前言

这里只是一个小demo
先上效果图吧

源码如下：

public class MiddleHorizontalScrollView extends HorizontalScrollView {
    int current = -1; //当前位于中间item的位置
    double halfScreenWidth; //屏幕宽度的一半
    LinearLayout linearLayout; //内容布局
    int itemCount;//item的个数

    public MiddleHorizontalScrollView(Context context) {
        super(context, null);

    }

    public MiddleHorizontalScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        halfScreenWidth =1.0* getScreenWidth(context)/2;
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        //初始化时候确认中间item放大
        if (getChildCount() > 0 && current == -1) {
            linearLayout = (LinearLayout) getChildAt(0);
            itemCount = linearLayout.getChildCount();
            for (int i = 0; i < itemCount - 1; i++) {
                if (linearLayout.getChildAt(i).getX() - l < halfScreenWidth && linearLayout.getChildAt(i + 1).getX() - l >= halfScreenWidth) {
                    TextView currentTxt = (TextView) linearLayout.getChildAt(i);
                    currentTxt.setTextSize(40);
                    currentTxt.setTextColor(Color.GREEN);
                    current = i;
                    break;
                }
            }
        }
    }


    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (current > 0 && linearLayout != null){
            TextView currentTxt = (TextView) linearLayout.getChildAt(current);
            //如果该item仍位于屏幕中间位置
            if (currentTxt.getX() - l < halfScreenWidth && linearLayout.getChildAt(current + 1).getX() - l >= halfScreenWidth) {
                currentTxt.setTextSize(40);
                currentTxt.setTextColor(Color.GREEN);
            }
            else {
                currentTxt.setTextSize(20);
                currentTxt.setTextColor(Color.RED);
                //寻找位于屏幕中间的item
                if (l > oldl) { //向右滑动
                    if (current < itemCount - 2)
                        for (int i = current + 1; i < itemCount - 1; i++) {
                            if (linearLayout.getChildAt(i).getX() - l < halfScreenWidth && linearLayout.getChildAt(i + 1).getX() - l >= halfScreenWidth) {
                                TextView txt = (TextView) linearLayout.getChildAt(i);
                                txt.setTextSize(40);
                                txt.setTextColor(Color.GREEN);
                                current = i;
                                break;
                            }
                        }
                }
                else {//向左滑动
                    if (current > 1)
                        for (int i = current - 1; i > 1; i--) {
                            if (linearLayout.getChildAt(i).getX() - l < halfScreenWidth && linearLayout.getChildAt(i + 1).getX() - l >= halfScreenWidth) {
                                TextView txt = (TextView) linearLayout.getChildAt(i);
                                txt.setTextSize(40);
                                txt.setTextColor(Color.GREEN);
                                current = i;
                                break;
                            }
                        }
                }
            }
        }
    }

    /**
     * 获取屏幕宽度
     */
    public static int getScreenWidth(Context context) {
        Display display = ((WindowManager) context
                .getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();
        return display.getWidth();
    }

}

   <com.demo.viewdemo.MiddleHorizontalScrollView

        android:id="@+id/horizontalScrollView"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:scrollbars="none" >

        <LinearLayout

            android:id="@+id/content"

            android:layout_width="fill_parent"

            android:layout_height="200dp"

            android:layout_centerVertical="true"

            android:orientation="horizontal"

            />

    </com.demo.viewdemo.MiddleHorizontalScrollView>

       contentLinear= (LinearLayout) findViewById(R.id.content);
        horizontalScrollView= (MiddleHorizontalScrollView) findViewById(R.id.horizontalScrollView);
        contentLinear.removeAllViews();
        for (int i = 0; i < 50; i++) {
            TextView child = new TextView(this);
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(80, ViewGroup.LayoutParams.MATCH_PARENT);
            params.gravity=Gravity.CENTER;
            child.setTextSize(20);
            child.setTextColor(Color.RED);
            child.setGravity(Gravity.CENTER);
            child.setText(""+i);
            contentLinear.addView(child,params);
        }