Scroller 学习

Scroller是Android中一个辅助View滑动的一个工具。它可以使View滑动有一个平滑的效果。下面是Scroller的一个简单实现。</span>

主要是要调用Scroller的一些方法

startScroll(int startX, int startY, int dx, int dy, int duration)

然后在所在View中重写computeScroll()

</pre><pre name="code" class="java"> @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }

下面是一个简单的应用。

package com.yyw.scrollerdemo;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ViewGroup;
import android.view.animation.DecelerateInterpolator;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.Scroller;

/**
 * Created by yyw on 2016/4/28.
 */
public class SliderLayout extends LinearLayout {
    public static final String TAG = "SliderLayout";
    private Scroller mScroller;
    private int totalNum = 8;
    private int index = 0;
    private ImageView mSlider;
    private GestureDetector detector;
    private Drawable mSliderImage;

    public SliderLayout(Context context) {
        this(context, null);
    }

    public SliderLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public SliderLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.SliderLayout);
        mSliderImage = array.getDrawable(R.styleable.SliderLayout_slider_pic);
        if (mSliderImage == null) {
            mSliderImage = context.getResources().getDrawable(R.drawable.slider);
        }
        array.recycle();
        init(context);
    }

    public int getIndex() {
        return index;

    }

    public void setIndex(int index) {
        if (this.index != index && index < totalNum && index >= 0) {
            if (getOrientation() == HORIZONTAL){
                horizontalScroll(index);
            }else {
                verticalScroll(index);
            }
            this.index = index;
        }

    }
    //水平滑动
    private void horizontalScroll(int index) {
        int dx = (this.index - index) * (getWidth() / totalNum);//计算偏移量
        if (mScroller.computeScrollOffset()) {
            mScroller.abortAnimation();
        }
        mScroller.startScroll(mScroller.getFinalX(), 0, dx, 0);//开始移动
        invalidate();
    }
    //垂直滑动
    private void verticalScroll(int index) {
        int dy = (this.index - index) * (getHeight() / totalNum);//计算偏移量
        if (mScroller.computeScrollOffset()) {
            mScroller.abortAnimation();
        }
        mScroller.startScroll(0, mScroller.getFinalY(), 0, dy);//开始移动
        invalidate();
    }
    public int getTotalNum() {
        return totalNum;
    }

    public void setTotalNum(int totalNum) {
        if (this.totalNum != totalNum && totalNum > 0) {
            this.totalNum = totalNum;
            if (index >= totalNum) {
                index = totalNum - 1;
            }
            resetSlider();
        }

    }

    private void init(Context context) {
        detector = new GestureDetector(context, mOnGestureListener);
        mScroller = new Scroller(context, new DecelerateInterpolator());
        mSlider = new ImageView(context);
        mSlider.setImageDrawable(mSliderImage);
        addView(mSlider, ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if (changed) {
            resetSlider();
        }
    }

    /**
     * 重新设置滑块
     */
    private void resetSlider() {
        if (getOrientation() == HORIZONTAL) {
            resetHorizontalSlider();
        }else {
            resetVerticalSlider();
        }
    }

    private void resetVerticalSlider() {
        int scrollY = getScrollY();
        int height = getHeight();
        LayoutParams params = (LayoutParams) mSlider.getLayoutParams();
        params.height = height / totalNum;//重新设置滑块的大小
        params.width = ViewGroup.LayoutParams.MATCH_PARENT;
        mSlider.setLayoutParams(params);
        int dy = -height / totalNum * index - scrollY;//计算滑块需要移动的位置，上 + ，下 - ；
        if (mScroller.computeScrollOffset()) {
            mScroller.abortAnimation();//如果Scroller没有结束就结束动画
        }
        mScroller.startScroll(0, mScroller.getFinalY(), 0, dy);//开始滑动
        invalidate();//必须要加上，不然没有滑动
    }
    private void resetHorizontalSlider() {
        int scrollX = getScrollX();
        int width = getWidth();
        LayoutParams params = (LayoutParams) mSlider.getLayoutParams();
        params.width = width / totalNum;//重新设置滑块的大小
        params.height = ViewGroup.LayoutParams.MATCH_PARENT;
        mSlider.setLayoutParams(params);
        int dx = -width / totalNum * index - scrollX;//计算滑块需要移动的位置，左 + ，右 - ；
        if (mScroller.computeScrollOffset()) {
            mScroller.abortAnimation();//如果Scroller没有结束就结束动画
        }
        mScroller.startScroll(mScroller.getFinalX(), 0, dx, 0);//开始滑动
        invalidate();//必须要加上，不然没有滑动
    }

    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            postInvalidate();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        detector.onTouchEvent(event);
        return true;
    }

    private GestureDetector.SimpleOnGestureListener mOnGestureListener = new GestureDetector.SimpleOnGestureListener() {
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            float dx = e1.getX() - e2.getX();
            if (Math.abs(velocityX) < 1000 && Math.abs(velocityY) < 500 && Math.abs(dx) < 100) {
                onSingleTapConfirmed(e2);
            }
            return true;
        }

        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {

            if (getOrientation() == HORIZONTAL) {
                float x = e.getX();
                float childW = getWidth() / totalNum;
                int column = (int) (x / childW);
                Log.i(TAG, "onSingleTapConfirmed: column " + column);
                setIndex(column);
            }else{
                float y = e.getY();
                float childH = getHeight() / totalNum;
                int row = (int) (y / childH);
                Log.i(TAG, "onSingleTapConfirmed: row " + row);
                setIndex(row);
            }
            return true;
        }
    };
}

应用

<com.yyw.scrollerdemo.SliderLayout
       android:id="@+id/slider"
       android:background="@drawable/slider_bg"
       android:orientation="horizontal"
       android:layout_width="match_parent"
       app:slider_pic="@drawable/slider"
       android:layout_height="50dp"/>