突 ev.setAction(MotionEvent.ACTION_CANCEL); } } else mEvents++; mLastY = ev.getY(); requestLayout(); break; case MotionEvent.ACTION_UP: mLastY = ev.getY(); vt.addMovement(ev); vt.computeCurrentVelocity(700); // 获取Y方向的速度 float mYV = vt.getYVelocity(); if (mMoveLen == 0 || mMoveLen == -mViewHeight) break; if (Math.abs(mYV) < 500) { // 速度小于一定值的时候当作静止释放,这时候两个View往哪移动取决于滑动的距离 if (mMoveLen <= -mViewHeight / 2) { state = AUTO_UP; } else if (mMoveLen > -mViewHeight / 2) { state = AUTO_DOWN; } } else { // 抬起手指时速度方向决定两个View往哪移动 if (mYV < 0) state = AUTO_UP; else state = AUTO_DOWN; } mTimer.schedule(2); try { vt.recycle(); } catch (Exception e) { e.printStackTrace(); } break; } super.dispatchTouchEvent(ev); return true; } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { topView.layout(0, (int) mMoveLen, mViewWidth, topView.getMeasuredHeight() + (int) mMoveLen); bottomView.layout(0, topView.getMeasuredHeight() + (int) mMoveLen, mViewWidth, topView.getMeasuredHeight() + (int) mMoveLen + bottomView.getMeasuredHeight()); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (!isMeasured) { isMeasured = true; mViewHeight = getMeasuredHeight(); mViewWidth = getMeasuredWidth(); topView = getChildAt(0); bottomView = getChildAt(1); bottomView.setOnTouchListener(bottomViewTouchListener); topView.setOnTouchListener(topViewTouchListener); } } private OnTouchListener topViewTouchListener = new OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { ScrollView sv = (ScrollView) v; if (sv.getScrollY() == (sv.getChildAt(0).getMeasuredHeight() - sv .getMeasuredHeight()) && mCurrentViewIndex == 0) canPullUp = true; else canPullUp = false; return false; } }; private OnTouchListener bottomViewTouchListener = new OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { ScrollView sv = (ScrollView) v; if (sv.getScrollY() == 0 && mCurrentViewIndex == 1) canPullDown = true; else canPullDown = false; return false; } }; class MyTimer { private Handler handler; private Timer timer; private MyTask mTask; public MyTimer(Handler handler) { this.handler = handler; timer = new Timer(); } public void schedule(long period) { if (mTask != null) { mTask.cancel(); mTask = null; } mTask = new MyTask(handler); timer.schedule(mTask, 0, period); } public void cancel() { if (mTask != null) { mTask.cancel(); mTask = null; } } class MyTask extends TimerTask { private Handler handler; public MyTask(Handler handler) { this.handler = handler; } @Override public void run() { handler.obtainMessage().sendToTarget(); } } } }
注释写的很清楚了,有几个关键点需要讲一下:
1、由于这里为两个ScrollView设置了OnTouchListener,所以在其他地方不能再设置了,否则就白搭了。
2、两个ScrollView的layout参数统一由mMoveLen决定。
3、变量mEvents有两个作用:一是防止手动滑到底部或顶部时继续滑动而改变布局,必须再次按下才能继续滑动;二是在新的pointer down或up时把mEvents设置成-1可以舍弃将要到来的第一个move事件,防止mMoveLen出现剧变。为什么会出现剧变呢?因为假设一开始只有一只手指在滑动,记录的坐标值是这个pointer的事件坐标点,这时候另一只手指按下了导致事件又多了一个pointer,这时候到来的move事件的坐标可能就变成了新的pointer的坐标,这时计算与上一次坐标的差值就会出现剧变,变化的距离就是两个pointer间的距离。所以要把这个move事件舍弃掉,让mLastY值记录这个pointer的坐标再开始计算mMoveLen。pointer up的时候也一样。
理解了这几点,看起来就没什么难度了,代码量也很小。
MainActivity的布局:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" > <com.jingchen.tbviewer.ScrollViewContainer android:layout_width="match_parent" android:layout_height="match_parent" > <ScrollView android:layout_width="match_parent" android:layout_height="match_parent" > <RelativeLayout android:layout_width="wrap_content" android:layout_height="wrap_content" > <LinearLayout android:id="@+id/imagesLayout" android:layout_width="match_parent" android:layout_height="wrap_content" android:gravity="center_horizontal" android:orientation="vertical" > <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/h" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/i" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/j" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/k" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/l" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/m" /> </LinearLayout> <TextView android:layout_width="match_parent" android:layout_height="60dp" android:layout_below="@id/imagesLayout" android:background="#eeeeee" android:gravity="center" android:text="继续拖动,查看更多美女" android:textSize="20sp" /> </RelativeLayout> </ScrollView> <ScrollView android:layout_width="match_parent" android:layout_height="match_parent" android:background="#000000" > <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center_horizontal" android:orientation="vertical" > <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/a" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/b" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/c" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/d" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/e" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/f" /> <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="@drawable/g" /> </LinearLayout> </ScrollView> </com.jingchen.tbviewer.ScrollViewContainer> </RelativeLayout>
在ScrollView中放了几张图片而已。
MainActivity的代码:
package com.jingchen.tbviewer; import android.app.Activity; import android.os.Bundle; import android.view.Menu; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); } @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.main, menu); return true; } }
啥也没有......
好了,到此结束~