Android Scroller简单用法

1.知识点

在了解Scorller类之前应先知道View的ScrollTo(int x, int y)/ScrollBy(int x, int y)之间的区别,了解什么是视图坐标，什么是布局坐标。之后我们来看一下Scroller的源码。

Scoller一般用在自定义View中

public class Scroller  {  
   
    private int mStartX;    //起始坐标点 ,  X轴方向  
    private int mStartY;    //起始坐标点 ,  Y轴方向  
    private int mCurrX;     //当前坐标点  X轴， 即调用startScroll函数后,经过一定时间所达到的值  
    private int mCurrY;     //当前坐标点  Y轴， 即调用startScroll函数后,经过一定时间所达到的值  
      
    private float mDeltaX;  //应该继续滑动的距离， X轴方向  
    private float mDeltaY;  //应该继续滑动的距离， Y轴方向  
    private boolean mFinished;  //是否已经完成本次滑动操作， 如果完成则为 true  
   
    //构造函数  
    public Scroller(Context context) {  
        this(context, null);  
    }  
    public final boolean isFinished() {  
        return mFinished;  
    }  
    //强制结束本次滑屏操作  
    public final void forceFinished(boolean finished) {  
        mFinished = finished;  
    }  
    public final int getCurrX() {  
        return mCurrX;  
    }  
     /* Call this when you want to know the new location.  If it returns true, 
     * the animation is not yet finished.  loc will be altered to provide the 
     * new location. */   
    //根据当前已经消逝的时间计算当前的坐标点，保存在mCurrX和mCurrY值中  
    public boolean computeScrollOffset() {  
        if (mFinished) {  //已经完成了本次动画控制，直接返回为false  
            return false;  
        }  
        int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);  
        if (timePassed < mDuration) {  
            switch (mMode) {  
            case SCROLL_MODE:  
                float x = (float)timePassed * mDurationReciprocal;  
                ...  
                mCurrX = mStartX + Math.round(x * mDeltaX);  
                mCurrY = mStartY + Math.round(x * mDeltaY);  
                break;  
            ...  
        }  
        else {  
            mCurrX = mFinalX;  
            mCurrY = mFinalY;  
            mFinished = true;  
        }  
        return true;  
    }  
    //开始一个动画控制，由(startX , startY)在duration时间内前进(dx,dy)个单位，即到达坐标为(startX+dx , startY+dy)出  
    public void startScroll(int startX, int startY, int dx, int dy, int duration) {  
        mFinished = false;  
        mDuration = duration;  
        mStartTime = AnimationUtils.currentAnimationTimeMillis();  
        mStartX = startX;       mStartY = startY;  
        mFinalX = startX + dx;  mFinalY = startY + dy;  
        mDeltaX = dx;            mDeltaY = dy;  
        ...  
    }  
}

一些方法介绍

mScroller.getCurrX() //获取mScroller当前水平滚动的位置  
mScroller.getCurrY() //获取mScroller当前竖直滚动的位置  
mScroller.getFinalX() //获取mScroller最终停止的水平位置  
mScroller.getFinalY() //获取mScroller最终停止的竖直位置  
mScroller.setFinalX(int newX) //设置mScroller最终停留的水平位置，没有动画效果，直接跳到目标位置  
mScroller.setFinalY(int newY) //设置mScroller最终停留的竖直位置，没有动画效果，直接跳到目标位置  
   
//滚动，startX, startY为开始滚动的位置，dx,dy为滚动的偏移量, duration为完成滚动的时间  
mScroller.startScroll(int startX, int startY, int dx, int dy) //使用默认完成时间250ms  
mScroller.startScroll(int startX, int startY, int dx, int dy, int duration)  
   
mScroller.computeScrollOffset() //返回值为boolean，true说明滚动尚未完成，false说明滚动已经完成。这是一个很重要的方法，通常放在View.computeScroll()中，用来判断是否滚动是否结束。

View的computeScroll()方法使用，此方法在绘制View的每一个子view时都被调用

2.举例

实现下拉刷新的效果
主要代码：

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public class CustomView extends RelativeLayout {
 
    private static final String TAG = "CustomView";
 
    private Scroller mScroller;
    private GestureDetector mGestureDetector;
    public boolean flag = true;
    public StateListener stateListener;
    public CustomView(Context context) {
        this(context, null);
    }
     
    public CustomView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setClickable(true);
        setLongClickable(true);
        mScroller = new Scroller(context);
        mGestureDetector = new GestureDetector(context, new CustomGestureListener());
    }
    public interface StateListener
    {
        public void changeText();
        public void recoverText();
    }
    public void setStateListener(StateListener statelistener)
    {
        this.stateListener = statelistener;
    }
    //调用此方法滚动到目标位置
    public void smoothScrollTo(int fx, int fy) {
        int dx = fx - mScroller.getFinalX();
        int dy = fy - mScroller.getFinalY();
        smoothScrollBy(dx, dy);
    }
 
    //调用此方法设置滚动的相对偏移
    public void smoothScrollBy(int dx, int dy) {
 
        //设置mScroller的滚动偏移量
        mScroller.startScroll(mScroller.getFinalX(), mScroller.getFinalY(), dx, dy);
        invalidate();//这里必须调用invalidate()才能保证computeScroll()会被调用，否则不一定会刷新界面，看不到滚动效果
    }
     
    //在绘制View时，会在draw()过程调用该方法。
    @Override
    public void computeScroll() {
     
        //先判断mScroller滚动是否完成
        if (mScroller.computeScrollOffset()) {
         
            //这里调用View的scrollTo()完成实际的滚动
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
             
            //必须调用该方法，否则不一定能看到滚动效果
            postInvalidate();
        }
        super.computeScroll();
    }
     
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
        case MotionEvent.ACTION_UP :
            Log.i(TAG, "get Sy" + getScrollY());
            System.out.println(getScrollX()+"x--"+getScrollY()+"y");
            smoothScrollTo(0, 0);
            System.out.println("up");
            break;
        default:
            int distance = getScrollY();
            System.out.println("distance"+distance);
            if(distance <= 0)
            {
                flag = true;
                if(distance > -200)
                {
                    stateListener.recoverText();
                }
                else if(distance < -200)
                {
                    stateListener.changeText();
                }
                return mGestureDetector.onTouchEvent(event);
            }else
            {
                flag = false;
                return false;
            }
        }
        return super.onTouchEvent(event);
    }
     
    class CustomGestureListener implements GestureDetector.OnGestureListener {
 
        @Override
        public boolean onDown(MotionEvent e) {
            // TODO Auto-generated method stub
            return true;
        }
 
        @Override
        public void onShowPress(MotionEvent e) {
            // TODO Auto-generated method stub
             
        }
 
        @Override
        public boolean onSingleTapUp(MotionEvent e) {
            // TODO Auto-generated method stub
            return false;
        }
 
        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {
            if(flag)
            {int dis = (int)((distanceY-0.5)/4);
            Log.i(TAG, dis + ".");
            smoothScrollBy(0, dis);}
            return false;
        }
 
        @Override
        public void onLongPress(MotionEvent e) {
            // TODO Auto-generated method stub
             
        }
 
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
                float velocityY) {
            // TODO Auto-generated method stub
            e1.getY();
            e2.getY();
            System.out.println(e1.getY()+"------"+e2.getY());
            return false;
        }
         
    }
}

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